NKGen Biotech, Inc. Common Stock (NKGN) 10-Q 20 May 24 2024 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2024	May 20, 2024
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	001-40427
Entity Registrant Name	NKGen Biotech, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	86-2191918
Entity Address, Address Line One	3001 Daimler Street
Entity Address, City or Town	Santa Ana
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92705
City Area Code	(949)
Local Phone Number	396-6830
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		24,887,799
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001845459
Amendment Flag	false
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	NKGN
Security Exchange Name	NASDAQ
Warrant
Document Information [Line Items]
Title of 12(b) Security	Warrants, each whole warrant exercisable for one share of Common Stock at an exercise price of $11.50 per share
Trading Symbol	NKGNW
Security Exchange Name	NASDAQ

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 34	$ 26
Restricted cash	250	250
Prepaid expenses and other current assets	1,323	1,654
Total current assets	1,607	1,930
Property and equipment, net	14,136	14,459
Operating lease right-of-use asset, net	482	0
Capitalized software, net	91	92
Total assets	16,316	16,481
Current liabilities:
Accounts payable and accrued expenses (including related party amounts of $688 as of each of March 31, 2024 and December 31, 2023)	15,313	13,395
Bridge loans	215	0
Revolving line of credit	4,991	4,991
Related party loans	5,000	5,000
Operating lease liability, current	154	0
Other current liabilities (including related party amounts of zero and $202 as of March 31, 2024 and December 31, 2023, respectively)	366	262
Forward purchase derivative liabilities	10,085	15,804
Total current liabilities	37,483	39,452
Deferred tax liabilities	33	33
Operating lease liability, non-current	348	0
Derivative warrant liabilities	23,360	25,759
Senior convertible promissory notes, noncurrent, due to related parties	10,147	9,930
Total liabilities	71,371	75,174
Commitments and contingencies (Note 14)
Stockholders’ deficit:
Total liabilities	2	2
Additional paid-in capital	122,844	121,727
Subscription receivable	(10,389)	(17,792)
Receivable from shareholder	0	(500)
Accumulated deficit	(167,512)	(162,130)
Total stockholders’ deficit	(55,055)	(58,693)
Total liabilities and stockholders’ deficit	16,316	16,481
Convertible 12% promissory notes
Current liabilities:
Convertible notes	728	0
Bridge Loan
Current liabilities:
Convertible notes	$ 631	$ 0

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Costs and expenses:
Research and development expenses	$ 3,236	$ 3,599
General and administrative expenses	4,385	3,199
Total expenses	7,621	6,798
Loss from operations	(7,621)	(6,798)
Other income (expense):
Interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)	(1,069)	(34)
Loss on amendment of forward purchase contracts	(396)	0
Loss on issuance of convertible notes	729	0
Gain on amendment of PIPE warrant agreement	679	0
Other income (loss), net	(19)	11
Net loss before provision for income taxes	(5,382)	(8,322)
Net loss	(5,382)	(8,322)
Comprehensive loss	$ (5,382)	$ (8,322)
Earnings Per Share [Abstract]
Weighted-average common shares outstanding, basic (in shares)	21,935,679	13,313,132
Weighted-average common shares outstanding, diluted (in shares)	21,935,679	13,313,132
Net loss per share, basic (in usd per share)	$ (0.25)	$ (0.63)
Net loss per share, diluted (in usd per share)	$ (0.25)	$ (0.63)
Forward Purchase Derivative Liabilities
Other income (expense):
Change in fair value of forward purchase derivative liabilities	$ 535	$ 0
Warrant
Other income (expense):
Change in fair value of forward purchase derivative liabilities	3,716	0
Convertible 12% promissory notes
Other income (expense):
Change in fair value of convertible debt	(478)	0
Legacy Convertible Notes
Other income (expense):
Change in fair value of convertible debt	$ 0	$ (1,501)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)	$ 1,069	$ 34
Loss on issuance of convertible bridge loans (including related party amounts of $74 and zero for the three months ended March 31, 2024 and 2023, respectively)	$ (729)	0
Interest rate	12%
Related Party
Interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)	$ 698	33
Loss on issuance of convertible bridge loans (including related party amounts of $74 and zero for the three months ended March 31, 2024 and 2023, respectively)	$ (74)	$ 0

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ DEFICIT - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Subscription Receivable	Receivable from Shareholder	Accumulated Deficit	Previously Reported	Previously Reported Common Stock	Previously Reported Additional Paid-In Capital	Previously Reported Subscription Receivable	Previously Reported Receivable from Shareholder	Previously Reported Accumulated Deficit	Revision of Prior Period, Adjustment	Revision of Prior Period, Adjustment Common Stock	Revision of Prior Period, Adjustment Additional Paid-In Capital	Revision of Prior Period, Adjustment Subscription Receivable	Revision of Prior Period, Adjustment Receivable from Shareholder	Revision of Prior Period, Adjustment Accumulated Deficit
Balance as of beginning of period (in shares) at Dec. 31, 2022	0						32,575,043						(32,575,043)
Balance as of beginning of period at Dec. 31, 2022	$ 0						$ 33						$ (33)
Balance as of end of period (in shares) at Mar. 31, 2023	0
Balance as of end of period at Mar. 31, 2023	$ 0
Balance as of beginning of period (in shares) at Dec. 31, 2022		13,303,795						0						13,303,795
Beginning balance at Dec. 31, 2022	1,563	$ 1	$ 80,738	$ 0	$ 0	$ (79,176)	$ 1,563	$ 0	$ 80,706	$ 0	$ 0	$ (79,176)	$ 0	$ 1	$ 32	$ 0	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,258		1,258
Net loss	(8,322)					(8,322)
Exercise of common stock options (in shares)		11,354
Exercise of common stock options	4		4
Balance as of ending of period (in shares) at Mar. 31, 2023		13,315,149
Ending balance at Mar. 31, 2023	$ (5,497)	$ 1	82,000	0	0	(87,498)
Balance as of beginning of period (in shares) at Dec. 31, 2023	0
Balance as of beginning of period at Dec. 31, 2023	$ 0
Balance as of end of period (in shares) at Mar. 31, 2024	0
Balance as of end of period at Mar. 31, 2024	$ 0
Balance as of beginning of period (in shares) at Dec. 31, 2023		21,888,976
Beginning balance at Dec. 31, 2023	(58,693)	$ 2	121,727	(17,792)	(500)	(162,130)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	$ 1,117		1,117
Issuance of common stock in connection with the convertible debt (in shares)	500,000
Issuance of common stock in connection with the convertible debt	$ 0
Amendment of forward purchase contracts	2,764			2,764
Settlement of forward purchase contracts	4,639			4,639
Settlement of receivable from shareholder	500				500
Net loss	$ (5,382)					(5,382)
Exercise of common stock options (in shares)	0
Balance as of ending of period (in shares) at Mar. 31, 2024		22,388,976
Ending balance at Mar. 31, 2024	$ (55,055)	$ 2	$ 122,844	$ (10,389)	$ 0	$ (167,512)

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS	3 Months Ended		4 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Apr. 30, 2023 USD ($)
Operating Activities
Net loss	$ (5,382,000)	$ (8,322,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	295,000	304,000
Stock-based compensation	1,117,000	1,258,000
Amortization of right-of-use asset	31,000	0
Noncash lease expense	0	96,000
Noncash interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)	949,000	33,000
Loss on amendment of forward purchase contracts	396,000	0
Loss on issuance of convertible notes	729,000	0
Gain on amendment of PIPE warrant agreement	679,000	0
Loss on sale of property and equipment, net	8,000	0
Changes in operating assets and liabilities:
Accounts receivable	0	29,000
Prepaid expenses and other current assets	330,000	(137,000)
Accounts payable and accrued expenses	1,853,000	436,000
Other current liabilities	104,000	0
Operating lease liabilities	(11,000)	(99,000)
Other, net	(1,000)	(13,000)
Net cash used in operating activities	(4,034,000)	(4,914,000)
Investing activities
Sales of property and equipment	35,000	0
Purchases of capitalized software	0	(13,000)
Net cash provided by (used in) investing activities	35,000	(13,000)
Financing activities
Proceeds from exercise of common stock options	0	4,000
Proceeds from related party loans	0	4,500,000	$ 5,000,000
Proceeds from amendments to and settlements of select FPA agreements	1,823,000	0
Proceeds from issuance of bridge loans	200,000	0
Proceeds from amendment to the PIPE warrants	250,000	0
Repayments on paycheck protection loan	0	(46,000)
Payment of transaction costs	40,000	0
Proceeds from collection of the receivable from shareholder in connection with FPA agreement	500,000	0
Net cash provided by financing activities	4,007,000	5,558,000
Net increase in cash, cash equivalents, and restricted cash	8,000	631,000
Cash, cash equivalents, and restricted cash at the beginning of period	276,000	117,000	$ 117,000
Cash, cash equivalents, and restricted cash at the end of period	284,000	748,000
Cash and cash equivalents	34,000	748,000
Restricted cash	250,000	0
Total cash, cash equivalents, and restricted cash	284,000	748,000
Supplemental cash flow information
Cash paid for interest expense	120,000	0
Supplemental disclosure of noncash investing and financing activities
Deferred transaction costs included in accounts payable and accrued expenses	0	250,000
Capital Expenditures Incurred but Not yet Paid	15,000	0
Right-of-use asset obtained in exchange for new operating lease liability	$ 513,000	0
Interest rate	12%
Forward Purchase Derivative Liabilities
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of derivative liabilities	$ (535,000)	0
Warrant
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of derivative liabilities	(3,716,000)	0
Convertible bridge loans
Adjustments to reconcile net loss to net cash used in operating activities:
Loss on issuance of convertible notes	700,000
Financing activities
Proceeds from convertible debt	700,000	0
Convertible 12% promissory notes
Adjustments to reconcile net loss to net cash used in operating activities:
Change in the fair value of convertible debt	478,000	0
Financing activities
Proceeds from convertible debt	$ 574,000	0
Supplemental disclosure of noncash investing and financing activities
Interest rate	12%
Legacy Convertible Notes
Adjustments to reconcile net loss to net cash used in operating activities:
Change in the fair value of convertible debt	$ 0	1,501,000
Convertible Promissory Notes and Convertible Promissory Notes Due to Related Parties
Financing activities
Proceeds from convertible debt	$ 0	$ 1,100,000

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Accounts payable and accrued expenses (including related party amounts of $688 as of each of March 31, 2024 and December 31, 2023)	$ 15,313,000	$ 13,395,000
Interest rate	12%
Other current liabilities (including related party amounts of zero and $202 as of March 31, 2024 and December 31, 2023, respectively)	$ 366,000	$ 262,000
Common stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (shares)	500,000,000	500,000,000
Common stock, shares issued (in shares)	22,388,976	21,888,976
Common stock outstanding (in shares)	22,388,976	21,888,976
Convertible 12% promissory notes
Interest rate	12%
Convertible notes	$ 728,000	$ 0
Convertible 12% promissory notes | Convertible Debt
Interest rate	12%
Related Party
Accounts payable and accrued expenses (including related party amounts of $688 as of each of March 31, 2024 and December 31, 2023)	$ 688,000	688,000
Convertible notes	424,000	0
Other current liabilities (including related party amounts of zero and $202 as of March 31, 2024 and December 31, 2023, respectively)	$ 0	$ 202,000

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ DEFICIT (Parenthetical)	Mar. 31, 2024
Interest rate	12%
Convertible 12% promissory notes
Interest rate	12%
Convertible 12% promissory notes | Convertible Debt
Interest rate	12%

CONDENSED CONSOLIDATED STATEM_6

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Paid-in-kind interest	$ 949	$ 33
Loss on issuance of convertible notes	$ 729	0
Interest rate	12%
Convertible 12% promissory notes
Interest rate	12%
Related Party
Paid-in-kind interest	$ 698	33
Loss on issuance of convertible notes	$ 74	$ 0

Company Information

Company Information	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Company Information	Company Information NKGen Biotech, Inc. (“ Company ” or “ NKGen ”), a Delaware corporation headquartered in Santa Ana, California, is a clinical-stage biotechnology company focused on the development and commercialization of innovative autologous, allogeneic and CAR-NK natural killer cell therapies utilizing their proprietary SNK (Super-Natural-Killer) platform. The Company was formerly majority owned and controlled by NKMAX Co., Ltd. (“ NKMAX ”), a company formed under the laws of the Republic of Korea. The Company was originally incorporated in Delaware on January 28, 2021 under the name Graf Acquisition Corp. IV (“ Graf ”), as a special-purpose acquisition company for the purpose of effecting a merger, capital stock exchange, asset acquisition, stock purchase, reorganization or engaging in any other similar business combination with one or more businesses or entities. On April 14, 2023, the Company entered into the Agreement and Plan of Merger by and among Graf, Austria Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Graf (“ Merger Sub ”), and NKGen Biotech, Inc. (“ Merger Agreement ”). Upon consummation of the transactions under the Merger Agreement on September 29, 2023 (the “ Business Combination ”), Merger Sub merged with and into NKGen Biotech, Inc. (“ Legacy NKGen ”) with Legacy NKGen surviving the merger as a wholly owned subsidiary of Graf (the “ Merger ”). In connection with the consummation of the Business Combination (the “ Closing ”), Graf was renamed to “ NKGen Biotech, Inc. ” and Legacy NKGen changed its name to “ NKGen Operating Biotech, Inc. ” The common stock and warrants of the combined company began trading on The Nasdaq Stock Market LLC under the symbols “ NKGN ” and “ NKGNW ”, respectively, on October 2, 2023. Throughout the notes to the unaudited condensed consolidated financial statements, unless otherwise noted or otherwise suggested by context, the “ Company ” refers to Legacy NKGen prior to the consummation of the Business Combination, and the Company after the consummation of the Business Combination. Liquidity The Company follows Financial Accounting Standards Board (“ FASB ”) Accounting Standards Codification (“ ASC ”) Topic 205-40, Presentation of Financial Statements — Going Concern , which requires that management evaluate whether there are relevant conditions and events that in aggregate raise substantial doubt about the entity’s ability to continue as a going concern and to meet its obligations as they become due within one year after the date that the unaudited condensed consolidated financial statements are issued. Under the guidance, the Company must first evaluate whether there are conditions and events that raise substantial doubt about the entity’s ability to continue as a going concern (step 1). If the Company concludes substantial doubt is raised, management also is required to consider whether its plans alleviate that doubt (step 2). The Company has a limited operating history, has incurred significant operating losses since its inception, and the revenue and income potential of the Company’s business and market are unproven. The Company’s unaudited condensed consolidated financial statements are prepared using the generally accepted accounting principles applicable to a going concern, which contemplates the realization of assets and liquidation of liabilities in the normal course of business. As of March 31, 2024 , the Company had an accumulated deficit of $167.5 million and cash and cash equivalents of less than $0.1 million . To date, the Company has funded its operations primarily with the net proceeds from the issuance of senior convertible promissory notes, the issuance of related party loans, the issuance of bridge loans, the issuance of convertible bridge loans, the issuance of convertible 12% promissory notes, draws upon a revolving line of credit, the issuance and sale of equity securities, PIPE warrants, private placements, the amendment of private placements, and proceeds from the Business Combination. The Company expects to incur substantial operating losses for the next several years and will need to obtain additional near-term financing in order to continue its research and development activities, initiate and complete clinical trials and launch and commercialize any product candidates for which it receives regulatory approval. Management has prepared cash flow forecasts which indicate that based on the Company’s expected operating losses and negative cash flows, there is substantial doubt about the Company’s ability to continue as a going concern for twelve months from the issuance of these unaudited condensed consolidated financial statements. The Company plans to continue to fund its losses from operations and capital funding needs through additional debt or equity financings to be received from related parties, private equity, or other sources. If the Company is not able to secure adequate additional funding, the Company may be forced to make reductions in spending, extend payment terms with suppliers, liquidate assets where possible, suspend or curtail planned programs, or may be forced to cease operations or file for bankruptcy protection. Any of these actions could materially harm the Company’s business, results of operations and future prospects. There can be no assurance that such financing will be available or will be at terms acceptable to the Company. The preparation of these unaudited condensed consolidated financial statements does not include any adjustments that may result from the outcome of this uncertainty.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation NKMAX held a majority of the voting power of Legacy NKGen before the Business Combination and continued to hold a majority of the voting power of the Company after the Business Combination. Therefore, as there was no change in control, the Business Combination was accounted for as a common control transaction with respect to Legacy NKGen along with a reverse recapitalization of the Company. Accordingly, for accounting purposes, the financial statements of the Company represent a continuation of the financial statements of Legacy NKGen with the Business Combination being treated as the equivalent of Legacy NKGen issuing shares for the net assets of Graf, accompanied by a recapitalization. The net assets of Graf were recognized as of the Closing at historical cost, with no goodwill or other intangible assets recorded. Operations prior to the Business Combination are presented as those of Legacy NKGen and the accumulated deficit of Legacy NKGen has been carried forward after Closing. Upon the consummation of the Business Combination, all of Legacy NKGen’s equity was converted into equity of the Company based upon an exchange ratio (“ Exchange Ratio ”). In addition, all stock options of Legacy NKGen were converted using the Exchange Ratio into options exercisable for shares of the Company with the same terms and vesting conditions. The Exchange Ratio as of September 29, 2023, the date of Closing, was approximately 0.408. All periods prior to the Business Combination have been retrospectively adjusted using the Exchange Ratio to reflect the reverse recapitalization. In connection with the reverse recapitalization treatment of the Business Combination, all issued and outstanding securities of Graf upon Closing were treated as issuances of the Company upon the consummation of the Business Combination. The accompanying financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (“ SEC ”) and generally accepted accounting principles in the United States of America (“ US GAAP ”). The Company maintains its accounting records under the accrual method of accounting in conformity with US GAAP. The condensed consolidated balance sheet as of December 31, 2023 included herein was derived from the audited financial statements as of that date. Certain information and disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such regulations. Accordingly, these unaudited condensed consolidated financial statements and accompanying footnotes should be read in conjunction with NKGen’s financial statements as of and for the year ended December 31, 2023 . The results for the interim periods are not necessarily indicative of results for the full year. In the opinion of management, all adjustments, of a normal recurring nature, considered necessary for a fair presentation have been included in the unaudited condensed consolidated financial statements. The Company believes that the disclosures provided herein are adequate to prevent the information presented from being misleading. Principles of Consolidation The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All significant intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of unaudited condensed consolidated financial statements in accordance with US GAAP requires management to make estimates and assumptions that impact the reported amounts of certain assets and liabilities, certain disclosures at the date of the unaudited condensed consolidated financial statements, as well as the reported amounts of revenues and expenses during the reporting period. The most significant estimates in the Company’s unaudited condensed consolidated financial statements include, but are not limited to, accrued clinical and research and development expenses, legacy convertible notes, convertible 12% promissory notes, senior convertible promissory notes due to related parties, forward purchase derivative liabilities, derivative warrant liabilities, derivative warrant assets, common stock, and equity awards. These estimates and assumptions are based upon historical experience, knowledge of current events, and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results could differ materially from those estimates. Restricted Cash Restricted cash consists of funds that are contractually restricted due to a revolving line of credit, which was entered into during June 2023 . In accordance with the terms of the revolving line of credit, the Company was required to maintain $15.0 million in cash balances with the lender from March 31, 2024 until repayment of all principals and other payables to the lender under the revolving line of credit was made as additional collateral for the borrowings. In April 2024, the lender subsequently waived the minimum cash deposit requirement in exchange for the Company's agreement to use the lender as their primary banking relationship. As of both March 31, 2024 and December 31, 2023 , $0.3 million in restricted cash was recorded on the unaudited condensed consolidated balance sheet. The Company includes its restricted bank deposits in cash, cash equivalents and restricted cash when reconciling beginning-of-period and end-of-period total amounts shown on the unaudited condensed consolidated statements of cash flows for the three months ended March 31, 2024 . Deferred Debt Issuance Costs Costs incurred through the issuance of the revolving line of credit to parties who are providing short-term financing availability are reflected as deferred debt issuance costs. These costs are generally amortized to interest expense over the life of the financing instrument using the effective interest rate method or other methods approximating the effective interest method. As of both March 31, 2024 and December 31, 2023 , less than $0.1 million in deferred debt issuance costs were recorded to prepaid expenses and other current assets on the unaudited condensed consolidated balance sheets. Hybrid Instruments The Company follows Financial Accounting Standards Board (“ FASB ”) Accounting Standard Codification (“ ASC ”) 480, Distinguishing Liabilities from Equity , when evaluating the accounting for its hybrid instruments. A financial instrument that embodies an unconditional obligation, or a financial instrument other than an outstanding share that embodies a conditional obligation, that the issuer must or may settle by issuing a variable number of its equity shares shall be classified as a liability (or an asset in some circumstances) if, at inception, the monetary value of the obligation is based solely or predominantly on any one of the following: (a) a fixed monetary amount known at inception; (b) variations in something other than the fair value of the issuer’s equity shares; or (c) variations inversely related to changes in the fair value of the issuer’s equity shares. Hybrid instruments meeting these criteria are not further evaluated for any embedded derivatives and are carried as a liability at fair value at each balance sheet date. Derivative Instruments FASB ASC 815, Derivatives and Hedging Activities , requires companies to bifurcate certain features from their host instruments and account for them as free-standing derivative financial instruments should certain criteria be met. The Company does not use derivative instruments to hedge exposures to interest rate, market, or foreign currency risks. The Company evaluates its financial instruments to determine whether such instruments are derivatives or contain features that qualify as embedded derivatives. Embedded derivatives must be separately measured from the host contract if all the requirements for bifurcation are met. The assessment of the conditions surrounding the bifurcation of embedded derivatives depends on the nature of the host contract and the features of the derivatives. Bifurcated embedded derivatives are recognized at fair value, with changes in fair value recognized in the unaudited condensed consolidated statements of operations and comprehensive loss each period. Bifurcated embedded derivatives are classified with the related host contract in the Company’s unaudited condensed consolidated balance sheets. The classification of derivative instruments, including whether such instruments should be recorded as liabilities or as equity, is re-assessed at the end of each reporting period. Debt For convertible debt instruments that are not considered liabilities under ASC 480 or ASC 815, the Company applies ASC 470, Debt , for the accounting of such instruments, including any premiums or discounts. The Company’s bridge loans, senior convertible promissory notes, and convertible bridge loans accounted for under ASC 470. Accrued interest paid-in-kind is added to the carrying amount of the Company’s senior convertible promissory notes. Subscription and Shareholder Receivables The Company records stock issuances at the effective date. If the amounts are not funded upon issuance, the Company records a subscription receivable or shareholder receivable as an asset on the balance sheet. When subscription receivables or shareholder receivables are not received prior to the balance sheet date in satisfaction of the requirements under ASC 505, Equity , the subscription or shareholder receivable is reclassified as a contra account to stockholder’s equity (deficit) on the balance sheet. Shareholder receivables represent amounts due from shareholders. If the shareholder does not fund the receivable prior to the balance sheet date, the Company records a receivable that is reclassified as a contra account to stockholder’s deficit on the balance sheet. During March 31, 2024, $0.5 million due from shareholders was received by the Company. Impairment of Long-Lived Assets The Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate the carrying amount of an asset, or asset group, may not be recoverable. Recoverability is measured by a comparison of the carrying amount of an asset or asset group to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset or asset group exceeds its estimated future cash flows, an impairment charge is recognized by the amount by which the carrying amount of the asset or asset group exceeds the fair value of the asset or asset group. The Company has not recognized any impairment losses for the three months ended March 31, 2024 and 2023 . Fair Value Option In lieu of bifurcation, on an instrument-by-instrument basis, the Company may elect the fair value option for certain financial instruments that meet the required criteria under ASC 825, Financial Instruments . The Company elected the fair value option for both its legacy convertible notes and convertible 12% promissory notes, which met the required criteria under ASC 825, Financial Instruments . Interest expense associated with both the legacy convertible and convertible 12% promissory notes is included in the change in fair value of such instruments. Fair Value of Financial Instruments The Company accounts for the fair value of its financial instruments under the framework established by US GAAP which defines fair value and expands disclosures about fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The standard describes a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. Level 1 — Quoted prices in active markets for identical assets or liabilities the Company has the ability to access at the measurement date. Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of assets or liabilities. Level 3 — Pricing inputs that are unobservable, supported by little or no market activity and are significant to the fair value of the assets or liabilities. Transfers to/from Levels 1, 2, and 3 are recognized at the beginning of the reporting period. There were no transfers to/from Levels 1, 2, and 3 during three months ended March 31, 2024 and 2023 . ASC 820, Fair Value Measurement, states that in many cases, the transaction price will equal the fair value (for example, that might be the case when on the transaction date, the transaction to buy an asset takes place in the market in which the asset is sold). In determining whether a transaction price represents the fair value at initial recognition, the Company considers various factors such as whether the transaction was between related parties, is a forced transaction, or whether the unit of account for the transaction price does not represent the unit of account for the measured instrument. The Company does not measure assets at fair value on a recurring basis. The Company's liabilities that are measured at fair value on a recurring basis are its liability classified warrants, convertible 12% promissory notes, and forward purchase derivative liabilities. Refer to Note 9, Fair Value of Financial Instruments , for further discussion regarding the Company’s fair value measurements. The carrying value of the Company’s related party loans approximates fair value as the stated interest rate approximates market rates for similar loans and due to the short-term nature of such loans, which are due within three years or less from issuance. The carrying value of the Company’s cash, restricted cash, accounts payable, accrued expenses, bridge loans, convertible bridge loans, other current liabilities, and revolving line of credit approximates fair value primarily due to the short-term nature of such accounts. Leases The Company accounts for its leases under ASC 842, Leases . The operating lease right-of-use (“ ROU ”) asset represents the Company’s right to use an underlying asset during the lease term, and operating lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating leases are included in the ROU asset, current operating lease liabilities, and non-current operating lease liabilities in the accompanying condensed consolidated balance sheets. The operating lease ROU asset and lease liabilities are initially recognized based on the present value of the future minimum lease payments over the lease term at commencement date calculated using the Company’s incremental borrowing rate applicable to the lease asset, unless the implicit rate is readily determinable. The operating lease ROU asset also includes any lease payments made at or before lease commencement and exclude any lease incentives received. The Company determines the lease term as the noncancelable period of the lease and may include options to extend or terminate the lease when it is reasonably certain the Company will exercise that option. Leases with a term of 12 months or less are not recognized in the balance sheet. The Company’s leases do not contain any residual value guarantees. Lease expense for minimum lease payments is recognized as rent expense on a straight-line basis over the lease term. Operating expenses such as common area maintenance and utilities are treated as variable lease payments. Stock-Based Compensation Stock-based compensation expense is comprised of stock options awarded to employees and consultants. The Company accounts for share-based awards under the fair value method prescribed by ASC 718-10, Stock Compensation . The fair value of stock options is estimated using the Black-Scholes option pricing model on the date of grant. This option pricing model involves a number of estimates, including the per share value of the underlying common stock, exercise price, estimate of future volatility, expected term of the stock option award, risk-free interest rate and expected annual dividend yield. The fair value of the shares of common stock underlying the stock options has historically been determined by the Company’s board of directors as there was no public market for the underlying common stock prior to October 2, 2023. The Company’s board of directors determines the fair value of the Company’s common stock by considering a number of objective and subjective factors including contemporaneous third-party valuations of its common stock, the valuation of comparable companies, sales of the Company’s common stock to outside investors in arms-length transactions, the Company’s operating and financial performance, the lack of marketability, and general and industry specific economic outlook, and the implied fair values upon a merger transaction, amongst other factors. The Company recognizes the expense for options with graded-vesting schedules on a straight-line basis over the requisite service period, which is generally the vesting period. Forfeitures are recognized as they occur. Basic and Diluted Net Loss Per Common Share Basic net loss per common share is computed by dividing net loss for the year by the weighted-average number of common shares outstanding during the year. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding and potentially dilutive securities outstanding for the period using the treasury stock or if-converted method if their inclusion is dilutive. Diluted net loss per common share is the same as basic net loss per common share because the inclusion of potentially dilutive shares would be anti-dilutive to the calculation of net loss per common share. The Company has one class of shares issued and outstanding. Accordingly, basic and diluted net loss per share is not allocated among multiple classes of shares. Basic and diluted net loss per share for all periods prior to the Closing have been retrospectively adjusted by the Exchange Ratio to affect the reverse recapitalization. Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share for three months ended March 31, 2024 include the following: Private warrants 4,721,533 Working capital warrants 523,140 Public warrants 3,432,286 PIPE warrants 10,209,994 Stock options 1,969,261 SPA warrants 1,000,000 Senior convertible notes’ shares 1,000,000 Deferred founder shares (1) 1,173,631 Convertible bridge loan warrants 1,250,000 Convertible bridge loan consideration shares 7,334 Convertible bridge loans 619,146 Convertible 12% promissory note warrants 660,000 Convertible 12% promissory notes 367,850 Total 26,934,175 (1) As described in Note 8, Related Party Transactions , deferred founder shares do not have voting rights, do not participate in dividends and are not transferrable absent the Company’s consent. Therefore, while deferred founder shares are considered outstanding for legal purposes and are included in the total quantity of outstanding shares on the unaudited condensed consolidated statements of stockholders’ deficit, they are not considered outstanding for accounting purposes, including basic and diluted net loss per share purposes. Emerging Growth Company The Company is an “ Emerging Growth Company ,” as defined in Section 2(a) of the Securities Act, as modified by the Jumpstart our Business Startups Act of 2012, (the “ JOBS Act ”), and it may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies including, but not limited to, not being required to comply with the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act, reduced disclosure obligations regarding executive compensation in its periodic reports and proxy statements, and exemptions from the requirements of holding a nonbinding advisory vote on executive compensation and shareholder approval of any golden parachute payments not previously approved. Further, Section 102(b)(1) of the JOBS Act exempts emerging growth companies from being required to comply with new or revised financial accounting standards until private companies (that is, those that have not had a Securities Act registration statement declared effective or do not have a class of securities registered under the Exchange Act) are required to comply with the new or revised financial accounting standards. The JOBS Act provides that a company can elect to opt out of the extended transition period and comply with the requirements that apply to non-emerging growth companies but any such election to opt out is irrevocable. The Company has elected not to opt out of such extended transition period which means that when a standard is issued or revised and it has different application dates for public or private companies, the Company, as an emerging growth company, can adopt the new or revised standard at the time private companies adopt the new or revised standard. This may make comparison of the Company’s  unaudited condensed consolidated financial statements with another public company which is neither an emerging growth company nor an emerging growth company which has opted out of using the extended transition period difficult or impossible because of the potential differences in accounting standards used. Recently Issued Accounting Pronouncements Not Yet Adopted In December 2023 , the FASB issued ASU No. 2023-09, Improvements to Income Tax Disclosures (Topic 740) . The ASU requires disaggregated information about a reporting entity’s effective tax rate reconciliation as well as additional information on income taxes paid. The ASU is effective on a prospective basis for annual periods beginning after December 15, 2024. Early adoption is also permitted for annual financial statements that have not yet been issued or made available for issuance. This ASU will result in the required additional disclosures being included in the Company's unaudited condensed consolidated financial statements, once adopted. The Company is currently evaluating the impact of this standard on its financial statements and related disclosures.

Reverse Recapitalization

Reverse Recapitalization	3 Months Ended
	Mar. 31, 2024
Reverse Recapitalization [Abstract]
Reverse Recapitalization	Reverse Recapitalization As discussed in Note 1, Company Information , the Closing of the Business Combination occurred on September 29, 2023. In connection with the Business Combination: • All of Legacy NKGen’s legacy convertible notes were converted into shares of Legacy NKGen common stock immediately prior to Closing and pursuant to their terms, totaling 5,579,266 shares, which were then cancelled and converted into 2,278,598 shares of the Company’s common stock after giving effect to the Exchange Ratio; • All of Legacy NKGen’s 38,185,814 issued and outstanding shares were cancelled and converted into 15,595,262 shares of the Company’s common stock after giving effect to the Exchange Ratio (inclusive of shares attributable to the Legacy NKGen convertible notes); • All of Legacy NKGen’s 5,146,354 issued and outstanding stock options were cancelled and converted into 2,101,760 outstanding stock options of the Company; • The Company’s amended and restated certificate of incorporation and amended and restated bylaws were adopted; • The Company adopted an employee stock purchase plan; and • The Company adopted the 2024 equity incentive plan. The other related events that occurred in connection with the Closing include the following: • The execution of the private placement agreements, as described in Note 4, Private Placement ; • The assumption of the public and private warrants, as described in Note 5, Warrants ; • The execution of the warrant subscription agreements, as described in Note 5, Warrants ; • The conversion of Legacy NKGen’s legacy convertible notes, as described in Note 6, Convertible Notes ; • The execution of the securities purchase agreement, as described in Note 6, Convertible Notes ; and • The execution of the amended and restated sponsor support and lockup agreement, as described in Note 8, Related Party Transactions . Refer to Note 9, Fair Value of Financial Instruments , for the Company’s measurements with respect to the financial instruments issued in connection with the foregoing agreements. Legacy NKGen incurred $7.5 million of transaction costs in connection with the Business Combination, which was determined to be a capital-raising transaction for Legacy NKGen. Of the $7.5 million in transaction costs, $4.2 million and $3.3 million was allocated on a relative fair value basis to equity-classified instruments and liability-classified instruments, respectively. The following tables reconcile elements of the Business Combination to the Company’s unaudited condensed consolidated financial statements, and should be read in conjunction with the footnotes referenced above (in thousands, except share amounts): Shares Graf public shares, net of redemptions 93,962 Private placement investors’ shares 3,683,010 Graf founder shares 2,516,744 Total Graf shares outstanding immediately prior to the Business Combination 6,293,716 Conversion of Legacy NKGen convertible promissory notes (after the application of the Exchange Ratio) 2,278,598 Legacy NKGen rollover shares (after the application of the Exchange Ratio) 13,316,662 Total Legacy NKGen shares 15,595,260 Total Company common stock outstanding immediately following the Business Combination 21,888,976 (In thousands) Recapitalization Closing proceeds Proceeds from issuance of common stock $ 1,667 Proceeds from issuance of PIPE warrants 10,210 Proceeds from issuance of senior convertible promissory notes with warrants 10,000 Closing disbursements Less: Payment of Graf deferred underwriter fees (1,250) Less: Payment of Graf transaction costs at Closing (1) (7,456) Less: Payment of Legacy NKGen transaction costs at Closing (3,510) Net cash proceeds from the Business Combination at Closing $ 9,661 Less: Payment of Legacy NKGen transaction costs prior to Closing (2,089) Net cash proceeds from the Business Combination $ 7,572 Noncash activity Conversion of legacy NKGen convertible promissory notes 18,913 Less: Operating liabilities assumed from Graf (860) Less: Unpaid transaction costs – assumed from Graf (1) (5,400) Less: Unpaid transaction costs – Legacy NKGen (1,938) Liability-classified instruments Less: Fair value of PIPE warrants (10,210) Less: Fair value of forward purchase derivative liabilities (20,201) Less: Fair value of senior convertible promissory notes (2) (9,707) Less: Fair value of private warrants (1,841) Less: Fair value of working capital warrants (204) Net equity impact of the Business Combination $ (23,876) (1) The Graf transaction costs includes a $4.0 million accrual related to a certain vendor to be paid in cash and common stock of $2.0 million each. At Closing, a cash payment of $1.3 million was disbursed to this vendor. The remaining $2.7 million amount was recognized as a component of the unpaid transaction costs assumed from Graf, of which $0.7 million represents a cash settlement obligation, and the remaining $2.0 million represents an obligation to issue a variable number of shares for a fixed monetary amount which was accounted for as a liability under ASC 480, Distinguishing Liabilities from Equity (“ ASC 480 ”). Under ASC 480, the obligation to issue shares is not subsequently measured at fair value with changes recorded in earnings because the monetary amount is fixed. (2) Represents allocated fair value.

Private Placement

Private Placement	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Private Placement	Private Placement Initial Recognition Background Prior to the Closing, the Company entered into private agreements (“ Private Placement Agreements ”) with investors (“ FPA Investors ”) consisting of forward purchase agreements (“ Forward Purchase Agreements ”), subscription agreements, a side letter, and escrow agreements. The Private Placement Agreements closed on September 29, 2023. Pursuant to the Private Placement Agreements, the FPA Investors purchased 3,168,121 shares of common stock (“ FPA Shares ”) for $32.9 million (“ Prepayment Amount ”). The Prepayment Amount was deposited into escrow accounts. The terms of the Private Placement Agreements provide that following a one Measurement Period ”), funds in the escrow accounts may be released to the FPA Investors, the Company or a combination of both based on a combination of factors, including the volume weighted average price of the Company’s common stock (“ VWAP ”) over a specified valuation period during the Measurement Period (“ Reset Price ”), the number of shares sold by the FPA Investors during the Measurement Period, and the application of anti-dilution provisions. The Private Placement Agreements expire at the end of the Measurement Period. All funds in escrow will be released to the Company, the FPA Investors, or a combination of both, at or before the one year anniversary of the Closing. The maximum and minimum that could be released from escrow is the Prepayment Amount and zero, respectively, for both the FPA Investors and the Company. In addition, all interest earned on the funds in the escrow accounts will be released to the FPA Investors. During the Measurement Period, to the extent the Company’s share price approaches or exceeds $10.44 per share, the likelihood and amount of escrow funds to be released to the Company increases and the likelihood and amount of escrow funds to be released to the FPA Investors decreases. Conversely, during the Measurement Period, to the extent the Company’s share price decreases below $10.44 per share, the likelihood and amount of escrow funds to be released to the Company decreases and the likelihood and amount of escrow funds to be released to the FPA Investors increases. Other drivers of settlement outcomes include the number of shares sold by FPA Investors to third parties during the Measurement Period, whereby the selling of shares may decrease portions of escrow funds to be released to the FPA Investors by up to $2.00 per share sold, the application of antidilution provisions, the timing of sales and settlements, among other factors. Additionally, a prepayment shortfall of $0.1 million was established in connection with the Private Placement Agreements (“ Prepayment Shortfall ”). Pursuant to the terms and conditions of the Private Placement Agreements, sales of FPA Shares to third-parties are required to first be applied towards the Prepayment Shortfall prior to the subscription receivable (described further below). In addition to the FPA Shares, the FPA Investors received 514,889 shares of common stock for no incremental consideration (“ Bonus Shares ”). The Bonus Shares are not subject to an escrow arrangement. Accounting All FPA Shares and Bonus Shares are outstanding shares of the Company that are not held in escrow, are transferable without restrictions, and have the same voting as well as dividend and liquidation participation rights as other shares of the Company. Accordingly, such shares are equity classified and presented together with other shares of common stock in the unaudited condensed consolidated financial statements. The escrow agreements provide that funds placed into escrow are held in escrow for the benefit of the FPA Investors until they are released to the Company pursuant to the terms of the Private Placement Agreements and the Company’s creditors do not have access to the funds held in escrow in the event of bankruptcy of the Company. Accordingly, the Company accounted for the original Prepayment Amount of $32.9 million as a contra-equity subscription receivable because the funds held in escrow represent receivables from shareholders. The features of the Private Placement Agreements met the derivatives criteria under ASC 815 because they contained an underlying, notional amount, payment provision, and net settlement. Accordingly, a derivative liability was recognized based on the estimated measurement of the portion of the funds in escrow that could be released to the FPA Investors, based on circumstances existing as of Closing. The net balance of the Prepayment Amount presented as a subscription receivable and the derivative liability when considered together represents the estimated amount of escrow funds the Company expects to receive from the escrow accounts. Subsequent changes in fair value of the derivative liability associated with the Private Placement Agreements will be recognized through earnings on a quarterly basis. Upon the Closing, in addition to the $32.9 million subscription receivable, a loss on issuance of forward purchase contract totaling $24.5 million was recorded, which consisted of fair value of the derivative liabilities of $20.2 million plus the fair value of the Bonus Shares of $4.3 million. The forward purchase derivative liabilities are treated as a current liabilities because the Private Placement Agreements mature or otherwise are subject to early termination at or prior to the one year at or before the one year anniversary of the Closing. December 2023 Amendment On December 26, 2023, the Company and an FPA Investor entered into an amendment to their Forward Purchase Agreement (" December 2023 FPA Amendment ") for total proceeds of $0.5 million. No other Private Placement agreements were amended during the year ended December 31, 2023. The FPA Amendment provided that, (i) 200,000 FPA Shares were re-designated to Bonus Shares, (ii) the definition of Reset Price was changed (“ Amended Reset Price ”), (iii) the definition of the prepayment shortfall was amended (“ Amended Prepayment Shortfall ”), and (iv) the funds in the escrow account were transferred to a separate account held by the FPA Investor. The funds from the FPA Investor in connection with the amendment were not received by the Company until January 2024. The terms of the Amended Reset Price provide for (i) a rolling ceiling effective as of the FPA Amendment execution date based on a weekly trailing VWAP such that the Company does not benefit from increases in share price during the Measurement Period, and (ii) discounts of generally 10.0% to the VWAP measurement that benefit the FPA Investor. Proceeds from the sale of FPA Shares by FPA Investors to third parties are required to be treated as a reduction to the prepayment shortfall until no balance remains in the prepayment shortfall (“ Shortfall Sales ”), at which point proceeds from such sales of stock may be treated as reductions to the subscription receivable that may result in cash proceeds to the Company. If all FPA Shares are sold without full satisfaction of the prepayment shortfall, the Company is required, at their election, to either pay a cash amount equal to the remaining prepayment shortfall balance or issue additional shares at 90.0% of the VWAP for the trailing 20 trading days. The terms of the Amended Prepayment Shortfall provide for a $0.5 million increase to the FPA Investor’s pre-existing prepayment shortfall of $0.1 million. Upon execution of the FPA Amendment in December 2023, the Company recognized a loss on amendment to forward purchase contract as set forth below (in thousands): Loss on Amendment Reduction of subscription receivable $ 15,123 Change in fair value in connection with the amendment of forward purchase contracts (14,181) Cash received in connection with the amendments (500) Loss on amendment to forward purchase contracts $ 442 The $0.4 million loss recognized in connection with the FPA Amendment represents the reduction in cash proceeds the Company may receive under the forward purchase contract, partially offset by the reduction in the forward purchase derivative liabilities and the shareholder receivable. As a result of the FPA Amendment, the maximum cash proceeds the Company could receive under the forward purchase contract, reflected in the subscription receivable balance, was lowered. The reduction in the subscription receivable of $15.1 million was caused by (i) the Amended Reset Price, which reduced the maximum price per FPA Share the Company could receive (initially, $10.44 per share), (ii) the re-designation of 200,000 FPA Shares to Bonus Shares, reducing the total quantity of FPA Shares, and (iii) the Amended Prepayment Shortfall, which increased the prepayment shortfall amount. The Company does not receive any consideration for sales or settlements of Bonus Shares or Shortfall Sales, described further below. In addition to the reduction in the subscription receivable, the Company recognized a corresponding reduction in the fair value of the forward purchase derivative liabilities of $14.2 million . January and February 2024 Amendments From January to February 2024, the Company and certain FPA Investors entered into several additional amendments to the Forward Purchase Agreements (" 2024 FPA Amendments ") for total proceeds to the Company of $1.0 million. The 2024 FPA Amendments provided that, (i) 200,000 additional FPA Shares were re-designated to Bonus Shares, (ii) the definition of the prepayment shortfall consideration was further amended (“ 2024 Amended Prepayment Shortfall ”), and (iii) for the FPA Investor who was not party to the December 2023 FPA Amendment, the definition of Reset Price was changed (“ 2024 Amended Reset Price ”). The terms of the 2024 Amended Reset Price provide the FPA Investor (i) a rolling price per share effective as of the FPA Amendment execution date based on a weekly trailing VWAP, subject to a ceiling of $10.44 per share (" Initial Price ") , and (ii) discounts of generally 10.0% to the VWAP measurement that benefit the FPA Investor. The terms of the 2024 Amended Prepayment Shortfall provide for an aggregate $1.1 million increase to the FPA Investors’ pre-existing prepayment shortfall of $0.7 million. Upon execution of the 2024 FPA Amendments, the Company recognized a loss on amendment to forward purchase contract as set forth below (in thousands): Loss on Amendment Reduction of subscription receivable $ 2,764 Reduction in forward purchase derivative liabilities (1,418) Cash received in connection with the amendments (950) Loss on amendment to forward purchase contracts $ 396 The $0.4 million loss recognized in connection with the 2024 FPA Amendments represents the reduction in cash proceeds the Company may receive under the forward purchase contract, partially offset by the reduction in the forward purchase derivative liability and the shareholder receivable. As a result of the 2024 FPA Amendments, the maximum cash proceeds the Company could receive under the forward purchase contract, reflected in the subscription receivable balance, was lowered. The reduction in the subscription receivable of $2.8 million was caused by (i) the existing 2024 Amended Reset Price provisions as of the effective date of the 2024 FPA Amendments, (ii) the re-designation of 200,000 additional FPA Shares to Bonus Shares, further reducing the total quantity of FPA Shares outstanding, and (iii) the 2024 Amended Prepayment Shortfall, which increased the prepayment shortfall amount by an incremental $1.1 million . In addition to the reduction in the subscription receivable, the Company recognized a corresponding reduction in the fair value of the forward purchase derivative liabilities of $1.4 million . Sales of FPA Shares and Settlements of Forward Purchase Contracts Pursuant to the terms and conditions of the Private Placement Agreements, any sales of the Company’s common stock associated with the Private Placement Agreements may not be treated as sales of Bonus Shares until all FPA Shares are sold, at which point such sales of stock may be considered sales of Bonus Shares. As set forth above in this note, the forward purchase derivative liabilities represent the portion of the subscription receivable that may be released to the FPA Investors rather than the Company. Immediately prior to the settlement of a forward purchase contract, the derivative liability balance is adjusted to the applicable subscription receivable balance less the cash proceeds to be received as of the settlement date, recognized within the change in fair value of forward purchase derivative liabilities. Upon settlement of a forward purchase contract, the respective derivative liability and subscription receivable balances are derecognized and the cash proceeds to be received are recognized by the Company. Refer to Note 9, Fair Value of Financial Instruments , for further discussion. As of March 31, 2024, certain FPA Investors sold an aggregate of 1,768,121 shares of the Company’s common stock to third parties, representing all of the outstanding FPA Shares under the respective agreements. No other sales of FPA Shares occurred during the three months ended March 31, 2024. The following table summarizes the sales of FPA Shares and proceeds to the Company as of March 31, 2024 (in thousands): Sales of FPA Shares Total sales of FPA Shares $ 2,626 Shortfall Sales (1,753) Proceeds received from sales of FPA Shares $ 873 The following presents a reconciliation of the subscription receivable and forward purchase derivative liabilities during the three months ended March 31, 2024 (in thousands): Subscription Receivables Forward Purchase Derivative Liabilities Balance at December 31, 2023 $ 17,792 $ 15,804 Amendment of forward purchase contracts (2,764) (1,418) Change in fair value of forward purchase derivative liabilities — (535) Sales and settlement of forward purchase contracts (4,639) (3,766) Ending balance at March 31, 2024 $ 10,389 $ 10,085

Warrants

Warrants	3 Months Ended
	Mar. 31, 2024
Warrants [Abstract]
Warrants	Warrants As of March 31, 2024, all warrants described below remained outstanding and unexercised. Public Warrants In connection with Graf’s initial public offering (“ IPO ”), 3,432,286 warrants were issued to Graf’s investors (“ Public Warrants” ). The Public Warrants, which entitle th e registered holder to purchase one share of the Company’s common stock, have an exercise price of $11.50 per warrant, became exercisable 30 days after the completion of the Business Combination, and are set to expire five years from the completion of the Business Combination, or earlier upon redemption. The Public Warrants may be called for redemption at the sole discretion of the Company if the Company’s stock price equals or exceeds $18.00 per share and other certain conditions are met. The Public Warrants are equity classified due to terms indexed to the Company’s own stock and the satisfaction of other equity classification criteria. Private Warrants Concurrently with Graf’s IPO, Graf issued 4,721,533 warrants to Graf Acquisition Partners IV LLC (“ Private Warrants ”). The terms of the Private Warrants are identical to the Public Warrants with an exercise price of $11.50 per warrant, except that they are subject to certain transfer and sale restrictions and are not optionally redeemable so long as they are held by the initial purchasers or their permitted transferees. Additionally, the Private Warrants are exercisable on a cashless basis. If the Private Warrants are held by a party other than the initial purchasers or their permitted transferees, the Private Warrants will be redeemable by the Company and exercisable by such holders on the same basis as the Public Warrants. The Private Warrants are liability classified due to terms not indexed to the Company’s own stock. As described in Note 8, Related Party Transactions, the Private Warrants are a related party financial instrument. Private Warrants are classified to non-current liabilities because their term ends beyond one year from the latest unaudited condensed consolidated balance sheet date. SPA Warrants Together with the issuance of the Senior Convertible Notes described in Note 6, Convertible Notes , 1,000,000 warrants were issued to NKMAX at an exercise price of $11.50 per warrant (“ SPA Warrants ”). The terms of the SPA Warrants are identical to the terms of the Public Warrants with redemption at the sole discretion of the Company if the Company’s stock price equals or exceeds $18.00 per share and other certain conditions are met. The SPA Warrants are equity classified due to terms indexed to the Company’s own stock and the satisfaction of other equity classification criteria, including redemption in the Company’s control if the Company’s stock price equals or exceeds $18.00 per share. As described in Note 8, Related Party Transactions, the SPA Warrants are a related party financial instrument. Working Capital Warrants Prior to the Closing, Graf executed drawdowns upon a working capital loan facility. Upon Closing, the $0.8 million balance of the working capital loan facility was settled through the issuance of 523,140 warrants (“ Working Capital Warrants” ). The terms of the Working Capital Warrants are identical to the terms of the Private Warrants with an exercise price of $11.50 per warrant. The Working Capital Warrants are liability classified due to terms not indexed to the Company’s own stock. As described in Note 8, Related Party Transactions, the Working Capital Warrants are a related party financial instrument. Working Capital Warrants are classified to non-current liabilities because their term ends beyond one year from the latest unaudited condensed consolidated balance sheet date. PIPE Warrants Prior to the Closing, the Company entered into warrant subscription agreements (the “ Warrant Subscription Agreements ”) with certain investors (“ Warrant Investors ”), which closed on September 29, 2023. Pursuant to the Warrant Subscription Agreements, the Warrant Investors purchased an aggregate of 10,209,994 warrants, at a purchase price of $1.00 per warrant (“ PIPE Warrants ”) for total proceeds of $10.2 million. The PIPE Warrants are exercisable for cash (or by “cashless” exercise under certain circumstances) during the five-year period beginning on the Closing. One-third of the PIPE Warrants are exercisable initially at $10.00 per warrant, one-third of the PIPE Warrants are exercisable initially at $12.50 per warrant, and one-third of the PIPE Warrants are exercisable initially at $15.00 per warrant. The initial exercise prices of each tranche are subject to adjustment every 180 days after the Closing based upon declines in trading prices of the Company’s common stock, as well as antidilutive adjustments for stock splits, stock dividends, and the like. In addition, the PIPE Warrants contain a downside protection provision, pursuant to which the Warrant Investors may demand a cashless exchange of certain PIPE Warrants and, to the extent the relevant reference price is less than $1.50 per share, a cash payment calculated as the difference between $1.50 per share and the then-current exercise price multiplied by the applicable number of warrant shares shall be paid to the Warrant Investors. The PIPE Warrants are liability classified due to terms not indexed to the Company’s own stock and their cash settlement provisions. PIPE Warrants are classified to non-current liabilities because their term ends beyond one year from the latest unaudited condensed consolidated balance sheet date. PIPE Warrant Amendment On February 9, 2024 , the Company amended their Warrant Subscription Agreement with a Warrant Investor (" PIPE Warrant Amendment ") to, among other things, grant the Warrant Investor, (i) the right to exchange each PIPE Warrant for a newly registered share, effectively waiving the original strike price, (ii) a “Most Favored Nation” status with respect to warrant restructuring such that they may amend the terms upon the Company executing a similar transaction with more favorable terms for so long as any subscription warrants remain outstanding, and (iii) certain registration rights. In exchange, the Company received an upfront cash payment of $0.3 million and the right to receive a second cash payment of up to $0.3 million based on the trailing 5-day VWAP following the effective registration of the shares ("Deferred Payment"). The Deferred Payment is reflected within the fair value of the PIPE Warrant derivative liabilities under ASC 815, Derivatives and Hedging . All other terms and conditions remained unchanged. PIPE Warrant Amendment Cash proceeds $ 250 Reduction in PIPE Warrant derivative liability 429 Gain on amendment of PIPE warrant agreement $ 679 The reduction in the PIPE Warrant derivative liability was primarily attributable to the removal of the downside protection feature as well as the recognition of the Deferred Payment. Convertible Bridge Loan Warrants Together with the issuance of the Convertible Bridge Loans described in Note 6, Convertible Notes , 1,250,000 warrants were issued to lenders (“ Convertible Bridge Loan Warrants ”). The Convertible Bridge Loan Warrants, which entitle th e registered holder to purchase one share of the Company’s common stock, have an exercise price of $1.50 to $2.00 per warrant, became exercisable on the date of the issuance of the warrant , and are set to expire five years from issuance or earlier upon redemption. Additionally, the Convertible Bridge Loan Warrants are exercisable on a cashless basis if mutually agreed upon with the Company. Some of the warrants also have most favored nation status and reset provisions with respect to new warrant issues and existing warrant restructuring. The Convertible Bridge Loan Warrants are liability classified due to the Company not having a sufficient amount of authorized shares to satisfy the hypothetical conversion of the Convertible Bridge Loans as they do not contain a maximum number of shares that they are convertible into. Such warrants are classified to non-current liabilities because their term ends beyond one year from the latest unaudited condensed consolidated balance sheet date. Convertible 12% Promissory Note Warrants Together with the issuance of the Convertible 12% Promissory Notes described in Note 6, Convertible Notes , 660,000 warrants were issued to lenders (“ Convertible 12% Promissory Note Warrants ”). The terms of the Convertible 12% Promissory Note Warrants are identical to the Convertible Bridge Loan Warrants, as they entitle th e registered holder to purchase one share of the Company’s common stock, have an exercise price of $2.00 per warrant, became exercisable on the date of the issuance of the warrant , and are set to expire five years from issuance or earlier upon redemption. The Convertible 12% Promissory Note Warrants are liability classified due to the Company having an insufficient amount of authorized shares to satisfy the hypothetical conversion of the Convertible 12% Promissory Notes as they do not contain a maximum number of shares that they are convertible into. Such warrants are classified to non-current liabilities because their term ends beyond one year from the latest unaudited condensed consolidated balance sheet date.

Convertible Notes

Convertible Notes	3 Months Ended
	Mar. 31, 2024
Debt Disclosure [Abstract]
Convertible Notes	Convertible Notes Legacy Convertible Notes From November to December 2019 and from March to September 2023, the Company issued convertible promissory notes for aggregate proceeds of $17.3 million, of which $0.4 million were issued to related parties (“ Legacy Convertible Notes ”). The convertible notes issued during 2019 and 2023 bore an interest rate of 1.7% and 4.6% per year, respectively. Pursuant to their terms, immediately prior to Closing, all of the Legacy Convertible Notes were converted into 5,579,266 shares of Legacy NKGen common stock, which then converted into 2,278,598 shares of the Company’s common stock at Closing based on the Exchange Ratio. Senior Convertible Notes Prior to the Closing, the Company entered into convertible note subscription agreements (“ Securities Purchase Agreement ”) with NKMAX for total proceeds of $10.0 million , with a four -year term and an interest rate of 5.0% paid in cash semi-annually or 8.0% paid in kind (“ Senior Convertible Notes ”), which closed on September 29, 2023. Interest began accruing at Closing and is payable semi-annually in arrears, with interest that is paid in kind (if applicable) increasing the principal amount outstanding on each interest payment date. The Company currently expects to make their interest payments in-kind in lieu of periodic cash payments. The Senior Convertible Notes are convertible at any time, in whole or in part, at NKMAX’s option at a conversion price of $10.00 per share of common stock (subject to anti-dilution adjustments in the event of stock splits and the like). The Senior Convertible Notes have a put option which may be exercised by NKMAX 2.5 years after the issuance of the Senior Convertible Notes. No less than six months after exercise of the put option, the Company will be required to repay all principal and accrued interest of the Senior Convertible Notes. Should the put option remain unexercised, the outstanding principal and accrued interest will be due and payable on September 29, 2027. Additionally, as described in Note 5, Warrants , together with the Securities Purchase Agreement, the SPA Warrants were issued to NKMAX. Accordingly, a relative fair value allocation was applied and discount was recognized on the Senior Convertible Notes as set forth in Note 9, Fair Value of Financial Instruments . There are no financial or non-financial covenants associated with the Senior Convertible Notes. During the three months ended March 31, 2024, the Company recorded $0.2 million of interest expense and discount amortization related to the Senior Convertible Notes. As described in Note 8, Related Party Transactions, the Senior Convertible Notes are a related party financial instrument. The following table presents a reconciliation of the Senior Convertible Notes (in thousands): Senior Convertible Balance as of December 31, 2023 $ 9,930 Amortization of discount 11 Paid-in-kind interest 206 Balance as of March 31, 2024 $ 10,147 Convertible Bridge Loans From February to March 2024 , the Company issued convertible bridge loans to holders (" 2024 Convertible Bridge Loans ") and related parties (" 2024 Related Party Convertible Bridge Loan "), collectively referred to as (" Convertible Bridge Loans ") for total proceeds of $0.3 million and $0.4 million, respectively, with a 20.0% premium due at maturity. The Convertible Bridge Loans mature at the earlier of (i) 60 days from the respective issuance dates, (ii) upon a financing event with third parties exceeding between $5.0 million and $10.0 million, depending on the agreement, (iii) the occurrence of any event of default, or (iv) the acceleration of the short term bridge note. The loans are convertible at any time, in whole or in part, at the holder's option into the Company's common stock at a 15.0% discount to the VWAP 10 days prior to conversion, with the conversion being limited to converting at no more than $2.00 per share. Certain Convertible Bridge Loans also entitle the holder to 7,334 shares of the Company's common stock (“ Consideration Shares ”). Consideration Shares are liability classified until issuance due to the insufficiency of authorized and unissued shares. Additionally, as described in Note 5, Warrants , concurrently with the Convertible Bridge Loans, the Company issued the Convertible Bridge Loan Warrants to holders which were recognized at fair value of $1.4 million. There are no other financial or non-financial covenants associated with the Convertible Bridge Loans. The Company recognized a loss of $0.7 million upon issuance of the Convertible Bridge Loans, Convertible Bridge Loan Warrants and Consideration Shares representing the excess of the $1.4 million initial fair value of the Convertible Bridge Loan Warrants over the $0.7 million proceeds received. Accordingly, a discount was recognized on the Convertible Bridge Loans. Refer to Note 9, Fair Value of Financial Instrument s. The Company accretes the balance of the Convertible Bridge Loans on a straight-line basis to its repayment amount through interest expense. During the three months ended March 31, 2024, the Company recorded $0.2 million of interest expense and discount amortization related to the 2024 Convertible Bridge Loans and $0.4 million interest expense and discount amortization related to the 2024 Related Party Convertible Bridge Loan. As of March 31, 2024, $0.2 million remained to be accreted through interest expense on the Convertible Bridge Loans. No interest expense was incurred for the Convertible Bridge Loans during the three months ended March 31, 2023. In April 2024, the outstanding principal and interest of two of the 2024 Convertible Bridge Loans and the 2024 Related Party Convertible Bridge Loan were repaid in full, for an aggregate payment of $0.3 million and $0.5 million , respectively. On April 19, 2024, one of the Convertible Bridge Loans was amended to extend the maturity date to be the earliest of (i) 90 days from issuance, (ii) upon a financing event with third parties exceeding $5.0 million, (iii) the occurrence of any event of default, or (iv) the acceleration of the amended and restated short term bridge note. On April 25, 2024, $0.1 million, representing a portion of the outstanding balance was repaid to the lender with less than $0.1 million remaining outstanding under the related Convertible Bridge Loan. Convertible 12% Promissory Notes In March 2024 , the Company issued convertible 12% promissory notes (" Convertible 12% Promissory Notes ") to two holders, one of which is an FPA Investor, with a one year term, for total proceeds of $0.6 million and an original issue discount of $0.1 million. The first 12 months of interest is due and payable as of each respective issuance date. All or any portion of the then outstanding and unpaid principal amount and interest of the Convertible 12% Promissory Notes are convertible at any time at the holder's option into the Company's common stock at a conversion price of $2.00 per share. The Company also issued 500,000 shares of the Company's common stock to holders. Concurrently with the issuance of the Convertible 12% Promissory Notes, the Convertible 12% Promissory Note Warrants were issued to holders, as described in Note 5, Warrants . The Company elected to measure the Convertible 12% Promissory Notes, including accrued interest, using the fair value option under ASC 825, Financial Instruments . Changes in fair value are included in change in fair value of Convertible 12% Promissory Notes on the unaudited condensed consolidated statements of operations. See Note 9, Fair Value of Financial Instrument s, for further information. There are no financial or non-financial covenants associated with the Convertible 12% Promissory Notes . During the three months ended March 31, 2024, the Company recorded a change in fair value of Convertible 12% Promissory Notes of $0.5 million related to the Convertible 12% Promissory Notes. On April 8, 2024 and May 9, 2024 both of the Convertible 12% Promissory Notes were repaid in full for an aggregate repayment of $0.8 million . Debt Revolving Line of Credit In June 2023, the Company entered into a $5.0 million revolving line of credit agreement (as amended on September 19, 2023, January 30, 2024 and April 5, 2024) with a commercial bank with a one-year term and an interest rate based on the higher of (i) the one month secured overnight financing rate plus 2.9% or (ii) 7.5%. Issuance fees of $0.1 million were incurred in connection with this revolving line of credit. All outstanding balances under the revolving line of credit were due and payable on June 20, 2024. In April 2024, the agreement was amended to extended the maturity date of the revolving line of credit to September 18, 2024. The revolving line of credit is secured by all of the Company’s assets, including a deed of trust over the Company’s owned real property located in Santa Ana, California. The Company was required to maintain deposits with the lender in an amount of at least $15.0 million from a certain period of time as long as there was a debt balance outstanding. Pursuant to a letter of intent signed in March 2024, in April 2024, the lender subsequently waived the minimum cash deposit requirement in exchange for a $0.1 million payment and the Company's agreement to use the lender as their primary banking relationship. The Company was in compliance with its debt covenants as of March 31, 2024. Additionally, the Company is required to maintain a restricted cash balance of $0.3 million following the issuance. As of March 31, 2024, the interest rate for the revolving line of credit was 8.2%. Through March 31, 2024, the Company drew down $4.9 million upon the revolving line of credit and no repayments of drawdowns occurred. Interest expense of $0.1 million was incurred upon the revolving line of credit, which was paid in cash during the three months ended March 31, 2024. No interest expense was incurred for the revolving line of credit during the three months ended March 31, 2023 as it was not outstanding. Related Party Loans Between August 2019 and April 2023, the Company entered into related party loans with NKMAX (“ Related Party Loans ”). From January through April 2023, the Company entered into additional Related Party Loans with NKMAX for aggregate gross proceeds of $5.0 million. These additional Related Party Loans bear an interest rate of 4.6% and mature on December 31, 2024. There are no financial or non-financial covenants associated with the Related Party Loans. The additional Related Party Loans are not convertible into equity. In connection with the Related Party Loans, interest expenses incurred were $0.1 million and less than $0.1 million for the three months ended March 31, 2024 and 2023, respectively. Related party interest payable amounts recorded to other current liabilities on the unaudited condensed consolidated balance sheets were $0.1 million and $0.2 million as of March 31, 2024 and December 31, 2023, respectively. Bridge Loans In March 2024 , the Company entered into bridge loan agreements (" Bridge Loans ") for total proceeds of $0.2 million, with a premium of 7.5% of the principal , and a maturity date 15 days from funding. The bridge loans were subsequently paid in full on April 10, 2024 .

Debt

Debt	3 Months Ended
	Mar. 31, 2024
Debt Disclosure [Abstract]
Debt	Convertible Notes Legacy Convertible Notes From November to December 2019 and from March to September 2023, the Company issued convertible promissory notes for aggregate proceeds of $17.3 million, of which $0.4 million were issued to related parties (“ Legacy Convertible Notes ”). The convertible notes issued during 2019 and 2023 bore an interest rate of 1.7% and 4.6% per year, respectively. Pursuant to their terms, immediately prior to Closing, all of the Legacy Convertible Notes were converted into 5,579,266 shares of Legacy NKGen common stock, which then converted into 2,278,598 shares of the Company’s common stock at Closing based on the Exchange Ratio. Senior Convertible Notes Prior to the Closing, the Company entered into convertible note subscription agreements (“ Securities Purchase Agreement ”) with NKMAX for total proceeds of $10.0 million , with a four -year term and an interest rate of 5.0% paid in cash semi-annually or 8.0% paid in kind (“ Senior Convertible Notes ”), which closed on September 29, 2023. Interest began accruing at Closing and is payable semi-annually in arrears, with interest that is paid in kind (if applicable) increasing the principal amount outstanding on each interest payment date. The Company currently expects to make their interest payments in-kind in lieu of periodic cash payments. The Senior Convertible Notes are convertible at any time, in whole or in part, at NKMAX’s option at a conversion price of $10.00 per share of common stock (subject to anti-dilution adjustments in the event of stock splits and the like). The Senior Convertible Notes have a put option which may be exercised by NKMAX 2.5 years after the issuance of the Senior Convertible Notes. No less than six months after exercise of the put option, the Company will be required to repay all principal and accrued interest of the Senior Convertible Notes. Should the put option remain unexercised, the outstanding principal and accrued interest will be due and payable on September 29, 2027. Additionally, as described in Note 5, Warrants , together with the Securities Purchase Agreement, the SPA Warrants were issued to NKMAX. Accordingly, a relative fair value allocation was applied and discount was recognized on the Senior Convertible Notes as set forth in Note 9, Fair Value of Financial Instruments . There are no financial or non-financial covenants associated with the Senior Convertible Notes. During the three months ended March 31, 2024, the Company recorded $0.2 million of interest expense and discount amortization related to the Senior Convertible Notes. As described in Note 8, Related Party Transactions, the Senior Convertible Notes are a related party financial instrument. The following table presents a reconciliation of the Senior Convertible Notes (in thousands): Senior Convertible Balance as of December 31, 2023 $ 9,930 Amortization of discount 11 Paid-in-kind interest 206 Balance as of March 31, 2024 $ 10,147 Convertible Bridge Loans From February to March 2024 , the Company issued convertible bridge loans to holders (" 2024 Convertible Bridge Loans ") and related parties (" 2024 Related Party Convertible Bridge Loan "), collectively referred to as (" Convertible Bridge Loans ") for total proceeds of $0.3 million and $0.4 million, respectively, with a 20.0% premium due at maturity. The Convertible Bridge Loans mature at the earlier of (i) 60 days from the respective issuance dates, (ii) upon a financing event with third parties exceeding between $5.0 million and $10.0 million, depending on the agreement, (iii) the occurrence of any event of default, or (iv) the acceleration of the short term bridge note. The loans are convertible at any time, in whole or in part, at the holder's option into the Company's common stock at a 15.0% discount to the VWAP 10 days prior to conversion, with the conversion being limited to converting at no more than $2.00 per share. Certain Convertible Bridge Loans also entitle the holder to 7,334 shares of the Company's common stock (“ Consideration Shares ”). Consideration Shares are liability classified until issuance due to the insufficiency of authorized and unissued shares. Additionally, as described in Note 5, Warrants , concurrently with the Convertible Bridge Loans, the Company issued the Convertible Bridge Loan Warrants to holders which were recognized at fair value of $1.4 million. There are no other financial or non-financial covenants associated with the Convertible Bridge Loans. The Company recognized a loss of $0.7 million upon issuance of the Convertible Bridge Loans, Convertible Bridge Loan Warrants and Consideration Shares representing the excess of the $1.4 million initial fair value of the Convertible Bridge Loan Warrants over the $0.7 million proceeds received. Accordingly, a discount was recognized on the Convertible Bridge Loans. Refer to Note 9, Fair Value of Financial Instrument s. The Company accretes the balance of the Convertible Bridge Loans on a straight-line basis to its repayment amount through interest expense. During the three months ended March 31, 2024, the Company recorded $0.2 million of interest expense and discount amortization related to the 2024 Convertible Bridge Loans and $0.4 million interest expense and discount amortization related to the 2024 Related Party Convertible Bridge Loan. As of March 31, 2024, $0.2 million remained to be accreted through interest expense on the Convertible Bridge Loans. No interest expense was incurred for the Convertible Bridge Loans during the three months ended March 31, 2023. In April 2024, the outstanding principal and interest of two of the 2024 Convertible Bridge Loans and the 2024 Related Party Convertible Bridge Loan were repaid in full, for an aggregate payment of $0.3 million and $0.5 million , respectively. On April 19, 2024, one of the Convertible Bridge Loans was amended to extend the maturity date to be the earliest of (i) 90 days from issuance, (ii) upon a financing event with third parties exceeding $5.0 million, (iii) the occurrence of any event of default, or (iv) the acceleration of the amended and restated short term bridge note. On April 25, 2024, $0.1 million, representing a portion of the outstanding balance was repaid to the lender with less than $0.1 million remaining outstanding under the related Convertible Bridge Loan. Convertible 12% Promissory Notes In March 2024 , the Company issued convertible 12% promissory notes (" Convertible 12% Promissory Notes ") to two holders, one of which is an FPA Investor, with a one year term, for total proceeds of $0.6 million and an original issue discount of $0.1 million. The first 12 months of interest is due and payable as of each respective issuance date. All or any portion of the then outstanding and unpaid principal amount and interest of the Convertible 12% Promissory Notes are convertible at any time at the holder's option into the Company's common stock at a conversion price of $2.00 per share. The Company also issued 500,000 shares of the Company's common stock to holders. Concurrently with the issuance of the Convertible 12% Promissory Notes, the Convertible 12% Promissory Note Warrants were issued to holders, as described in Note 5, Warrants . The Company elected to measure the Convertible 12% Promissory Notes, including accrued interest, using the fair value option under ASC 825, Financial Instruments . Changes in fair value are included in change in fair value of Convertible 12% Promissory Notes on the unaudited condensed consolidated statements of operations. See Note 9, Fair Value of Financial Instrument s, for further information. There are no financial or non-financial covenants associated with the Convertible 12% Promissory Notes . During the three months ended March 31, 2024, the Company recorded a change in fair value of Convertible 12% Promissory Notes of $0.5 million related to the Convertible 12% Promissory Notes. On April 8, 2024 and May 9, 2024 both of the Convertible 12% Promissory Notes were repaid in full for an aggregate repayment of $0.8 million . Debt Revolving Line of Credit In June 2023, the Company entered into a $5.0 million revolving line of credit agreement (as amended on September 19, 2023, January 30, 2024 and April 5, 2024) with a commercial bank with a one-year term and an interest rate based on the higher of (i) the one month secured overnight financing rate plus 2.9% or (ii) 7.5%. Issuance fees of $0.1 million were incurred in connection with this revolving line of credit. All outstanding balances under the revolving line of credit were due and payable on June 20, 2024. In April 2024, the agreement was amended to extended the maturity date of the revolving line of credit to September 18, 2024. The revolving line of credit is secured by all of the Company’s assets, including a deed of trust over the Company’s owned real property located in Santa Ana, California. The Company was required to maintain deposits with the lender in an amount of at least $15.0 million from a certain period of time as long as there was a debt balance outstanding. Pursuant to a letter of intent signed in March 2024, in April 2024, the lender subsequently waived the minimum cash deposit requirement in exchange for a $0.1 million payment and the Company's agreement to use the lender as their primary banking relationship. The Company was in compliance with its debt covenants as of March 31, 2024. Additionally, the Company is required to maintain a restricted cash balance of $0.3 million following the issuance. As of March 31, 2024, the interest rate for the revolving line of credit was 8.2%. Through March 31, 2024, the Company drew down $4.9 million upon the revolving line of credit and no repayments of drawdowns occurred. Interest expense of $0.1 million was incurred upon the revolving line of credit, which was paid in cash during the three months ended March 31, 2024. No interest expense was incurred for the revolving line of credit during the three months ended March 31, 2023 as it was not outstanding. Related Party Loans Between August 2019 and April 2023, the Company entered into related party loans with NKMAX (“ Related Party Loans ”). From January through April 2023, the Company entered into additional Related Party Loans with NKMAX for aggregate gross proceeds of $5.0 million. These additional Related Party Loans bear an interest rate of 4.6% and mature on December 31, 2024. There are no financial or non-financial covenants associated with the Related Party Loans. The additional Related Party Loans are not convertible into equity. In connection with the Related Party Loans, interest expenses incurred were $0.1 million and less than $0.1 million for the three months ended March 31, 2024 and 2023, respectively. Related party interest payable amounts recorded to other current liabilities on the unaudited condensed consolidated balance sheets were $0.1 million and $0.2 million as of March 31, 2024 and December 31, 2023, respectively. Bridge Loans In March 2024 , the Company entered into bridge loan agreements (" Bridge Loans ") for total proceeds of $0.2 million, with a premium of 7.5% of the principal , and a maturity date 15 days from funding. The bridge loans were subsequently paid in full on April 10, 2024 .

Related-Party Transactions

Related-Party Transactions	3 Months Ended
	Mar. 31, 2024
Related Party Transactions [Abstract]
Related-Party Transactions	Related Party Transactions Founder Shares Contemporaneously with the execution of the Merger Agreement, Graf and NKGen entered into an amended and restated sponsor support and lockup agreement (“ Amended and Restated Sponsor Support and Lockup Agreement ”). In connection with the Amended and Restated Sponsor Support and Lockup Agreement, of the 4,290,375 shares of Graf formerly held by Graf’s sponsor and insiders (“ Founder Shares ”): (i) 1,773,631 shares were forfeited, (ii) 1,173,631 shares became restricted shares subject to vesting conditions (“ Deferred Founder Shares ”), and (iii) the remaining 1,343,113 shares are subject to trading restrictions for up to two years and continue to be outstanding and fully vested shares. Deferred Founder Shares do not have voting rights, do not participate in dividends and are not transferable. During the vesting period of five years from Closing (“ Vesting Period ”), if the trading price or price per share consideration upon a change in control for common stock is greater than or equal to $14.00 at any 20 trading days in a 30 consecutive trading-day period, then 873,631 Deferred Founder Shares will immediately vest; and if greater than or equal to $20.00 at any 20 trading days in a 30 consecutive trading-day period, then an additional 300,000 Deferred Founder Shares will immediately vest. In the event there is a sale of the Company, then immediately prior to the consummation of such sale, the calculated Acquiror Sale Price, as defined in the agreement, will take into account the number of Deferred Founder Shares that will vest upon a change in control. Upon the expiration of the Vesting Period, unvested Founder Shares will be forfeited and cancelled for no consideration. All Founder Shares, including Deferred Founder Shares, are equity classified primarily due to terms indexed to the Company’s own stock, including upon a change in control. Related Party Financial Instruments The Company’s related party financial instruments include (i) the Founder Shares, including Deferred Founder Shares described above in this Note 8, (ii) the SPA Warrants described in Note 5, Warrants , (iii) the Working Capital Warrants described in Note 5, Warrants , (iv) the Senior Convertible Notes described in Note 6, Convertible Notes , (v) 2024 Related Party Convertible Bridge Loan described in Note 6, Convertible Notes, (vi) select Legacy Convertible Notes described in Note 6, Convertible Notes , (vii) the Related Party Loans described in Note 7, Debt , (viii) the Private Warrants described in Note 5, Warrants , and (ix) 400,000 Convertible Bridge Warrants described in Note 5, Warrants . Purchases of laboratory supplies For the three months ended March 31, 2024 and 2023 , the Company did not record any research and development expenses associated with the purchase of laboratory supplies from NKMAX. As of March 31, 2024 no amounts payable remained outstanding relating to the purchase of laboratory supplies. As of December 31, 2023 , $0.6 million remained outstanding relating to the purchase of laboratory supplies from NKMAX, which were recorded to accounts payable and accrued expenses on the consolidated balance sheets.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company accounts for the fair value of its financial instruments under the framework established by US GAAP which defines fair value and expands disclosures about fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The standard describes a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value. The Company’s management used the following methods and assumptions to estimate the fair value of its financial instruments: Level 1 — Quoted prices in active markets for identical assets or liabilities the Company has the ability to access at the measurement date. Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of assets or liabilities. Level 3 — Pricing inputs that are unobservable, supported by little or no market activity and are significant to the fair value of the assets or liabilities. The carrying amounts of the Company’s financial assets and financial liabilities are considered to be representative of their respective fair values because of the short-term nature of those instruments. The Company does not measure assets at fair value on a recurring basis. Liabilities measured at fair value on a recurring basis as of March 31, 2024 are as follows (in thousands):  Fair Value Measurements at Reporting Date Using Balance as of Level 1 Level 2 Level 3 Convertible 12% Promissory Notes $ 728 $ — $ — $ 728 Private Warrants 803 — — 803 Working Capital Warrants 89 — — 89 PIPE Warrants 19,704 — — 19,704 Convertible Bridge Loan Warrants 1,822 — — 1,822 Convertible 12% Promissory Note Warrants 942 — — 942 Forward Purchase Derivative Liabilities 10,085 — — 10,085 Consideration Shares 14 14 — — Total $ 34,187 $ 14 $ — $ 34,173 In addition to items that are measured at fair value on a recurring basis, the Company also has liabilities that are measured at fair value on a nonrecurring basis and therefore are not included in the tables above. Liabilities that are measured at fair value on a nonrecurring basis as of March 31, 2024 include the Senior Convertible Notes. The Senior Convertible Notes were determined to be in-scope of ASC 470, Debt . Accordingly, this instrument will not be measured at fair value on a recurring basis as the fair value measurement of this instrument was for purposes of the relative fair value allocation as the Senior Convertible Notes were issued together with the SPA Warrants. Legacy Convertible Notes For the three months ended March 31, 2023, the Company recognized $1.5 million of expense associated with the change in fair value of the Legacy Convertible Notes. The Legacy Convertible Notes converted at Closing on September 29, 2023. The fair value of the notes immediately prior to their conversion at Closing was based upon the fair value of the 2,278,598 shares of the Company’s common stock issued upon their conversion totaling $18.9 million, at a per share value of $8.30 based upon the fair value of the Company’s common stock at Closing. Convertible 12% Promissory Notes The following table presents a reconciliation of the Convertible 12% Promissory Notes (in thousands): Convertible 12% Promissory Notes Balance as of December 31, 2023 $ — Issuance 250 Change in fair value $ 478 Balance as of March 31, 2024 $ 728 The fair value of the Convertible 12% Promissory Notes was measured using a binomial lattice model. A binomial stock lattice model generates two probable outcomes of stock price -one up and another down -emanating at each point in time or "node", starting from the valuation date until the maturity date. This lattice generates a distribution of stock price. Based on the stock price at each corresponding node, the value of the Notes was determined by evaluating the optimal decision that a holder and/or the issuer would make to maximize its payoff (the "Decision Tree"). At maturity, the value of the notes was calculated as the maximum between the principal amount and the conversion value. At each node prior to maturity, the lattice model determines whether the notes would be (i) converted by the holder, or (ii) held by the holder, based on the payoff related to each decision. Volatility in the model was estimated from historical equity volatility, median asset volatility of comparable companies, and was adjusted using the Company's capital structure. The cost of debt used in discounting the Notes was estimated based on (i) market yield curve corresponding to the estimated synthetic credit rating of the Company, and (ii) observed market spreads of publicly traded comparable debt with similar credit rating and industry as that of the Company. The following unobservable assumptions were used in determining the fair value of the Convertible 12% Promissory Notes at March 31, 2024: Credit spread 27.5 % Equity volatility 45.0 % Liability Classified Warrants The following table represent a reconciliation of all liability classified warrants (in thousands): Private Warrants Working Capital Warrants Convertible Bridge Loan Warrants Convertible 12% Promissory Note Warrants PIPE Warrants Total Balance December 31, 2023 $ 377 $ 42 $ — $ — $ 25,339 $ 25,758 Issuances — — 1,424 323 — 1,747 Change in fair value in connection with PIPE Warrants Amendment — — — — (429) (429) Change in fair value 426 47 398 619 (5,206) (3,716) Balance as of March 31, 2024 $803 $89 $1,822 $942 $ 19,704 $ 23,360 The fair value of the Private Warrants, Working Capital Warrants, Convertible Bridge Loan Warrants, and Convertible 12% Promissory Note Warrants were measured using a Black-Scholes model. The estimated fair value of the liability classified warrants was determined using Level 3 inputs. Inherent in a Black-Scholes model are assumptions related to expected stock-price volatility, expected life, risk-free interest rate and dividend yield. The Company estimates the volatility of its liability classified warrants based on implied volatility from the Company’s traded warrants and from historical volatility of select peer company’s common stock that matches the expected remaining life of each class of warrants as well as historical volatility of select peer company’s traded options. The risk-free interest rate is based on the U.S. Treasury zero-coupon yield curve on the grant date for a maturity similar to the expected remaining life of each class of warrants. The expected life of each class of warrants is assumed to be equivalent to their remaining contractual term. The dividend rate is based on the historical rate, which the Company anticipates remaining at zero. The fair value of the PIPE Warrants was valued using level three inputs and was estimated using a Monte Carlo simulation approach. The Company’s common share price was assumed to follow a Geometric Brownian Motion over a period from the Valuation Date to the Expiration Date. The breadth of all possible scenarios was captured in an estimate of volatility, based on comparable companies’ historical equity volatilities, considering differences in their capital structure. For each simulation path, the test price and Reset Price were calculated based on the daily stock price during the measurement period. On each reset date, the downside protection condition was assessed to see if it was met by comparing the test price with the downside protection threshold price. The value of each tranche of warrants was then computed, factoring in any downside protection shares and downside protection cash, if applicable. The average value across this range of possible scenarios, discounted to present using the risk-free rate, was used as the fair value of the PIPE Warrants. The change in fair value of the PIPE Warrants was primarily attributable to select features of the Warrant Subscription Agreements, including strike price resets and downside protection which results in decreased value as the Company’s stock price volatility increases and the stock price declines. The following unobservable assumptions were used in determining the fair value of the liability classified warrants at March 31, 2024 and December 31, 2023: At March 31, 2024 At December 31, 2023 or closing date if later Private Warrants and Working Capital Warrants Private Warrants’ volatility 55.5 % 35.3 % Dividend yield (per share) — — Convertible Bridge Loan Warrants Volatility 100.0 % 105.0 % Dividend yield (per share) — — Convertible 12% Promissory Note Warrants Equity volatility 100.0 % — PIPE Warrants Credit spread 19.0 % 12.7 % Equity volatility 105.0 % 100.0 % The following unobservable assumptions were used in determining the fair value of the PIPE Warrants immediately before and after modification at February 9, 2024: Credit spread 17.8 % Equity volatility 105.0 % Forward Purchase Derivative Liabilities The forward purchase derivative liabilities were recognized at Closing on September 29, 2023. The fair value as of March 31, 2024 was $10.1 million. Refer to Note 4, Private Placements , for a reconciliation of the forward purchase derivative liabilities. The fair value of the forward purchase derivative liabilities was estimated using a Monte Carlo simulation approach. The Company’s common share price was simulated with daily time steps for a range of various possible scenarios. The breadth of all possible scenarios was captured in an estimate of volatility, based on comparable companies’ historical equity volatilities, considering differences in their capital structure. The simulated prices were compared against the settlement adjustment features of the Forward Purchase Agreements. Under each simulated scenario of future stock price, the Company calculated the value of the forward purchase derivative liability arrangement. The average value across this range of possible scenarios, discounted to present using the risk-free rate, was used as the fair value of the forward purchase derivative liabilities. The following unobservable assumptions were used in determining the fair value of the forward purchase derivative liabilities at the respective balance sheet and amendment dates: March 31, 2024 February 21, 2024 January 19, 2024 December 31, 2023 Dividend yield 0.0 % 0.0 % 0.0 % 0.0 % Equity volatility 120.0 % 145.0 % 105.0 % 115.0 % Consideration Shares The Consideration Shares are recorded at fair value on a recurring basis within Accounts payable and accrued expenses. These shares are liability-classified until issuance and relate to the Convertible Bridge Loans. The liability associated with these Consideration Shares is carried at fair value, demonstrating the obligation to the lenders. The estimated fair value of the Consideration Shares is based on quoted market prices that are readily and regularly available in an active market. Relative Fair Values The Convertible 12% Promissory Notes were issued together with the Convertible 12% Promissory Note Warrants. Thus, each instrument was recorded at its fair value, limited to a relative fair value based upon the percentage of its fair value to the total fair value based on the transaction price of $0.6 million at issuance. The Company elected to record the Convertible 12% Promissory Notes at fair value under ASC 825, Financial Instruments . The relative fair value at initial recognition for the Convertible 12% Promissory Notes and Convertible 12% Promissory Note Warrants was $0.3 million and $0.3 million, respectively. The stand-alone fair value of the Convertible 12% Promissory Notes and Convertible 12% Promissory Note Warrants was $0.7 million and $0.9 million as of March 31, 2024. Residual Fair Values The Convertible Bridge Loans were issued together with the Convertible Bridge Loan Warrants. The Convertible Bridge Loan Warrants were recorded at fair value, under ASC 815, Derivatives and Hedging , and the Convertible Bridge Loans were determined to be in-scope of 470, Debt . Accordingly, the Company recorded the fair value of the Convertible Bridge Loan Warrants at issuance, with the residual amount of the proceeds allocated to the convertible debt instrument.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Stockholders' Equity	Stockholder’s Equity Reverse Recapitalization As described in Note 2, Summary of Significant Accounting Policies , all historical equity data, including stock option data, in these unaudited condensed consolidated financial statements has been retrospectively adjusted by the Exchange Ratio to reflect the reverse recapitalization that occurred on September 29, 2023. Common Stock As of March 31, 2024, the Company had authorized 500,000,000 shares of common stock, par value $0.0001 per share. As of March 31, 2024, 22,388,976 shares of common stock were issued and outstanding, and 477,611,024 shares of common stock were reserved for future issuance. Preferred Stock As of March 31, 2024, the Company had authorized 10,000,000 shares of preferred stock, par value $0.0001. As of March 31, 2024, zero shares of preferred stock were issued or outstanding. Employee Stock Purchase Plan Upon consummation of the Business Combination, the Company adopted an employee stock purchase plan (“ ESPP ”). The maximum number of shares of the Company’s common stock that may be issued under the ESPP is 3.0% of the fully diluted common stock of the Company, determined as of immediately following Closing. Such maximum number of shares is subject to automatic annual increases. The Company’s employees and the employees of any designated affiliates may participate in the ESPP. The purchase price of the ESPP shares is 85.0% of the lesser of the fair market value of the Company’s common stock on the first day of an offering or on the applicable date of purchase. As of March 31, 2024, there were no transactions with respect to the ESPP.  2019 Plan The Company’s 2019 Plan ( “2019 Plan” ) became effective on October 23, 2019. The 2019 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock unit awards and performance share awards to employees, directors, and consultants of the Company. As of March 31, 2024, the Company has only issued stock options. Stock options granted under the 2019 Plan expire no later than ten years from the date of grant and generally vest over a four three 2023 Plan Upon consummation of the Business Combination, the Company adopted the 2023 equity incentive plan (“ 2023 Plan ”). The maximum number of shares of common stock that may be issued under the 2023 Plan is 12.0% of the fully diluted common stock of the Company, determined as of immediately following Closing. Such maximum number of shares is subject to automatic annual increases. Under the 2023 Plan, restricted shares and stock options with service or performance based conditions may be granted to employees and nonemployees. Upon the effective date of the 2023 Plan, the Company may not grant any additional awards under the 2019 Plan. As of March 31, 2024, certain awards to executives and non-employee directors were granted under the 2023 Plan. Stock options granted under the 2023 Plan expire no later than ten years from the date of grant and generally vest on a monthly basis over three The fair value of each employee and non-employee stock option grant under the 2019 Plan and 2023 Plan are estimated on the date of grant using the Black-Scholes option-pricing model. Due to the Company’s limited operating history and a lack of company-specific historical and implied volatility data, the Company estimated expected volatility based on the historical volatility of a group of similar companies that are publicly traded. The historical volatility data was computed using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. Due to the lack of historical exercise history, the expected term of the Company’s stock options for employees has been determined utilizing the “simplified” method for awards. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. The expected dividend yield is zero since the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. A summary of the Company’s stock option activity for the three months ended March 31, 2024 is as follows: Number of Stock Options Weighted Outstanding as of December 31, 2023 2,078,986 $ 6.25 Granted 2,295,000 1.62 Forfeited (109,725) 6.65 Exercised — — Outstanding as of March 31, 2024 4,264,261 $ 3.75 The weighted average assumptions used in the Black-Scholes option pricing model to determine the fair value of stock option grants for the three months ended March 31, 2024 were as follows: 2023 Plan Common stock fair value $ 1.62 Risk-free interest rate 4.2 % Expected volatility 92.0 % Expected term (in years) 6.9 Expected dividend yield — % Stock options outstanding, vested and expected to vest and exercisable as of March 31, 2024 are as follows: Number of Weighted Weighted- Total Outstanding as of December 31, 2023 2,078,986 8.86 $ 6.25 $ 317 Outstanding as of March 31, 2024 4,264,261 3.97 $ 3.75 $ 825 Vested and expected to vest as of March 31, 2024 4,264,261 3.97 $ 3.75 $ 825 Exercisable as of March 31, 2024 1,038,115 8.68 $ 4.31 $ 289 Intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that had exercise prices that were lower than the per share fair value of the common stock on the related measurement date. The aggregate fair value of stock options vested during the three months ended March 31, 2024 was $3.8 million . As of March 31, 2024 , the total unrecognized stock-based compensation related to unvested stock option awards granted was $12.4 million , which the Company expects to recognize over a remaining weighted- average period of approximately 3.1 years . Stock-based compensation expense, recognized in the Company’s unaudited condensed consolidated statements of operations and comprehensive loss for the 2019 Plan was recorded as follows (in thousands): Three Months Ended 2024 2023 Research and development $ 145 $ 330 General and administrative 972 928 Total stock-based compensation expense $ 1,117 $ 1,258

Property and Equipment, net

Property and Equipment, net	3 Months Ended
	Mar. 31, 2024
Property, Plant and Equipment [Abstract]
Property and Equipment, net	Property and Equipment, net Property and equipment, net consist of the following (in thousands): Useful Life March 31, December 31, Land — $ 5,025 $ 5,025 Buildings 40 years 8,325 8,325 Furniture and fixtures 7 years 749 749 Lab equipment 5 years 4,004 4,004 Leasehold improvements Lesser of estimated useful life or 52 52 Office equipment 5 years 17 17 Vehicles 5 years 27 112 18,199 18,284 Less: Accumulated depreciation (4,063) (3,825) $ 14,136 $ 14,459 Depreciation expense related to property and equipment was $0.3 million and $0.3 million for the three months ended March 31, 2024 and 2023 , respectively. Less than $0.1 million in losses and no gains or losses on the disposal of property and equipment have been recorded for the three months ended March 31, 2024 and 2023, respectively

Additional Balance Sheet Inform

Additional Balance Sheet Information	3 Months Ended
	Mar. 31, 2024
Balance Sheet Related Disclosures [Abstract]
Additional Balance Sheet Information	Additional Balance Sheet Information Prepaid expenses and other current assets consist of the following (in thousands): March 31, December 31, Prepaid expenses $ 1,250 $ 1,565 Other receivables 26 26 Revolving line of credit issuance fees 47 47 Other — 16 Prepaid expenses and other current assets $ 1,323 $ 1,654 Accounts payable and accrued expenses consist of the following (in thousands): March 31, December 31, Accounts payable $ 12,835 $ 11,040 Accrued liabilities 1,630 1,360 Employee compensation 733 911 Other 115 84 Accounts payable and accrued expenses $ 15,313 $ 13,395

Collaboration Agreement

Collaboration Agreement	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration Agreement	Collaboration Agreement On September 17, 2020, the Company entered into a strategic collaboration with Affimed GmbH (“ Affimed ”) to initiate a Phase 1/2 trial of SNK01 in combination with AFM24, a tetravalent biologic created by Affimed designed to direct NK cell killing of epidermal growth factor receptor (“ EGFR ”) expressing tumors. Under the collaboration agreement, the Company and Affimed split the development costs of the combination product equally. The study associated with the strategic collaboration with Affimed was discontinued by mutual agreement in June 2023. Total reductions to research and development expenses for the three months ended March 31, 2024 and 2023 were less than $0.1 million and $0.1 million respectively.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases In February 2018 , the Company entered into an operating lease agreement for office space located in 10 Pasteur, Irvine with a lease term of approximately five years . Rent payments commenced in February 2018. The lease expired on February 5, 2023. In October 2021 , the Company entered into an operating lease agreement for office space located in 19700 Fairchild with a lease term of approximately two years with an option to extend the term for one two -year term, which at the time was not reasonably assured of exercise and therefore, not included in the lease term. Rent payments commenced in December 2021 . The lease expired on December 31, 2023 . On November 9, 2023, the Company entered into a new operating lease agreement for office space located in Irvine, California with a lease term of approximately three years and rent payments commencing on January 1, 2024 . The lease commencement date is January 1, 2024. As of March 31, 2024, the Company recorded an aggregate ROU asset of $0.5 million with an accumulated amortization of less than $0.1 million in the unaudited condensed consolidated balance sheets as operating lease right of use assets, net, and an aggregate lease liability of $0.5 million in the balance sheet, which is comprised of $0.2 million operating lease liability, current and $0.3 million of operating lease liability, non-current. As of March 31, 2024, the weighted-average remaining lease term is 2.8 years and the weighted-average discount rate is 22.4%. Future minimum lease payments under the new office lease are as follows (in thousands): Minimum lease 2024 (excluding the three months ended 3/31/2024) $ 176 2025 242 2026 249 Total operating lease liability $ 667 License Agreements The Company has entered into exclusive license agreements with NKMAX, as amended in October 2021, April 2023 and August 2023 (“ Intercompany License ”), pursuant to which the Company acquired certain intellectual property for the development of treatments for cancer and other fields of use. Pursuant to each license agreement, as consideration for an exclusive license to the intellectual property, the Company paid an upfront fee of $1.0 million (“ Licensed Technology ”), which was recognized as research and development expense in the period paid as the license has no alternative future use. Additionally, the Company is also required to pay one-time milestone payments for the first receipt of regulatory approval by the Company or any of its affiliates for a Licensed Technology in the following jurisdictions (and amounts): the United States ( $5.0 million ), the European Union ( “EU” ) ( $4.0 million ), and four other countries ( $1.0 million each). The Company is obligated to pay a mid-single digit royalty on net sales of Licensed Technology by it, its affiliates or its sublicensees, subject to customary reductions. The Company is also required to pay a percentage of its sublicensing revenue ranging from a low double-digit percentage to a mid-single digit percentage. As of March 31, 2024 , the Company has not paid any milestone payments and no sales of Licensed Technology have occurred. Litigation The Company is subject to legal proceedings and claims, which arise in the ordinary course of business. The Company is not subject to any currently pending legal matters or claims that would have a material adverse effect on its financial position, results of operations or cash flows. In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnifications. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future but have not yet been made. The Company accrues a liability for such matters when it is probable that future expenditures will be made, and such expenditures can be reasonably estimated. No amounts were accrued as of March 31, 2024 and December 31, 2023 .

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2024
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Convertible 12% Promissory Notes On April 1, 2024 , the Company entered into a convertible 12% promissory note agreement with lender who is also an FPA Investor for $0.2 million with a one year term , issued at a 10.0% discount. The lender retains the option to convert any or all outstanding and unpaid principal amount and interest into shares of the Company's common stock from the date of issuance until the maturity date. Concurrently with this agreement, the Company issued the lender 166,667 shares of common stock as well as warrants that allow the lender to acquire up to 220,000 shares of common stock at an initial exercise price of $2.00 per share, subject to adjustment. On April 1, 2024 , the Company entered into a 12% promissory note agreement for $0.3 million with a one year term , issued at a 10.0% discount. The lender retains the option to convert any or all outstanding and unpaid principal amount and interest into shares of the Company's common stock from the date of issuance until the maturity date. Concurrently with this agreement, the Company issued the lender 250,000 shares of common stock as well as warrants that allow the lender to acquire up to 330,000 shares of common stock at an initial exercise price of $2.00 per share, subject to adjustment. On May 9, 2024, the promissory note was repaid in full for an aggregate payment of $0.4 million . On April 8, 2024, the Convertible 12% Promissory Note entered into on March 21, 2024 was repaid in full, for an aggregate payment of $ 0.4 million . On April 28, 2024 the Company entered into letter agreements with two holders of Convertible 12% Promissory Notes, who are also FPA Investors, which were originally entered into on March 26, 2024 and April 1, 2024. Pursuant to the Convertible 12% Promissory Notes, the holders of the notes may, in their sole discretion, require the Company to repay all or any portion of the outstanding principal amount and interest upon the receipt of cash proceeds in excess of $5.0 million. Pursuant to the letter agreements, the holders have agreed not to exercise the right to repayment until the cash proceeds received exceed an additional $5.0 million (for a total of $10.0 million in cash proceeds from the issuance date of each respective note). In exchange for signing the letter agreements, the Company has agreed to (i) pay cash consideration to each holder for an aggregate of $0.1 million, (ii) issue an aggregate of 416,667 shares of common stock to the holders, and (iii) issue an aggregate of 550,000 warrants entitling each holder to purchase shares of common stock at an exercise price of $2.00 per share. On April 30, 2024 the Company entered into a convertible 12% promissory note agreement for $0.2 million with a one year term, issued at a less than $0.1 million discount. The lender retains the option to convert any or all outstanding and unpaid principal amount and interest into shares of the Company's common stock from the date of issuance until the maturity date. Concurrently with this agreement, the Company issued the lender 125,000 shares of common stock as well as warrants that allow the lender to acquire up to 165,000 shares of common stock at an initial exercise price of $2.00 per share, subject to adjustment. On May 1, 2024, the Company entered into a convertible 12% promissory note agreement for $0.2 million with a one year term, issued at a 10.0% purchase discount. The lender retains the option to convert any or all outstanding and unpaid principal amount and interest into shares of the Company's common stock from the date of issuance until the maturity date. Concurrently with this agreement, the Company issued the lender 166,667 shares of common stock as well as warrants that allow the lender to acquire up to 220,000 shares of common stock at an initial exercise price of $2.00 per share, subject to adjustment. On May 1, 2024, the Company entered into a convertible 12% promissory note agreement for $0.1 million with a one year term, issued at a less than $0.1 million discount. The lender retains the option to convert any or all outstanding and unpaid principal amount and interest into shares of the Company's common stock from the date of issuance until the maturity date. Concurrently with this agreement, the Company issued the lender 101,461 shares of common stock as well as warrants that allow the lender to acquire up to 133,929 shares of common stock at an initial exercise price of $2.00 per share, subject to adjustment. On May 6, 2024, the Company entered into a convertible 12% promissory note agreement with a related party for $0.4 million with a one year term, issued at 10.0% discount. The lender retains the option to convert any or all outstanding and unpaid principal amount and interest into shares of the Company's common stock from the date of issuance until the maturity date. Concurrently with this agreement, the Company issued the lender 333,333 shares of common stock as well as warrants that allow the lender to acquire up to 440,000 shares of common stock at an initial exercise price of $2.00 per share, subject to adjustment. On May 9, 2024, the Convertible 12% Promissory Note entered into on March 26, 2024 was repaid in full, for an aggregate payment of $ 0.4 million . Convertible Secured Promissory Note On April 5, 2024, the Company entered into a convertible secured promissory note agreement for $5.0 million with an interest rate of the one month secured overnight financing rate plus 2.9% payable in cash in arrears on a monthly basis, with payments commencing one month from issuance which will mature on October 4, 2026. The convertible promissory note was issued in two tranches, the first of which was for $1.0 million and closed on April 8, 2024 and the second tranche was for $4.0 million which closed on April 9, 2024. The convertible secured promissory note is secured by a second lien on the Company’s owned real property located in Santa Ana, California. The convertible secured promissory note is subordinate to the $5.0 million revolving line of credit. The outstanding principal amount is convertible at any time until its maturity at the option of the lender into common stock at a $2.00 conversion price (subject to anti-dilution adjustments for stock splits and the like). Concurrently with this agreement, the lender is entitled to receive 833,333 shares of common stock upon the first closing and an amount of shares equal to $2.5 million divided by a five days VWAP measurement upon issuance in connection with the second closing. The lender is also entitled to warrants to acquire up to 1,000,000 shares of common stock at an initial exercise price of $2.00 per share, subject to adjustment. Forward Purchase Contract Amendment On April 11, 2024 , the Company amended their Forward Purchase Agreement with an FPA Investor, which had been previously amended on January 19, 2024 , to amend the Reset Price to establish a floor of $1.27 and gives the FPA Investor the ability to purchase up to 248,360 additional FPA Shares. Following this amendment, the FPA Investors may subscribe for and purchase a total of 1,416,350 additional shares of common stock under the Private Placement Agreements. Convertible Bridge Loans On April 12, 2024, the maturity of the 2024 Related Party Convertible Bridge Loan was amended to be the earliest of (i) 90 days from issuance, (ii) upon a financing event with third parties exceeding $5.0 million, (iii) the occurrence of any event of default, or (iv) the acceleration of the amended and restated short term bridge note. The 2024 Related Party Convertible Bridge Loan was repaid in full on April 17, 2024 for an aggregate payment of $0.5 million On April 18, 2024, two of the Convertible Bridge Loans entered into on February 7, 2024 and March 21, 2024 were repaid in full, for an aggregate payment of $0.3 million . On April 19, 2024 , one of the Convertible Bridge Loans was amended to extend the maturity date to be the earliest of (i) 90 days from issuance, (ii) upon a financing event with third parties exceeding $5.0 million, (iii) the occurrence of any event of default, or (iv) the acceleration of the amended and restated short term bridge note. In connection with the amendment, the repayment amount was amended to include a 24.6% bridge premium and the Company issued the lender 16,667 shares of common stock as well as warrants that allow the lender to acquire up to 22,000 shares of common stock at an initial exercise price of $2.00 per share. On April 25, 2024, $0.1 million , representing a portion of the outstanding balance was repaid to the lender. Less than $0.1 million remains outstanding on the related Convertible Bridge Loan. Zero Coupon Convertible Promissory Note On May 7, 2024, the Company entered into a zero coupon convertible promissory note agreement for $0.6 million with a one year term, issued at $0.1 million discount. The lender retains the option to convert any or all outstanding and unpaid principal amount and interest into shares of the Company's common stock from the date of issuance until the maturity date. Concurrently with this agreement, the Company issued the lender 416,667 shares of common stock as well as warrants that allow the lender to acquire up to 550,000 shares of common stock at an initial exercise price of $2.00 per share, subject to adjustment. Pursuant to the agreement, the Company may issue up to three additional zero coupon convertible promissory notes in the aggregate principal amount of $1.8 million . In connection with the three additional tranches, the Company may issue an aggregate of up to 1,250,000 additional shares of common stock and issue warrants that entitle holders to an aggregate of up to 1,650,000 shares of common stock at the lender’s sole discretion. Each additional promissory note will have identical terms as the original note, and each additional common stock purchase warrant will have identical terms as the original warrant. Convertible Promissory Notes On May 9, 2024, the Company entered into a convertible promissory note agreement for $0.4 million with a one year term, issued at $0.1 million discount. The lender retains the option to convert any or all outstanding and unpaid principal amount and interest into shares of the Company's common stock from the date of issuance until the maturity date. Concurrently with this agreement, the Company issued the lender 250,000 shares of common stock as well as warrants that allow the lender to acquire up to 330,000 shares of common stock at an initial exercise price of $2.00 per share, subject to adjustment. Pursuant to the agreement, the Company may issue up to three additional convertible promissory notes in the aggregate principal amount of $1.1 million . In connection with the three additional tranches, the Company may issue an aggregate of up to 750,000 additional shares of common stock and issue warrants that entitle holders to an aggregate of up to 990,000 shares of common stock at the lender’s sole discretion. Each additional promissory note will have identical terms as the original note, and each additional common stock purchase warrant will have identical terms as the original warrant.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation NKMAX held a majority of the voting power of Legacy NKGen before the Business Combination and continued to hold a majority of the voting power of the Company after the Business Combination. Therefore, as there was no change in control, the Business Combination was accounted for as a common control transaction with respect to Legacy NKGen along with a reverse recapitalization of the Company. Accordingly, for accounting purposes, the financial statements of the Company represent a continuation of the financial statements of Legacy NKGen with the Business Combination being treated as the equivalent of Legacy NKGen issuing shares for the net assets of Graf, accompanied by a recapitalization. The net assets of Graf were recognized as of the Closing at historical cost, with no goodwill or other intangible assets recorded. Operations prior to the Business Combination are presented as those of Legacy NKGen and the accumulated deficit of Legacy NKGen has been carried forward after Closing. Upon the consummation of the Business Combination, all of Legacy NKGen’s equity was converted into equity of the Company based upon an exchange ratio (“ Exchange Ratio ”). In addition, all stock options of Legacy NKGen were converted using the Exchange Ratio into options exercisable for shares of the Company with the same terms and vesting conditions. The Exchange Ratio as of September 29, 2023, the date of Closing, was approximately 0.408. All periods prior to the Business Combination have been retrospectively adjusted using the Exchange Ratio to reflect the reverse recapitalization. In connection with the reverse recapitalization treatment of the Business Combination, all issued and outstanding securities of Graf upon Closing were treated as issuances of the Company upon the consummation of the Business Combination. The accompanying financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (“ SEC ”) and generally accepted accounting principles in the United States of America (“ US GAAP ”). The Company maintains its accounting records under the accrual method of accounting in conformity with US GAAP. The condensed consolidated balance sheet as of December 31, 2023 included herein was derived from the audited financial statements as of that date. Certain information and disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such regulations. Accordingly, these unaudited condensed consolidated financial statements and accompanying footnotes should be read in conjunction with NKGen’s financial statements as of and for the year ended December 31, 2023 . The results for the interim periods are not necessarily indicative of results for the full year. In the opinion of management, all adjustments, of a normal recurring nature, considered necessary for a fair presentation have been included in the unaudited condensed consolidated financial statements. The Company believes that the disclosures provided herein are adequate to prevent the information presented from being misleading.
Principles of Consolidation	Principles of Consolidation
Use of Estimates	Use of Estimates The preparation of unaudited condensed consolidated financial statements in accordance with US GAAP requires management to make estimates and assumptions that impact the reported amounts of certain assets and liabilities, certain disclosures at the date of the unaudited condensed consolidated financial statements, as well as the reported amounts of revenues and expenses during the reporting period. The most significant estimates in the Company’s unaudited condensed consolidated financial statements include, but are not limited to, accrued clinical and research and development expenses, legacy convertible notes, convertible 12% promissory notes, senior convertible promissory notes due to related parties, forward purchase derivative liabilities, derivative warrant liabilities, derivative warrant assets, common stock, and equity awards. These estimates and assumptions are based upon historical experience, knowledge of current events, and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results could differ materially from those estimates.
Restricted Cash	Restricted Cash Restricted cash consists of funds that are contractually restricted due to a revolving line of credit, which was entered into during June 2023 . In accordance with the terms of the revolving line of credit, the Company was required to maintain $15.0 million in cash balances with the lender from March 31, 2024 until repayment of all principals and other payables to the lender under the revolving line of credit was made as additional collateral for the borrowings. In April 2024, the lender subsequently waived the minimum cash deposit requirement in exchange for the Company's agreement to use the lender as their primary banking relationship. As of both March 31, 2024 and December 31, 2023 , $0.3 million in restricted cash was recorded on the unaudited condensed consolidated balance sheet. The Company includes its restricted bank deposits in cash, cash equivalents and restricted cash when reconciling beginning-of-period and end-of-period total amounts shown on the unaudited condensed consolidated statements of cash flows for the three months ended March 31, 2024 .
Deferred Debt Issuance Costs / Debt	Deferred Debt Issuance Costs Debt For convertible debt instruments that are not considered liabilities under ASC 480 or ASC 815, the Company applies ASC 470, Debt , for the accounting of such instruments, including any premiums or discounts. The Company’s bridge loans, senior convertible promissory notes, and convertible bridge loans accounted for under ASC 470. Accrued interest paid-in-kind is added to the carrying amount of the Company’s senior convertible promissory notes.
Hybrid Instruments	Hybrid Instruments The Company follows Financial Accounting Standards Board (“ FASB ”) Accounting Standard Codification (“ ASC ”) 480, Distinguishing Liabilities from Equity
Derivative Instruments	Derivative Instruments FASB ASC 815, Derivatives and Hedging Activities
Subscription and Shareholder Receivables	Subscription and Shareholder Receivables The Company records stock issuances at the effective date. If the amounts are not funded upon issuance, the Company records a subscription receivable or shareholder receivable as an asset on the balance sheet. When subscription receivables or shareholder receivables are not received prior to the balance sheet date in satisfaction of the requirements under ASC 505, Equity , the subscription or shareholder receivable is reclassified as a contra account to stockholder’s equity (deficit) on the balance sheet.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate the carrying amount of an asset, or asset group, may not be recoverable. Recoverability is measured by a comparison of the carrying amount of an asset or asset group to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset or asset group exceeds its estimated future cash flows, an impairment charge is recognized by the amount by which the carrying amount of the asset or asset group exceeds the fair value of the asset or asset group. The Company has not recognized any impairment losses for the three months ended March 31, 2024 and 2023 .
Fair Value Option	Fair Value Option In lieu of bifurcation, on an instrument-by-instrument basis, the Company may elect the fair value option for certain financial instruments that meet the required criteria under ASC 825, Financial Instruments . The Company elected the fair value option for both its legacy convertible notes and convertible 12% promissory notes, which met the required criteria under ASC 825, Financial Instruments . Interest expense associated with both the legacy convertible and convertible 12% promissory notes is included in the change in fair value of such instruments.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company accounts for the fair value of its financial instruments under the framework established by US GAAP which defines fair value and expands disclosures about fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The standard describes a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value. These estimates may be subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. Level 1 — Quoted prices in active markets for identical assets or liabilities the Company has the ability to access at the measurement date. Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of assets or liabilities. Level 3 — Pricing inputs that are unobservable, supported by little or no market activity and are significant to the fair value of the assets or liabilities. Transfers to/from Levels 1, 2, and 3 are recognized at the beginning of the reporting period. There were no transfers to/from Levels 1, 2, and 3 during three months ended March 31, 2024 and 2023 . ASC 820, Fair Value Measurement, states that in many cases, the transaction price will equal the fair value (for example, that might be the case when on the transaction date, the transaction to buy an asset takes place in the market in which the asset is sold). In determining whether a transaction price represents the fair value at initial recognition, the Company considers various factors such as whether the transaction was between related parties, is a forced transaction, or whether the unit of account for the transaction price does not represent the unit of account for the measured instrument. The Company does not measure assets at fair value on a recurring basis. The Company's liabilities that are measured at fair value on a recurring basis are its liability classified warrants, convertible 12% promissory notes, and forward purchase derivative liabilities. Refer to Note 9, Fair Value of Financial Instruments , for further discussion regarding the Company’s fair value measurements. The carrying value of the Company’s related party loans approximates fair value as the stated interest rate approximates market rates for similar loans and due to the short-term nature of such loans, which are due within three years or less from issuance. The carrying value of the Company’s cash, restricted cash, accounts payable, accrued expenses, bridge loans, convertible bridge loans, other current liabilities, and revolving line of credit approximates fair value primarily due to the short-term nature of such accounts.
Leases	Leases The Company accounts for its leases under ASC 842, Leases . The operating lease right-of-use (“ ROU ”) asset represents the Company’s right to use an underlying asset during the lease term, and operating lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating leases are included in the ROU asset, current operating lease liabilities, and non-current operating lease liabilities in the accompanying condensed consolidated balance sheets. The operating lease ROU asset and lease liabilities are initially recognized based on the present value of the future minimum lease payments over the lease term at commencement date calculated using the Company’s incremental borrowing rate applicable to the lease asset, unless the implicit rate is readily determinable. The operating lease ROU asset also includes any lease payments made at or before lease commencement and exclude any lease incentives received. The Company determines the lease term as the noncancelable period of the lease and may include options to extend or terminate the lease when it is reasonably certain the Company will exercise that option. Leases with a term of 12 months or less are not recognized in the balance sheet. The Company’s leases do not contain any residual value guarantees. Lease expense for minimum lease payments is recognized as rent expense on a straight-line basis over the lease term. Operating expenses such as common area maintenance and utilities are treated as variable lease payments.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense is comprised of stock options awarded to employees and consultants. The Company accounts for share-based awards under the fair value method prescribed by ASC 718-10, Stock Compensation . The fair value of stock options is estimated using the Black-Scholes option pricing model on the date of grant. This option pricing model involves a number of estimates, including the per share value of the underlying common stock, exercise price, estimate of future volatility, expected term of the stock option award, risk-free interest rate and expected annual dividend yield. The fair value of the shares of common stock underlying the stock options has historically been determined by the Company’s board of directors as there was no public market for the underlying common stock prior to October 2, 2023. The Company’s board of directors determines the fair value of the Company’s common stock by considering a number of objective and subjective factors including contemporaneous third-party valuations of its common stock, the valuation of comparable companies, sales of the Company’s common stock to outside investors in arms-length transactions, the Company’s operating and financial performance, the lack of marketability, and general and industry specific economic outlook, and the implied fair values upon a merger transaction, amongst other factors. The Company recognizes the expense for options with graded-vesting schedules on a straight-line basis over the requisite service period, which is generally the vesting period. Forfeitures are recognized as they occur.
Basic and Diluted Net Loss Per Common Share	Basic and Diluted Net Loss Per Common Share Basic net loss per common share is computed by dividing net loss for the year by the weighted-average number of common shares outstanding during the year. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding and potentially dilutive securities outstanding for the period using the treasury stock or if-converted method if their inclusion is dilutive. Diluted net loss per common share is the same as basic net loss per common share because the inclusion of potentially dilutive shares would be anti-dilutive to the calculation of net loss per common share. The Company has one class of shares issued and outstanding. Accordingly, basic and diluted net loss per share is not allocated among multiple classes of shares. Basic and diluted net loss per share for all periods prior to the Closing have been retrospectively adjusted by the Exchange Ratio to affect the reverse recapitalization. Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share for three months ended March 31, 2024 include the following: Private warrants 4,721,533 Working capital warrants 523,140 Public warrants 3,432,286 PIPE warrants 10,209,994 Stock options 1,969,261 SPA warrants 1,000,000 Senior convertible notes’ shares 1,000,000 Deferred founder shares (1) 1,173,631 Convertible bridge loan warrants 1,250,000 Convertible bridge loan consideration shares 7,334 Convertible bridge loans 619,146 Convertible 12% promissory note warrants 660,000 Convertible 12% promissory notes 367,850 Total 26,934,175 (1) As described in Note 8, Related Party Transactions , deferred founder shares do not have voting rights, do not participate in dividends and are not transferrable absent the Company’s consent. Therefore, while deferred founder shares are considered outstanding for legal purposes and are included in the total quantity of outstanding shares on the unaudited condensed consolidated statements of stockholders’ deficit, they are not considered outstanding for accounting purposes, including basic and diluted net loss per share purposes.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In December 2023 , the FASB issued ASU No. 2023-09, Improvements to Income Tax Disclosures (Topic 740) . The ASU requires disaggregated information about a reporting entity’s effective tax rate reconciliation as well as additional information on income taxes paid. The ASU is effective on a prospective basis for annual periods beginning after December 15, 2024. Early adoption is also permitted for annual financial statements that have not yet been issued or made available for issuance. This ASU will result in the required additional disclosures being included in the Company's unaudited condensed consolidated financial statements, once adopted. The Company is currently evaluating the impact of this standard on its financial statements and related disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Schedule of Potentially Antidilutive Shares Excluded from Computation of Diluted Net Loss Per Share	Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share for three months ended March 31, 2024 include the following: Private warrants 4,721,533 Working capital warrants 523,140 Public warrants 3,432,286 PIPE warrants 10,209,994 Stock options 1,969,261 SPA warrants 1,000,000 Senior convertible notes’ shares 1,000,000 Deferred founder shares (1) 1,173,631 Convertible bridge loan warrants 1,250,000 Convertible bridge loan consideration shares 7,334 Convertible bridge loans 619,146 Convertible 12% promissory note warrants 660,000 Convertible 12% promissory notes 367,850 Total 26,934,175 (1) As described in Note 8, Related Party Transactions , deferred founder shares do not have voting rights, do not participate in dividends and are not transferrable absent the Company’s consent. Therefore, while deferred founder shares are considered outstanding for legal purposes and are included in the total quantity of outstanding shares on the unaudited condensed consolidated statements of stockholders’ deficit, they are not considered outstanding for accounting purposes, including basic and diluted net loss per share purposes.

Reverse Recapitalization (Table

Reverse Recapitalization (Tables)	3 Months Ended
	Mar. 31, 2024
Reverse Recapitalization [Abstract]
Schedule of Reverse Recapitalization	The following tables reconcile elements of the Business Combination to the Company’s unaudited condensed consolidated financial statements, and should be read in conjunction with the footnotes referenced above (in thousands, except share amounts): Shares Graf public shares, net of redemptions 93,962 Private placement investors’ shares 3,683,010 Graf founder shares 2,516,744 Total Graf shares outstanding immediately prior to the Business Combination 6,293,716 Conversion of Legacy NKGen convertible promissory notes (after the application of the Exchange Ratio) 2,278,598 Legacy NKGen rollover shares (after the application of the Exchange Ratio) 13,316,662 Total Legacy NKGen shares 15,595,260 Total Company common stock outstanding immediately following the Business Combination 21,888,976 (In thousands) Recapitalization Closing proceeds Proceeds from issuance of common stock $ 1,667 Proceeds from issuance of PIPE warrants 10,210 Proceeds from issuance of senior convertible promissory notes with warrants 10,000 Closing disbursements Less: Payment of Graf deferred underwriter fees (1,250) Less: Payment of Graf transaction costs at Closing (1) (7,456) Less: Payment of Legacy NKGen transaction costs at Closing (3,510) Net cash proceeds from the Business Combination at Closing $ 9,661 Less: Payment of Legacy NKGen transaction costs prior to Closing (2,089) Net cash proceeds from the Business Combination $ 7,572 Noncash activity Conversion of legacy NKGen convertible promissory notes 18,913 Less: Operating liabilities assumed from Graf (860) Less: Unpaid transaction costs – assumed from Graf (1) (5,400) Less: Unpaid transaction costs – Legacy NKGen (1,938) Liability-classified instruments Less: Fair value of PIPE warrants (10,210) Less: Fair value of forward purchase derivative liabilities (20,201) Less: Fair value of senior convertible promissory notes (2) (9,707) Less: Fair value of private warrants (1,841) Less: Fair value of working capital warrants (204) Net equity impact of the Business Combination $ (23,876) (1) The Graf transaction costs includes a $4.0 million accrual related to a certain vendor to be paid in cash and common stock of $2.0 million each. At Closing, a cash payment of $1.3 million was disbursed to this vendor. The remaining $2.7 million amount was recognized as a component of the unpaid transaction costs assumed from Graf, of which $0.7 million represents a cash settlement obligation, and the remaining $2.0 million represents an obligation to issue a variable number of shares for a fixed monetary amount which was accounted for as a liability under ASC 480, Distinguishing Liabilities from Equity (“ ASC 480 ”). Under ASC 480, the obligation to issue shares is not subsequently measured at fair value with changes recorded in earnings because the monetary amount is fixed. (2) Represents allocated fair value.

Private Placement (Tables)

Private Placement (Tables)	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments	Upon execution of the FPA Amendment in December 2023, the Company recognized a loss on amendment to forward purchase contract as set forth below (in thousands): Loss on Amendment Reduction of subscription receivable $ 15,123 Change in fair value in connection with the amendment of forward purchase contracts (14,181) Cash received in connection with the amendments (500) Loss on amendment to forward purchase contracts $ 442 Upon execution of the 2024 FPA Amendments, the Company recognized a loss on amendment to forward purchase contract as set forth below (in thousands): Loss on Amendment Reduction of subscription receivable $ 2,764 Reduction in forward purchase derivative liabilities (1,418) Cash received in connection with the amendments (950) Loss on amendment to forward purchase contracts $ 396 The following presents a reconciliation of the subscription receivable and forward purchase derivative liabilities during the three months ended March 31, 2024 (in thousands): Subscription Receivables Forward Purchase Derivative Liabilities Balance at December 31, 2023 $ 17,792 $ 15,804 Amendment of forward purchase contracts (2,764) (1,418) Change in fair value of forward purchase derivative liabilities — (535) Sales and settlement of forward purchase contracts (4,639) (3,766) Ending balance at March 31, 2024 $ 10,389 $ 10,085 Derivatives and Hedging . All other terms and conditions remained unchanged. PIPE Warrant Amendment Cash proceeds $ 250 Reduction in PIPE Warrant derivative liability 429 Gain on amendment of PIPE warrant agreement $ 679
Schedule of Sales of FPA Shares and Proceeds to the Company	The following table summarizes the sales of FPA Shares and proceeds to the Company as of March 31, 2024 (in thousands): Sales of FPA Shares Total sales of FPA Shares $ 2,626 Shortfall Sales (1,753) Proceeds received from sales of FPA Shares $ 873

Warrants (Tables)

Warrants (Tables)	3 Months Ended
	Mar. 31, 2024
Warrants [Abstract]
Schedule of Derivative Instruments	Upon execution of the FPA Amendment in December 2023, the Company recognized a loss on amendment to forward purchase contract as set forth below (in thousands): Loss on Amendment Reduction of subscription receivable $ 15,123 Change in fair value in connection with the amendment of forward purchase contracts (14,181) Cash received in connection with the amendments (500) Loss on amendment to forward purchase contracts $ 442 Upon execution of the 2024 FPA Amendments, the Company recognized a loss on amendment to forward purchase contract as set forth below (in thousands): Loss on Amendment Reduction of subscription receivable $ 2,764 Reduction in forward purchase derivative liabilities (1,418) Cash received in connection with the amendments (950) Loss on amendment to forward purchase contracts $ 396 The following presents a reconciliation of the subscription receivable and forward purchase derivative liabilities during the three months ended March 31, 2024 (in thousands): Subscription Receivables Forward Purchase Derivative Liabilities Balance at December 31, 2023 $ 17,792 $ 15,804 Amendment of forward purchase contracts (2,764) (1,418) Change in fair value of forward purchase derivative liabilities — (535) Sales and settlement of forward purchase contracts (4,639) (3,766) Ending balance at March 31, 2024 $ 10,389 $ 10,085 Derivatives and Hedging . All other terms and conditions remained unchanged. PIPE Warrant Amendment Cash proceeds $ 250 Reduction in PIPE Warrant derivative liability 429 Gain on amendment of PIPE warrant agreement $ 679

Convertible Notes (Tables)

Convertible Notes (Tables)	3 Months Ended
	Mar. 31, 2024
Debt Disclosure [Abstract]
Convertible Debt	The following table presents a reconciliation of the Senior Convertible Notes (in thousands): Senior Convertible Balance as of December 31, 2023 $ 9,930 Amortization of discount 11 Paid-in-kind interest 206 Balance as of March 31, 2024 $ 10,147

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of Fair Value Hierarchy	Liabilities measured at fair value on a recurring basis as of March 31, 2024 are as follows (in thousands):  Fair Value Measurements at Reporting Date Using Balance as of Level 1 Level 2 Level 3 Convertible 12% Promissory Notes $ 728 $ — $ — $ 728 Private Warrants 803 — — 803 Working Capital Warrants 89 — — 89 PIPE Warrants 19,704 — — 19,704 Convertible Bridge Loan Warrants 1,822 — — 1,822 Convertible 12% Promissory Note Warrants 942 — — 942 Forward Purchase Derivative Liabilities 10,085 — — 10,085 Consideration Shares 14 14 — — Total $ 34,187 $ 14 $ — $ 34,173
Reconciliation of Convertible 12% Promissory Notes	The following table presents a reconciliation of the Convertible 12% Promissory Notes (in thousands): Convertible 12% Promissory Notes Balance as of December 31, 2023 $ — Issuance 250 Change in fair value $ 478 Balance as of March 31, 2024 $ 728
Fair Value Unobservable Assumption Inputs	The following unobservable assumptions were used in determining the fair value of the Convertible 12% Promissory Notes at March 31, 2024: Credit spread 27.5 % Equity volatility 45.0 % The following unobservable assumptions were used in determining the fair value of the liability classified warrants at March 31, 2024 and December 31, 2023: At March 31, 2024 At December 31, 2023 or closing date if later Private Warrants and Working Capital Warrants Private Warrants’ volatility 55.5 % 35.3 % Dividend yield (per share) — — Convertible Bridge Loan Warrants Volatility 100.0 % 105.0 % Dividend yield (per share) — — Convertible 12% Promissory Note Warrants Equity volatility 100.0 % — PIPE Warrants Credit spread 19.0 % 12.7 % Equity volatility 105.0 % 100.0 % The following unobservable assumptions were used in determining the fair value of the PIPE Warrants immediately before and after modification at February 9, 2024: Credit spread 17.8 % Equity volatility 105.0 % The following unobservable assumptions were used in determining the fair value of the forward purchase derivative liabilities at the respective balance sheet and amendment dates: March 31, 2024 February 21, 2024 January 19, 2024 December 31, 2023 Dividend yield 0.0 % 0.0 % 0.0 % 0.0 % Equity volatility 120.0 % 145.0 % 105.0 % 115.0 %
Schedule of Derivative Liabilities	The following table represent a reconciliation of all liability classified warrants (in thousands): Private Warrants Working Capital Warrants Convertible Bridge Loan Warrants Convertible 12% Promissory Note Warrants PIPE Warrants Total Balance December 31, 2023 $ 377 $ 42 $ — $ — $ 25,339 $ 25,758 Issuances — — 1,424 323 — 1,747 Change in fair value in connection with PIPE Warrants Amendment — — — — (429) (429) Change in fair value 426 47 398 619 (5,206) (3,716) Balance as of March 31, 2024 $803 $89 $1,822 $942 $ 19,704 $ 23,360

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Schedule of Stock Option Activity	A summary of the Company’s stock option activity for the three months ended March 31, 2024 is as follows: Number of Stock Options Weighted Outstanding as of December 31, 2023 2,078,986 $ 6.25 Granted 2,295,000 1.62 Forfeited (109,725) 6.65 Exercised — — Outstanding as of March 31, 2024 4,264,261 $ 3.75 Stock options outstanding, vested and expected to vest and exercisable as of March 31, 2024 are as follows: Number of Weighted Weighted- Total Outstanding as of December 31, 2023 2,078,986 8.86 $ 6.25 $ 317 Outstanding as of March 31, 2024 4,264,261 3.97 $ 3.75 $ 825 Vested and expected to vest as of March 31, 2024 4,264,261 3.97 $ 3.75 $ 825 Exercisable as of March 31, 2024 1,038,115 8.68 $ 4.31 $ 289
Schedule of Stock Option Valuation Assumptions	The weighted average assumptions used in the Black-Scholes option pricing model to determine the fair value of stock option grants for the three months ended March 31, 2024 were as follows: 2023 Plan Common stock fair value $ 1.62 Risk-free interest rate 4.2 % Expected volatility 92.0 % Expected term (in years) 6.9 Expected dividend yield — %
Schedule of Stock-Based Compensation Expense	Stock-based compensation expense, recognized in the Company’s unaudited condensed consolidated statements of operations and comprehensive loss for the 2019 Plan was recorded as follows (in thousands): Three Months Ended 2024 2023 Research and development $ 145 $ 330 General and administrative 972 928 Total stock-based compensation expense $ 1,117 $ 1,258

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	3 Months Ended
	Mar. 31, 2024
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment, net consist of the following (in thousands): Useful Life March 31, December 31, Land — $ 5,025 $ 5,025 Buildings 40 years 8,325 8,325 Furniture and fixtures 7 years 749 749 Lab equipment 5 years 4,004 4,004 Leasehold improvements Lesser of estimated useful life or 52 52 Office equipment 5 years 17 17 Vehicles 5 years 27 112 18,199 18,284 Less: Accumulated depreciation (4,063) (3,825) $ 14,136 $ 14,459

Additional Balance Sheet Info_2

Additional Balance Sheet Information (Tables)	3 Months Ended
	Mar. 31, 2024
Balance Sheet Related Disclosures [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following (in thousands): March 31, December 31, Prepaid expenses $ 1,250 $ 1,565 Other receivables 26 26 Revolving line of credit issuance fees 47 47 Other — 16 Prepaid expenses and other current assets $ 1,323 $ 1,654
Schedule of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consist of the following (in thousands): March 31, December 31, Accounts payable $ 12,835 $ 11,040 Accrued liabilities 1,630 1,360 Employee compensation 733 911 Other 115 84 Accounts payable and accrued expenses $ 15,313 $ 13,395

Commitment and Contingencies (T

Commitment and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Lease Payments Under the New Office Lease	Future minimum lease payments under the new office lease are as follows (in thousands): Minimum lease 2024 (excluding the three months ended 3/31/2024) $ 176 2025 242 2026 249 Total operating lease liability $ 667

Company Information (Details)

Company Information (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Accumulated deficit	$ 167,512	$ 162,130
Cash and cash equivalents	$ 34	$ 26
Interest rate	12%
Convertible 12% promissory notes
Debt Instrument [Line Items]
Interest rate	12%
Convertible 12% promissory notes | Convertible Debt
Debt Instrument [Line Items]
Interest rate	12%

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) stock shares	Mar. 26, 2024	Dec. 31, 2023 USD ($)	Sep. 29, 2023	Jun. 30, 2023 USD ($)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Recapitalization exchange ratio				0.408
Interest rate	12%
Deferred debt issuance costs	$ 100		$ 100
Line of credit, minimum required cash balance					$ 15,000
Restricted cash	250		$ 250
Proceeds from shareholder receivables	$ 500
Number of class of shares | stock	1
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share | shares	26,934,175
Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Borrowing term	3 years
Convertible 12% promissory notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Interest rate	12%
Convertible 12% promissory notes | Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Interest rate	12%	12%
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share | shares	1,969,261

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details)	3 Months Ended
	Mar. 31, 2024 shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	26,934,175
Interest rate	12%
Convertible 12% promissory notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Interest rate	12%
Convertible 12% promissory notes | Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Interest rate	12%
Convertible 12% promissory note warrants | Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Interest rate	12%
Private warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	4,721,533
Working capital warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	523,140
Public warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	3,432,286
PIPE warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	10,209,994
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	1,969,261
SPA warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	1,000,000
Senior convertible notes’ shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	1,000,000
Deferred founder shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	1,173,631
Convertible bridge loan warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	1,250,000
Convertible bridge loan consideration shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	7,334
Convertible bridge loans
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	619,146
Convertible 12% promissory note warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	660,000
Convertible 12% promissory notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially anti-dilutive shares excluded from the calculation of diluted net loss per share	367,850

Reverse Recapitalization - Narr

Reverse Recapitalization - Narrative (Details) - USD ($) $ in Millions	Sep. 29, 2023	Sep. 28, 2023	Mar. 31, 2024	Dec. 31, 2023
Schedule Of Reverse Recapitalization [Line Items]
Converted shares (in shares)		5,579,266
Stock converted, reverse recapitalization (in shares)	2,278,598
Common stock outstanding (in shares)	21,888,976		22,388,976	21,888,976
Common stock, shares issued (in shares)			22,388,976	21,888,976
Stock options cancelled and converted (in shares)	2,101,760
Reverse recapitalization, transaction costs	$ 7.5
Legacy NKGen
Schedule Of Reverse Recapitalization [Line Items]
Common stock outstanding (in shares)	38,185,814
Common stock, shares issued (in shares)	38,185,814
Options, issued and outstanding (in shares)	5,146,354
Equity Instruments
Schedule Of Reverse Recapitalization [Line Items]
Reverse recapitalization, transaction costs	$ 4.2
Liability Instruments
Schedule Of Reverse Recapitalization [Line Items]
Reverse recapitalization, transaction costs	$ 3.3
Common Stock, Including Convertible Debt Stock
Schedule Of Reverse Recapitalization [Line Items]
Stock converted, reverse recapitalization (in shares)	15,595,262

Reverse Recapitalization - Sche

Reverse Recapitalization - Schedule of Reverse Recapitalization- Share Impact (Details)	Sep. 29, 2023 shares
Schedule Of Reverse Recapitalization [Line Items]
Total Legacy NKGen shares (in shares)	2,278,598
Legacy NKGen rollover shares (in shares)	13,316,662
Total Company common stock outstanding immediately following the Business Combination (in shares)	21,888,976
Graf public shares, net of redemptions | Graf Acquisition Partners IV LLC
Schedule Of Reverse Recapitalization [Line Items]
Total Graf shares outstanding immediately prior to the Business Combination (in shares)	93,962
Private placement investors’ shares | Graf Acquisition Partners IV LLC
Schedule Of Reverse Recapitalization [Line Items]
Total Graf shares outstanding immediately prior to the Business Combination (in shares)	3,683,010
Graf founder shares | Graf Acquisition Partners IV LLC
Schedule Of Reverse Recapitalization [Line Items]
Total Graf shares outstanding immediately prior to the Business Combination (in shares)	2,516,744
Common Shareholders | Graf Acquisition Partners IV LLC
Schedule Of Reverse Recapitalization [Line Items]
Total Graf shares outstanding immediately prior to the Business Combination (in shares)	6,293,716
Legacy NKGen
Schedule Of Reverse Recapitalization [Line Items]
Total Legacy NKGen shares (in shares)	15,595,260

Reverse Recapitalization - Sc_2

Reverse Recapitalization - Schedule of Reverse Recapitalization- Reconciliation Elements of The Business Combination to the Company’s Unaudited Condensed Consolidated Financial Statements (Details) - USD ($) $ in Thousands		3 Months Ended
	Sep. 29, 2023	Mar. 31, 2024	Mar. 31, 2023
Schedule Of Reverse Recapitalization [Line Items]
Proceeds from issuance of common stock	$ 1,667
Proceeds from amendment to the PIPE warrants	10,210	$ 250	$ 0
Proceeds from issuance of senior convertible promissory notes with warrants	10,000
Less: Payment of Graf deferred underwriter fees	(1,250)
Less: Payment of transaction costs at Closing		$ (40)	$ 0
Net cash proceeds from the Business Combination at Closing	9,661
Less: Payment of Legacy NKGen transaction costs prior to Closing	(2,089)
Net cash proceeds from the Business Combination	7,572
Conversion of legacy NKGen convertible promissory notes	18,913
Less: Operating liabilities assumed from Graf	(860)
Less: Fair value of PIPE warrants	(10,210)
Less: Fair value of forward purchase derivative liabilities	(20,201)
Less: Fair value of senior convertible promissory notes	(9,707)
Less: Fair value of private warrants	(1,841)
Less: Fair value of working capital warrants	(204)
Net equity impact of the Business Combination	(23,876)
Reverse recapitalization obligation, cash settlement	700
Reverse recapitalization obligation, shares issuable	2,000
Graf Acquisition Partners IV LLC
Schedule Of Reverse Recapitalization [Line Items]
Less: Payment of transaction costs at Closing	(7,456)
Less: Unpaid transaction costs	(5,400)
Legacy NKGen
Schedule Of Reverse Recapitalization [Line Items]
Less: Payment of transaction costs at Closing	(3,510)
Less: Unpaid transaction costs	(1,938)
Vendor
Schedule Of Reverse Recapitalization [Line Items]
Less: Payment of transaction costs at Closing	(1,300)
Less: Unpaid transaction costs	(2,700)
Vendor | Graf Acquisition Partners IV LLC
Schedule Of Reverse Recapitalization [Line Items]
Less: Unpaid transaction costs	(4,000)
Vendor | Graf Acquisition Partners IV LLC | Common Stock
Schedule Of Reverse Recapitalization [Line Items]
Less: Unpaid transaction costs	(2,000)
Vendor | Graf Acquisition Partners IV LLC | Cash
Schedule Of Reverse Recapitalization [Line Items]
Less: Unpaid transaction costs	$ (2,000)

Private Placement - Additional

Private Placement - Additional Information (Details)						2 Months Ended	3 Months Ended
	Sep. 29, 2024 USD ($) $ / shares shares	Mar. 31, 2024 USD ($) shares	Dec. 26, 2023 USD ($) d $ / shares shares	Sep. 29, 2023 USD ($)	Sep. 28, 2023 USD ($) shares	Feb. 29, 2024 USD ($) $ / shares shares	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 25, 2023 USD ($)
Derivative [Line Items]
Shares purchased (in shares) | shares					3,168,121
Repayment amount				$ 32,900,000	$ 32,900,000
Anniversary of closing period					1 year
Minimum escrow releasement					$ 0
Loss on amendment of forward purchase contracts				24,500,000
Forward purchase derivative liabilities		$ 10,085,000		20,200,000			$ 10,085,000		$ 15,804,000
Bonus stock				$ 4,300,000
Anniversary term				1 year
Loss on amendment of forward purchase contracts							396,000	$ 0
Change in fair value in connection with the amendment of forward purchase contracts			$ (14,200,000)
Proceeds from sale of FPA shares							$ 1,823,000	$ 0
Forecast
Derivative [Line Items]
Approaches or exceeds, threshold trigger (in USD per share) | $ / shares	$ 10.44
Decreases below, threshold trigger (in USD per share) | $ / shares	10.44
Change in share price | $ / shares	$ 2
Shortfall, consideration received on transaction	$ 100,000
Bonus Shares | Forecast
Derivative [Line Items]
Shares purchased (in shares) | shares	514,889
December 2023 FPA Amendment
Derivative [Line Items]
Repayment amount			$ 500,000
Number of additional shares available (in shares) | shares			200,000
Approaches or exceeds, threshold trigger (in USD per share) | $ / shares			$ 10.44
Number of shares re-designated (in shares) | shares			200,000
Sale of stock, common stock purchase agreement, prepayment shortfall increase available			$ 500,000
Pre-existing prepayment shortfall										$ 100,000
Loss on amendment of forward purchase contracts			$ 442,000
Discount of VWAP measurement			0.100
Derivative liability, additional share issuance of VWAP			0.900
VWAP trading days | d			20
Reduction of subscription receivable			$ 15,123,000
Change in fair value in connection with the amendment of forward purchase contracts			$ 14,181,000
2024 FPA Amendments
Derivative [Line Items]
Repayment amount						$ 1,000,000
Number of additional shares available (in shares) | shares			200,000			200,000
Decreases below, threshold trigger (in USD per share) | $ / shares						$ 10.44
Sale of stock, common stock purchase agreement, prepayment shortfall increase available						$ 1,100,000
Pre-existing prepayment shortfall						$ 700,000
Loss on amendment of forward purchase contracts			$ 396,000
Discount of VWAP measurement						0.100
Reduction of subscription receivable			2,764,000
Change in fair value in connection with the amendment of forward purchase contracts			$ 1,418,000
2024 FPA Amendments | FPA Investor
Derivative [Line Items]
Shares purchased (in shares) | shares		1,768,121

Private Placement - Forward Pur

Private Placement - Forward Purchase Contract (Details) - USD ($) $ in Thousands		3 Months Ended
	Dec. 26, 2023	Mar. 31, 2024	Mar. 31, 2023
Derivative [Line Items]
Reduction in forward purchase derivative liabilities	$ 14,200
Cash received in connection with the amendments		$ (500)	$ 0
Loss on amendment of forward purchase contracts		$ 396	$ 0
December 2023 FPA Amendment
Derivative [Line Items]
Reduction of subscription receivable	15,123
Reduction in forward purchase derivative liabilities	(14,181)
Cash received in connection with the amendments	(500)
Loss on amendment of forward purchase contracts	442
2024 FPA Amendments
Derivative [Line Items]
Reduction of subscription receivable	2,764
Reduction in forward purchase derivative liabilities	(1,418)
Cash received in connection with the amendments	(950)
Loss on amendment of forward purchase contracts	$ 396

Private Placement - Schedule of

Private Placement - Schedule of Sales of FPA Shares and Proceeds to the Company (Details) - USD ($) $ in Thousands			3 Months Ended
	Sep. 29, 2023	Sep. 28, 2023	Mar. 31, 2024
Subsidiary, Sale of Stock [Line Items]
Proceeds received from sales of FPA Shares	$ 32,900	$ 32,900
Total sales of FPA Shares
Subsidiary, Sale of Stock [Line Items]
Proceeds received from sales of FPA Shares			$ 2,626
Shortfall Sales
Subsidiary, Sale of Stock [Line Items]
Shortfall Sales			(1,753)
Proceeds received from sales of FPA Shares
Subsidiary, Sale of Stock [Line Items]
Proceeds received from sales of FPA Shares			$ 873

Private Placement - Reconciliat

Private Placement - Reconciliation of the Subscription Receivable and Forward Purchase Derivative Liabilities (Details) - USD ($) $ in Thousands		3 Months Ended
	Sep. 29, 2023	Mar. 31, 2024	Mar. 31, 2023
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Loss on amendment of forward purchase contracts	$ 24,500
Subscription Receivable
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at December 31, 2023		$ 17,792
Amendment of forward purchase contracts		2,764
Change in fair value of forward purchase derivative liabilities		0
Loss on amendment of forward purchase contracts		4,639
Ending balance at March 31, 2024		10,389
Forward Purchase Derivative Liabilities
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at December 31, 2023		15,804
Amendment of forward purchase contracts		(1,418)
Change in fair value of forward purchase derivative liabilities		(535)	$ 0
Loss on amendment of forward purchase contracts		(3,766)
Ending balance at March 31, 2024		$ 10,085

Warrants - Narrative (Details)

Warrants - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended
	Feb. 09, 2024	Sep. 29, 2023	May 20, 2021	Mar. 31, 2024	Mar. 31, 2023	Sep. 28, 2023	Dec. 31, 2019
Class of Warrant or Right [Line Items]
Proceeds from issuance of warrants		$ 10,210		$ 250	$ 0
Redemption price of warrants (in usd per share)				$ 18
Interest rate				12%
Gain on amendment of PIPE warrant agreement	$ 679			$ 679	$ 0
Fair Value Adjustment of Warrants	429
Proceeds from amendments of warrants	250
First Tranche
Class of Warrant or Right [Line Items]
Proceeds from warrant investors, warrant amendment option	300
Second Tranche
Class of Warrant or Right [Line Items]
Proceeds from warrant investors, warrant amendment option	$ 300
VWAP trailing period	5 days
Convertible Debt | Line of Credit
Class of Warrant or Right [Line Items]
Working capital loan						$ 800
Convertible 12% promissory notes
Class of Warrant or Right [Line Items]
Interest rate				12%
Convertible 12% promissory notes | Convertible Debt
Class of Warrant or Right [Line Items]
Interest rate				12%
Public warrants
Class of Warrant or Right [Line Items]
Warrant, exercise price (in dollars per share)			$ 11.50
Period before warrants become exercisable			30 days
Warrant term			5 years
Public warrants | Graf Acquisition Partners IV LLC
Class of Warrant or Right [Line Items]
Warrants issued (in shares)			3,432,286
Public warrants | Common Stock
Class of Warrant or Right [Line Items]
Closing price required to redeem warrants (in dollars per share)			$ 18
Private warrants | Graf Acquisition Partners IV LLC
Class of Warrant or Right [Line Items]
Warrants issued (in shares)			4,721,533
Warrant, exercise price (in dollars per share)			$ 11.50
SPA warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)				1,000,000
Warrant, exercise price (in dollars per share)				$ 11.50
Working capital warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)		523,140
Warrant, exercise price (in dollars per share)		$ 11.50
PIPE warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)		10,209,994
Warrant term		5 years
Proceeds from issuance of warrants		$ 10,200
Purchase price (usd per share)		$ 1
Period before warrant adjustment		180 days
PIPE warrants | First Tranche
Class of Warrant or Right [Line Items]
Warrant, exercise price (in dollars per share)		$ 10
PIPE warrants | Second Tranche
Class of Warrant or Right [Line Items]
Warrant, exercise price (in dollars per share)		12.50
PIPE warrants | Third Tranche
Class of Warrant or Right [Line Items]
Warrant, exercise price (in dollars per share)		15
PIPE warrants | Minimum
Class of Warrant or Right [Line Items]
Cashless exchange, stock price trigger (in USD per share)		$ 1.50
Convertible bridge loan warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)				1,250,000
Conversion ratio				1
Warrant term				5 years
Convertible bridge loan warrants | Minimum
Class of Warrant or Right [Line Items]
Warrant, exercise price (in dollars per share)				$ 1.50
Convertible bridge loan warrants | Maximum
Class of Warrant or Right [Line Items]
Warrant, exercise price (in dollars per share)				$ 2
Convertible 12% promissory note warrants
Class of Warrant or Right [Line Items]
Conversion ratio				1
Warrant, exercise price (in dollars per share)				$ 2
Warrant term				5 years
Convertible 12% promissory note warrants | Convertible Debt
Class of Warrant or Right [Line Items]
Warrants issued (in shares)							660,000

Warrants - PIPE Warrant Amendme

Warrants - PIPE Warrant Amendment (Details) - USD ($) $ in Thousands		3 Months Ended
	Feb. 09, 2024	Mar. 31, 2024	Mar. 31, 2023
Warrants [Abstract]
Cash proceeds	$ 250
Reduction in PIPE Warrant derivative liability	429
Gain on amendment of PIPE warrant agreement	$ 679	$ 679	$ 0

Convertible Notes - Narrative (

Convertible Notes - Narrative (Details)

1 Months Ended

2 Months Ended

3 Months Ended

Apr. 25, 2024 USD ($)

Apr. 19, 2024 USD ($) shares

Apr. 18, 2024 USD ($)

Apr. 17, 2024 USD ($)

Apr. 12, 2024 USD ($)

Apr. 08, 2024 USD ($)

Sep. 29, 2023 USD ($) shares

Sep. 28, 2023 USD ($) $ / shares shares

May 09, 2024 USD ($)

Apr. 30, 2024 USD ($) d

Mar. 31, 2024 USD ($) holder $ / shares shares

Mar. 31, 2024 USD ($) holder $ / shares shares

Dec. 31, 2019 USD ($) shares

Mar. 31, 2024 USD ($) holder $ / shares shares

Mar. 31, 2023 USD ($)

Sep. 30, 2023

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 10,000,000

Interest rate

12%

12%

12%

Converted shares (in shares) | shares

5,579,266

Stock converted, reverse recapitalization (in shares) | shares

2,278,598

Interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)

$ 1,069,000

$ 34,000

Loss on issuance of convertible notes

$ 729,000

0

Convertible bridge loan warrants

Debt Instrument [Line Items]

Warrants issued (in shares) | shares

1,250,000

1,250,000

1,250,000

Fair value of warrants

$ 1,400,000

$ 1,400,000

$ 1,400,000

Bridge Loan

Debt Instrument [Line Items]

Borrowing term

15 days

Premium, percentage

7.50%

7.50%

7.50%

Legacy NKGen Common Stock

Debt Instrument [Line Items]

Converted shares (in shares) | shares

5,579,266

Related Party

Debt Instrument [Line Items]

Interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)

$ 698,000

33,000

Loss on issuance of convertible notes

74,000

0

Related Party | Convertible Debt | Convertible bridge loan warrants

Debt Instrument [Line Items]

Warrants issued (in shares) | shares

400,000

2019 Related Party Convertible Notes

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 17,300,000

2019 Related Party Convertible Notes | Convertible Debt

Debt Instrument [Line Items]

Interest rate

1.70%

2019 Related Party Convertible Notes | Related Party

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 400,000

2019 Convertible Notes | Convertible Debt

Debt Instrument [Line Items]

Interest rate

1.70%

2023 Convertible Notes | Convertible Debt

Debt Instrument [Line Items]

Interest rate

4.60%

2023 Related Party Convertible Notes | Convertible Debt

Debt Instrument [Line Items]

Interest rate

4.60%

Senior convertible notes’ shares | Related Party | Convertible Debt

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 10,000,000

Interest rate

5%

Borrowing term

4 years

Paid in kind interest rate

0.080

Conversion price (in dollars per share) | $ / shares

$ 10

Exercise term

2 years 6 months

Minimum holding period post exercise

6 months

Interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)

200,000

2024 Convertible Bridge Loans | Bridge Loan

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 300,000

Interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)

200,000

Accretion expense

200,000

2024 Convertible Bridge Loans | Bridge Loan | Subsequent Event

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 100,000

Working capital loan

100,000

2024 Convertible Bridge Loans | Convertible Debt | Subsequent Event

Debt Instrument [Line Items]

Repayments of convertible debt

$ 300,000

Number of convertible debt loans repaid | d

2

2024 Related Party Convertible Bridge Loans | Bridge Loan | Subsequent Event

Debt Instrument [Line Items]

Borrowing term

90 days

2024 Related Party Convertible Bridge Loans | Convertible Debt | Subsequent Event

Debt Instrument [Line Items]

Repayments of convertible debt

$ 500,000

2024 Related Party Convertible Bridge Loans | Related Party | Bridge Loan

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 400,000

Interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)

400,000

2024 Related Party Convertible Bridge Loans | Related Party | Bridge Loan | Subsequent Event

Debt Instrument [Line Items]

Financing event threshold, debt maturity

$ 5,000,000

Repayments of convertible debt

$ 500,000

Convertible bridge loans

Debt Instrument [Line Items]

Proceeds from convertible debt

700,000

0

Loss on issuance of convertible notes

$ 700,000

Convertible bridge loans | Bridge Loan

Debt Instrument [Line Items]

Borrowing term

60 days

Interest expense (including related party amounts of $698 and $33 for the three months ended March 31, 2024 and 2023, respectively)

0

Premium, percentage

20%

20%

20%

Discount of stock price

0.150

0.150

0.150

VWAP trailing period

10 days

10 days

10 days

Conversion, common stock price ceiling (in usd per share) | $ / shares

$ 2

$ 2

$ 2

Warrants issued (in shares) | shares

7,334

7,334

7,334

Convertible bridge loans | Bridge Loan | Maximum

Debt Instrument [Line Items]

Financing event threshold, debt maturity

$ 10,000,000

$ 10,000,000

$ 10,000,000

Convertible bridge loans | Bridge Loan | Minimum

Debt Instrument [Line Items]

Financing event threshold, debt maturity

$ 5,000,000

$ 5,000,000

5,000,000

Convertible bridge loans | Bridge Loan | Subsequent Event

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 300,000

Borrowing term

90 days

Premium, percentage

24.60%

Financing event threshold, debt maturity

$ 5,000,000

Stock issued during period (in shares) | shares

16,667

Convertible bridge loans | Convertible Debt

Debt Instrument [Line Items]

Proceeds from convertible debt

700,000

Convertible bridge loans | Convertible Debt | Subsequent Event

Debt Instrument [Line Items]

Borrowing term

90 days

Repayments of convertible debt

100,000

Working capital loan

$ 100,000

Convertible 12% promissory notes

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 574,000

0

Interest rate

12%

12%

12%

Change in fair value of convertible debt

$ 478,000

$ 0

Convertible 12% promissory notes | Subsequent Event

Debt Instrument [Line Items]

Repayments of convertible debt

$ 400,000

Convertible 12% promissory notes | Convertible Debt

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 600,000

Interest rate

12%

12%

12%

Borrowing term

1 year

Conversion price (in dollars per share) | $ / shares

$ 2

$ 2

$ 2

Number of FPA holders | holder

2

2

2

Issued discount

$ 100,000

$ 100,000

$ 100,000

Guaranteed interest, period

12 months

12 months

12 months

Stock issued during period (in shares) | shares

500,000

Convertible 12% promissory notes | Convertible Debt | Subsequent Event

Debt Instrument [Line Items]

Repayments of convertible debt

$ 800,000

Convertible Bridge Loans, Convertible Bridge Loan Warrants And Consideration Shares | Convertible Debt

Debt Instrument [Line Items]

Proceeds from convertible debt

$ 700,000

Loss on issuance of convertible notes

700,000

Promissory note agreement

$ 1,400,000

$ 1,400,000

$ 1,400,000

Convertible Notes - Reconciliat

Convertible Notes - Reconciliation of Senior Convertible Notes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Debt Instrument [Roll Forward]
Paid-in-kind interest	$ 949	$ 33
Related Party
Debt Instrument [Roll Forward]
Paid-in-kind interest	698	$ 33
Senior Notes | Convertible Notes Payable | Related Party
Debt Instrument [Roll Forward]
Beginning Balance	9,930
Amortization of discount	11
Paid-in-kind interest	206
Ending Balance	$ 10,147

Debt (Details)

Debt (Details) - USD ($)	1 Months Ended			3 Months Ended		4 Months Ended
	Apr. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2024	Mar. 31, 2023	Apr. 30, 2023	Dec. 31, 2023
Debt Instrument [Line Items]
Interest rate		12%		12%
Issuance fees		$ 100,000		$ 100,000			$ 100,000
Interest expense				1,069,000	$ 34,000
Proceeds from related party loans				0	4,500,000	$ 5,000,000
Proceeds from issuance of bridge loans				$ 200,000	0
Bridge Loan
Debt Instrument [Line Items]
Line of credit borrowing term		15 days
Proceeds from issuance of bridge loans		$ 200,000
Premium, percentage		7.50%		7.50%
Related Party
Debt Instrument [Line Items]
Interest expense				$ 698,000	33,000
Related Party | Loans Payable
Debt Instrument [Line Items]
Interest payable		$ 100,000		$ 100,000			$ 200,000
Related Party Loans | Loans Payable
Debt Instrument [Line Items]
Interest rate						4.60%
Revolving Credit Facility | Commercial Bank Credit Facility | Line of Credit
Debt Instrument [Line Items]
Revolving line of credit			$ 5,000,000
Line of credit borrowing term			1 year
Interest rate			7.50%
Issuance fees			$ 100,000
Restricted cash balance requirement			300,000
Minimum deposit balance			$ 15,000,000
Interest rate for the revolving line of credit		8.20%		8.20%
Repayments on paycheck protection loan				$ 4,900,000
Interest expense				$ 100,000	$ 0
Revolving Credit Facility | Commercial Bank Credit Facility | Line of Credit | Subsequent Event
Debt Instrument [Line Items]
Repayments of convertible debt	$ 100,000
Revolving Credit Facility | Commercial Bank Credit Facility | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Line of Credit
Debt Instrument [Line Items]
Basis spread interest rate on secured overnight financing rate			2.90%

Related-Party Transactions (Det

Related-Party Transactions (Details)		3 Months Ended
	Apr. 14, 2023 d $ / shares shares	Mar. 31, 2024 USD ($) shares	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) shares	Sep. 29, 2023 shares	Dec. 31, 2019 shares
Related Party Transaction [Line Items]
Common stock outstanding (in shares)		22,388,976		21,888,976	21,888,976
Award trading restriction period	2 years
Research and development expense | $		$ 3,236,000	$ 3,599,000
Accounts payable | $		$ 12,835,000		$ 11,040,000
Convertible bridge loan warrants
Related Party Transaction [Line Items]
Warrants issued (in shares)		1,250,000
Related Party | Convertible bridge loan warrants | Convertible Debt
Related Party Transaction [Line Items]
Warrants issued (in shares)						400,000
Amended And Restated Sponsor Support Lockup Agreement | Related Party | Graf Acquisition Partners IV LLC
Related Party Transaction [Line Items]
Common stock outstanding (in shares)	4,290,375
Shares forfeited (in shares)	1,773,631
Restricted shares subject to vesting conditions (in shares)	1,173,631
Shares were not forfeited, did not become restricted, nor subject to vesting conditions (in shares)	1,343,113
Purchases of Laboratory Supplies | Related Party
Related Party Transaction [Line Items]
Research and development expense | $		$ 0	$ 0
Accounts payable | $		$ 0		$ 600,000
Deferred Founder Shares | Amended And Restated Sponsor Support Lockup Agreement | Related Party | Graf Acquisition Partners IV LLC
Related Party Transaction [Line Items]
Vesting period	5 years
Deferred Founder Shares | Trance One | Amended And Restated Sponsor Support Lockup Agreement | Related Party | Graf Acquisition Partners IV LLC
Related Party Transaction [Line Items]
Share price trigger (in USD per share) | $ / shares	$ 14
Threshold trading days | d	20
Threshold consecutive trading days | d	30
Shares vested (in shares)	873,631
Deferred Founder Shares | Tranche Two | Amended And Restated Sponsor Support Lockup Agreement | Related Party | Graf Acquisition Partners IV LLC
Related Party Transaction [Line Items]
Share price trigger (in USD per share) | $ / shares	$ 20
Threshold trading days | d	20
Threshold consecutive trading days | d	30
Shares vested (in shares)	300,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Schedule of Fair Value Hierarchy (Details) $ in Thousands	Mar. 31, 2024 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible notes	$ 728
Liabilities measured at fair value	$ 34,187
Interest rate	12%
Convertible 12% promissory notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate	12%
Convertible 12% promissory notes | Convertible Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate	12%
Private warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	$ 803
Working capital warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	89
PIPE warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	19,704
Convertible bridge loan warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	1,822
Convertible 12% promissory note warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	942
Forward Purchase Derivative Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	10,085
Consideration Shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	14
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible notes	0
Liabilities measured at fair value	14
Level 1 | Private warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 1 | Working capital warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 1 | PIPE warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 1 | Convertible bridge loan warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 1 | Convertible 12% promissory note warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 1 | Forward Purchase Derivative Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 1 | Consideration Shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	14
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible notes	0
Liabilities measured at fair value	0
Level 2 | Private warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 2 | Working capital warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 2 | PIPE warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 2 | Convertible bridge loan warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 2 | Convertible 12% promissory note warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 2 | Forward Purchase Derivative Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 2 | Consideration Shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible notes	728
Liabilities measured at fair value	34,173
Level 3 | Private warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	803
Level 3 | Working capital warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	89
Level 3 | PIPE warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	19,704
Level 3 | Convertible bridge loan warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	1,822
Level 3 | Convertible 12% promissory note warrants
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	942
Level 3 | Forward Purchase Derivative Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	10,085
Level 3 | Consideration Shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability	$ 0

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Narrative (Details) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended
	Sep. 29, 2023 USD ($) $ / shares shares	Mar. 31, 2024 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Mar. 26, 2024	Dec. 31, 2023 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Stock converted, reverse recapitalization (in shares) | shares	2,278,598
Conversion of legacy NKGen convertible promissory notes	$ 18,913
Stock converted, reverse recapitalization (in USD per share) | $ / shares	$ 8.30
Interest rate		12%	12%
Forward purchase derivative liabilities	$ 20,200	$ 10,085	$ 10,085			$ 15,804
Proceeds from convertible debt	$ 10,000
Loss on issuance of convertible notes			729	$ 0
Forward Purchase Derivative Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Forward purchase derivative liabilities		10,100	10,100
Derivative liability		10,085	10,085
Convertible 12% promissory note warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability		942	942
Convertible 12% promissory note warrants | Relative Fair Value At Initial Recognition
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt securities		300	300
Convertible 12% promissory note warrants | Residual Fair Value
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt securities		$ 900	$ 900
Convertible 12% promissory note warrants | Convertible Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate		12%	12%
Convertible bridge loan warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability		$ 1,822	$ 1,822
Convertible bridge loan warrants | Relative Fair Value At Initial Recognition
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability		1,400	1,400
Convertible bridge loan warrants | Residual Fair Value
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative liability		100	100
Convertible 12% promissory notes | Relative Fair Value At Initial Recognition
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Promissory note agreement		600	600
Debt securities		300	300
Convertible 12% promissory notes | Residual Fair Value
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Debt securities		$ 700	$ 700
Dividend yield (per share)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Private warrants and working capital warrants unobservable input						0
Legacy Convertible Notes | Nonrelated Party
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expense associated with change in fair value				1,500
Convertible 12% promissory notes
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate		12%	12%
Proceeds from convertible debt			$ 574	0
Convertible 12% promissory notes | Convertible Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate		12%	12%		12%
Convertible 12% promissory notes | Convertible Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate		12%	12%
Proceeds from convertible debt		$ 600
Convertible 12% promissory note warrants | Convertible Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate		12%	12%
Convertible 12% promissory note warrants | Convertible Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Interest rate		12%	12%
Convertible bridge loans
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Proceeds from convertible debt			$ 700	$ 0
Loss on issuance of convertible notes			700
Convertible bridge loans | Convertible Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Proceeds from convertible debt			$ 700

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Convertible 12% Promissory Notes (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance as of December 31, 2023	$ 25,758,000
Issuance	1,747,000
Change in fair value	(3,716,000)
Balance as of March 31, 2024	$ 23,360,000
Interest rate	12%
Convertible 12% promissory notes
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Interest rate	12%
Convertible 12% promissory notes | Convertible Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance as of December 31, 2023	$ 0
Issuance	250
Change in fair value	478
Balance as of March 31, 2024	$ 728
Interest rate	12%

Fair Value of Financial Instr_6

Fair Value of Financial Instruments - Valuation Assumptions (Details)	Mar. 31, 2024	Feb. 09, 2024	Dec. 31, 2023
Credit spread | PIPE warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.190	0.178	0.127
Credit spread | Convertible 12% promissory notes | Convertible Debt
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.275
Equity volatility | PIPE warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	1.050	1.050	1
Equity volatility | Convertible bridge loan warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	1		1.050
Equity volatility | Private Warrants and Working Capital Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.555		0.353
Equity volatility | Convertible 12% promissory note warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	1		0
Equity volatility | Convertible 12% promissory notes | Convertible Debt
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.450
Dividend yield (per share) | Convertible bridge loan warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0		0
Dividend yield (per share) | Private Warrants and Working Capital Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0		0

Fair Value of Financial Instr_7

Fair Value of Financial Instruments - Derivative Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance December 31, 2023	$ 23,360,000	$ 25,758,000
Issuance	1,747,000
Change in fair value	(3,716,000)
Balance as of March 31, 2024	$ 23,360,000
Interest rate	12%
PIPE Warrants Amendment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value	$ (429,000)
Convertible 12% promissory notes
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Interest rate	12%
Convertible 12% promissory notes | Convertible Debt
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance December 31, 2023	$ 728	0
Issuance	250
Change in fair value	478
Balance as of March 31, 2024	$ 728
Interest rate	12%
Private warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance December 31, 2023	$ 803,000	377,000
Issuance	0
Change in fair value	426,000
Balance as of March 31, 2024	803,000
Private warrants | PIPE Warrants Amendment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value	0
Working capital warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance December 31, 2023	89,000	42,000
Issuance	0
Change in fair value	47,000
Balance as of March 31, 2024	89,000
Working capital warrants | PIPE Warrants Amendment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value	0
Convertible bridge loan warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance December 31, 2023	1,822,000	0
Issuance	1,424,000
Change in fair value	398,000
Balance as of March 31, 2024	1,822,000
Convertible bridge loan warrants | PIPE Warrants Amendment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value	0
Convertible 12% promissory note warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance December 31, 2023	942,000	0
Issuance	323,000
Change in fair value	619,000
Balance as of March 31, 2024	942,000
Convertible 12% promissory note warrants | PIPE Warrants Amendment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value	0
PIPE warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance December 31, 2023	19,704,000	$ 25,339,000
Issuance	0
Change in fair value	(5,206,000)
Balance as of March 31, 2024	19,704,000
PIPE warrants | PIPE Warrants Amendment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value	$ (429,000)

Fair Value of Financial Instr_8

Fair Value of Financial Instruments - Valuation Assumptions of Forward Purchase Derivative Liability (Details) - Forward Purchase Derivative Liabilities	Mar. 31, 2024	Feb. 21, 2024	Jan. 19, 2024	Dec. 31, 2023
Dividend yield (per share)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0	0	0	0
Equity volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	1.200	1.450	1.050	1.150

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) installment $ / shares shares	Dec. 31, 2023 $ / shares shares	Sep. 29, 2023 shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, shares authorized (shares)	500,000,000	500,000,000
Common stock, par value (in USD per share) | $ / shares	$ 0.0001	$ 0.0001
Common stock, shares issued (in shares)	22,388,976	21,888,976
Common stock outstanding (in shares)	22,388,976	21,888,976	21,888,976
Common stock, reserved for future issuance (in shares)	477,611,024
Preferred stock, shares authorized (in shares)	10,000,000
Preferred stock, par value (in USD per share) | $ / shares	$ 0.0001
Preferred stock, shares issued (in shares)	0
Preferred stock, shares outstanding (in shares)	0
Fair value of options vested | $	$ 3.8
Unrecognized stock-based compensation | $	$ 12.4
Employee Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Maximum shares allowed to be issued (as a percent)	3%
ESPP purchase price of common stock, percent of market price (as a percent)	85%
Weighted- average period of recognition	3 years 1 month 6 days
Stock Compensation | 2023 Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Maximum shares allowed to be issued (as a percent)	12%
Stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected dividend yield	0%
Stock options | 2023 Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected dividend yield	0%
Stock options | 2019 Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration period (in years)	10 years
Vesting period	4 years
Vested, expiration period	3 months
Vesting percentage (as a percent)	25%
Number of monthly installments | installment	36
Stock options | 2019 Plan | Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period	3 years
Stock options | 2019 Plan | Minimum | Board Member
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration period (in years)	3 years
Stock options | 2019 Plan | Maximum | Board Member
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration period (in years)	4 years
Vesting period	4 years

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Stock Options Outstanding
Outstanding at beginning of period (in shares) | shares	2,078,986
Granted (in shares) | shares	2,295,000
Forfeited (in shares) | shares	(109,725)
Exercised (in shares) | shares	0
Outstanding at end of period (in shares) | shares	4,264,261
Weighted Average Exercise Price
Outstanding at beginning of period (in USD per share) | $ / shares	$ 6.25
Granted (in USD per share) | $ / shares	1.62
Forfeited (in USD per share) | $ / shares	6.65
Exercised (in USD per share) | $ / shares	0
Outstanding at end of period (in USD per share) | $ / shares	$ 3.75

Stockholders' Equity - Stock Op

Stockholders' Equity - Stock Option Valuation Assumptions (Details) - Stock options	3 Months Ended
	Mar. 31, 2024 $ / shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected dividend yield	0%
2023 Plan
Equity [Abstract]
Common stock fair value (in usd per share)	$ 1.62
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock fair value (in usd per share)	$ 1.62
Risk-free interest rate	4.20%
Expected volatility	92%
Expected term (in years)	6 years 10 months 24 days
Expected dividend yield	0%

Stockholders' Equity - Schedu_2

Stockholders' Equity - Schedule of Stock Options Vested and Expected to Vest (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Number of Stock Options
Outstanding at beginning of period (in shares)	2,078,986
Outstanding at end of period (in shares)	4,264,261	2,078,986
Vested and expected to vest (in shares)	4,264,261
Exercisable (in shares)	1,038,115
Weighted Average Remaining Contractual Life (Years)
Outstanding as of December 31, 2023	3 years 11 months 19 days	8 years 10 months 9 days
Outstanding as of March 31, 2024	3 years 11 months 19 days	8 years 10 months 9 days
SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1	3 years 11 months 19 days
Exercisable (years)	8 years 8 months 4 days
Weighted- Average Exercise Price
Outstanding at end of period (in USD per share)	$ 3.75	$ 6.25
Outstanding at end of period (in USD per share)	3.75	$ 6.25
Vested and expected to vest (in USD per share)	3.75
Exercisable (in USD per share)	$ 4.31
Total Aggregate Intrinsic Value (in thousands)
Outstanding at beginning of period	$ 825	$ 317
Outstanding at end of period	825	$ 317
Vested and expected to vest	825
Exercisable	$ 289

Stockholders' Equity - Schedu_3

Stockholders' Equity - Schedule of Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 1,117	$ 1,258
Research and development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	145	330
General and administrative
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 972	$ 928

Property and Equipment, net - S

Property and Equipment, net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 18,199	$ 18,284
Less: Accumulated depreciation	(4,063)	(3,825)
Property and equipment, net	14,136	14,459
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,025	5,025
Buildings
Property, Plant and Equipment [Line Items]
Useful Life	40 years
Property and equipment, gross	$ 8,325	8,325
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Useful Life	7 years
Property and equipment, gross	$ 749	749
Lab equipment
Property, Plant and Equipment [Line Items]
Useful Life	5 years
Property and equipment, gross	$ 4,004	4,004
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 52	52
Office equipment
Property, Plant and Equipment [Line Items]
Useful Life	5 years
Property and equipment, gross	$ 17	17
Vehicles
Property, Plant and Equipment [Line Items]
Useful Life	5 years
Property and equipment, gross	$ 27	$ 112

Property and Equipment, net - N

Property and Equipment, net - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 300,000	$ 300,000
Loss on sale of property and equipment, net	$ (8,000)	$ 0

Additional Balance Sheet Info_3

Additional Balance Sheet Information - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Prepaid expenses	$ 1,250	$ 1,565
Other receivables	26	26
Revolving line of credit issuance fees	47	47
Other	0	16
Prepaid expenses and other current assets	$ 1,323	$ 1,654

Additional Balance Sheet Info_4

Additional Balance Sheet Information - Schedule of Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Accounts payable	$ 12,835	$ 11,040
Accrued liabilities	1,630	1,360
Employee compensation	733	911
Other	115	84
Accounts payable and accrued expenses	$ 15,313	$ 13,395

Collaboration Agreement (Detail

Collaboration Agreement (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Reductions to research and development expenses	$ 0.1	$ 0.1

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details)	23 Months Ended
	Aug. 31, 2023 USD ($)	Mar. 31, 2024 USD ($) country	Dec. 31, 2023 USD ($)	Nov. 09, 2023	Oct. 31, 2021	Feb. 28, 2018
Other Commitments [Line Items]
Term of lease				3 years	2 years	5 years
Renewal extension period					2 years
Right of use asset, gross		$ 500,000
Operating lease, accumulated amortization		100,000
Total operating lease liability		500,000
Operating lease liability, current		154,000	$ 0
Operating lease liability, non-current		$ 348,000	0
Remaining lease term		2 years 9 months 18 days
Payments for license agreement	$ 1,000,000
Accrued litigation liability		$ 0	$ 0
Weighted-average estimated incremental borrowing rate		22.40%
NKMAX
Other Commitments [Line Items]
Number of countries | country		4
NKMAX | UNITED STATES
Other Commitments [Line Items]
Milestone payment, after regulatory approval		$ 5,000,000
NKMAX | European Union
Other Commitments [Line Items]
Milestone payment, after regulatory approval		4,000,000
NKMAX | Country A
Other Commitments [Line Items]
Milestone payment, after regulatory approval		1,000,000
NKMAX | Country B
Other Commitments [Line Items]
Milestone payment, after regulatory approval		1,000,000
NKMAX | Country C
Other Commitments [Line Items]
Milestone payment, after regulatory approval		1,000,000
NKMAX | Country D
Other Commitments [Line Items]
Milestone payment, after regulatory approval		$ 1,000,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Rental Payments for Operating Leases (Details) $ in Thousands	Mar. 31, 2024 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2024 (excluding the three months ended 3/31/2024)	$ 176
2025	242
2026	249
Total operating lease liability	$ 667

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Tax Disclosure [Abstract]
Effective tax rate	0%	0%

Subsequent Events (Details)

Subsequent Events (Details) $ / shares in Units, $ in Thousands

1 Months Ended

2 Months Ended

3 Months Ended

8 Months Ended

May 09, 2024 USD ($) $ / shares shares

May 07, 2024 USD ($) $ / shares shares

May 06, 2024 USD ($) $ / shares shares

May 01, 2024 USD ($) $ / shares shares

Apr. 30, 2024 USD ($) $ / shares shares

Apr. 28, 2024 USD ($) $ / shares shares

Apr. 25, 2024 USD ($)

Apr. 19, 2024 USD ($) $ / shares shares

Apr. 18, 2024 USD ($) repayment

Apr. 17, 2024 USD ($)

Apr. 12, 2024 USD ($) shares

Apr. 11, 2024 $ / shares shares

Apr. 08, 2024 USD ($)

Apr. 05, 2024 USD ($) tranche $ / shares shares

Apr. 01, 2024 USD ($) $ / shares shares

Sep. 29, 2023 USD ($)

Apr. 30, 2024 USD ($) $ / shares shares

Mar. 31, 2024

Jun. 30, 2023 USD ($)

Mar. 31, 2024 USD ($)

Mar. 31, 2024 USD ($)

Mar. 31, 2023 USD ($)

Dec. 31, 2024 USD ($) tranche shares

Dec. 31, 2024 USD ($) tranche shares

Mar. 26, 2024

Subsequent Event [Line Items]

Interest rate

12%

12%

12%

Proceeds from convertible debt

$ 10,000

Convertible 12% promissory notes

Subsequent Event [Line Items]

Interest rate

12%

12%

12%

Proceeds from convertible debt

$ 574

$ 0

Convertible bridge loans

Subsequent Event [Line Items]

Proceeds from convertible debt

$ 700

$ 0

Subsequent Event

Subsequent Event [Line Items]

Number of repayments on convertible debt | repayment

2

Subsequent Event | Forecast

Subsequent Event [Line Items]

Number of additional convertible notes tranche issues | tranche

3

3

Subsequent Event | Forward Purchase Contract Amendments

Subsequent Event [Line Items]

Initial price ceiling (in usd per share) | $ / shares

$ 1.27

Number of additional shares available (in shares) | shares

1,416,350

248,360

Subsequent Event | Convertible 12% promissory notes

Subsequent Event [Line Items]

Repayments of convertible debt

$ 400

Convertible Debt

Subsequent Event [Line Items]

Borrowing term

3 years

Convertible Debt | Convertible 12% promissory notes

Subsequent Event [Line Items]

Interest rate

12%

12%

12%

12%

Convertible Debt | Subsequent Event | Convertible 12% promissory notes

Subsequent Event [Line Items]

Interest rate

12%

12%

12%

12%

Promissory note agreement

$ 200

$ 300

$ 200

Borrowing term

1 year

1 year

Discount percentage, issued

0.100

Stock issued during period (in shares) | shares

125,000

250,000

Number of securities purchased (in shares) | shares

165,000

330,000

165,000

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

$ 2

$ 2

Repayments of convertible debt

$ 400

Issued discount

$ 100

$ 100

Convertible Debt | Subsequent Event | Convertible 12% promissory notes | FPA Investor

Subsequent Event [Line Items]

Interest rate

12%

Promissory note agreement

$ 200

Borrowing term

1 year

Discount percentage, issued

0.100

Stock issued during period (in shares) | shares

166,667

Number of securities purchased (in shares) | shares

220,000

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

Convertible Debt | Subsequent Event | Convertible 12% promissory notes | Two FPA Investors

Subsequent Event [Line Items]

Interest rate

12%

Stock issued during period (in shares) | shares

416,667

Number of securities purchased (in shares) | shares

550,000

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

Repayment threshold, proceeds received

$ 10,000

Cash consideration

100

Convertible Debt | Subsequent Event | Convertible 12% promissory notes | Related Party

Subsequent Event [Line Items]

Interest rate

12%

Promissory note agreement

$ 400

Borrowing term

1 year

Discount percentage, issued

0.100

Stock issued during period (in shares) | shares

333,333

Number of securities purchased (in shares) | shares

440,000

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

Convertible Debt | Subsequent Event | Convertible 12% promissory notes | First Tranche | Two FPA Investors

Subsequent Event [Line Items]

Repayment threshold, proceeds received

5,000

Convertible Debt | Subsequent Event | Convertible 12% promissory notes | Second Tranche | Two FPA Investors

Subsequent Event [Line Items]

Repayment threshold, proceeds received

$ 5,000

Convertible Debt | Subsequent Event | Convertible Promissory Notes

Subsequent Event [Line Items]

Promissory note agreement

$ 400

Borrowing term

1 year

Stock issued during period (in shares) | shares

250,000

Number of securities purchased (in shares) | shares

330,000

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

Issued discount

$ 100

Convertible Debt | Subsequent Event | Convertible Promissory Notes | Forecast

Subsequent Event [Line Items]

Promissory note agreement

$ 1,100

$ 1,100

Number of additional convertible notes tranche issues | tranche

3

3

Shares, available to be issued (in shares) | shares

750,000

750,000

Number of securities available to be called by warrants (in shares) | shares

990,000

Convertible Debt | Subsequent Event | Convertible Secured Promissory Note

Subsequent Event [Line Items]

Interest rate

2.90%

Promissory note agreement

$ 5,000

Number of securities purchased (in shares) | shares

1,000,000

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

Number of trances | tranche

2

Conversion price (in dollars per share) | $ / shares

$ 2

Number of additional shares issuable (in shares) | shares

833,333,000,000

Number of additional shares issuable in transaction

$ 2,500

VWAP trailing period

5 days

Convertible Debt | Subsequent Event | Convertible Secured Promissory Note | First Tranche

Subsequent Event [Line Items]

Promissory note agreement

$ 1,000

Convertible Debt | Subsequent Event | Convertible Secured Promissory Note | Second Tranche

Subsequent Event [Line Items]

Promissory note agreement

$ 4,000

Convertible Debt | Subsequent Event | Zero Coupon Convertible Promissory Note

Subsequent Event [Line Items]

Interest rate

0%

Promissory note agreement

$ 600

Borrowing term

1 year

Stock issued during period (in shares) | shares

416,667

Number of securities purchased (in shares) | shares

550,000

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

Issued discount

$ 100

Convertible Debt | Subsequent Event | Zero Coupon Convertible Promissory Note | Forecast

Subsequent Event [Line Items]

Interest rate

0%

0%

Promissory note agreement

$ 1,800

$ 1,800

Number of additional convertible notes tranche issues | tranche

3

3

Shares, available to be issued (in shares) | shares

1,250,000

1,250,000

Number of securities available to be called by warrants (in shares) | shares

1,650,000

Bridge Loan

Subsequent Event [Line Items]

Borrowing term

15 days

Premium, percentage

7.50%

7.50%

7.50%

Bridge Loan | 2024 Related Party Convertible Bridge Loans | Related Party

Subsequent Event [Line Items]

Proceeds from convertible debt

$ 400

Bridge Loan | Convertible bridge loans

Subsequent Event [Line Items]

Borrowing term

60 days

Premium, percentage

20%

20%

20%

Bridge Loan | 2024 Convertible Bridge Loans

Subsequent Event [Line Items]

Proceeds from convertible debt

$ 300

Bridge Loan | Subsequent Event | 2024 Related Party Convertible Bridge Loans

Subsequent Event [Line Items]

Borrowing term

90 days

Bridge Loan | Subsequent Event | 2024 Related Party Convertible Bridge Loans | Related Party

Subsequent Event [Line Items]

Repayments of convertible debt

$ 500

Financing event threshold, debt maturity

$ (5,000)

Bridge Loan | Subsequent Event | Convertible bridge loans

Subsequent Event [Line Items]

Borrowing term

90 days

Stock issued during period (in shares) | shares

16,667

Number of securities purchased (in shares) | shares

22,000

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

Financing event threshold, debt maturity

$ (5,000)

Proceeds from convertible debt

$ 300

Premium, percentage

24.60%

Bridge Loan | Subsequent Event | 2024 Convertible Bridge Loans

Subsequent Event [Line Items]

Proceeds from convertible debt

$ 100

Working capital loan

$ 100

First Issuance | Convertible Debt | Subsequent Event | Convertible 12% promissory notes

Subsequent Event [Line Items]

Interest rate

12%

Promissory note agreement

$ 200

Borrowing term

1 year

Discount percentage, issued

0.100

Stock issued during period (in shares) | shares

166,667

Number of securities purchased (in shares) | shares

220,000

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

Second Issuance | Convertible Debt | Subsequent Event | Convertible 12% promissory notes

Subsequent Event [Line Items]

Interest rate

12%

Promissory note agreement

$ 100

Borrowing term

1 year

Stock issued during period (in shares) | shares

101,461

Number of securities purchased (in shares) | shares

133,929

Warrant, exercise price (in dollars per share) | $ / shares

$ 2

Issued discount

$ 100

Revolving Credit Facility | Line of Credit | Commercial Bank Credit Facility

Subsequent Event [Line Items]

Interest rate

7.50%

Borrowing term

1 year

Revolving line of credit

$ 5,000

Revolving Credit Facility | Line of Credit | Subsequent Event | Commercial Bank Credit Facility

Subsequent Event [Line Items]

Repayments of convertible debt

$ 100