Prime Medicine (PRME) 10-K 1 Mar 24 2023 FY Annual report Financial data

Cover

Cover - USD ($)	12 Months Ended
	Dec. 31, 2023	Feb. 23, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-41536
Entity Registrant Name	PRIME MEDICINE, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	84-3097762
Entity Address, Address Line One	21 Erie Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	(617)
Local Phone Number	564-0013
Title of 12(b) Security	Common stock, par value $0.00001 per share
Trading Symbol	PRME
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 603,127,652
Entity Common Stock, Shares Outstanding		119,939,247
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement for its 2024 Annual Meeting of Stockholders to be filed pursuant to Regulation 14A within 120 days of the end of the registrant’s fiscal year ended December 31, 2023 are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein.
Entity Central Index Key	0001894562
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2023
Audit Information [Abstract]
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	Boston, Massachusetts
Auditor Firm ID	238

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands		Dec. 31, 2023	Dec. 31, 2022
Cash and cash equivalents
Total cash, and cash equivalents		$ 41,574	$ 187,620
Prepaid expenses		19,057	2,451
Other current assets		2,254	246
Total current assets		142,976	296,618
Property and equipment, net		22,659	19,009
Operating lease right-of-use assets		13,941	29,545
Restricted cash		13,496	13,496
Other assets		779	1,646
Total assets		193,851	360,314
Current liabilities:
Accounts payable		19,537	4,332
Accrued expenses and other current liabilities	[1]	14,110	10,688
Accrued settlement payment — related party		13,500	0
Operating lease liability		9,276	11,694
Total current liabilities		56,423	26,714
Operating lease liability, net of current		4,357	17,051
Non current deferred tax liability		0	279
Total liabilities		60,780	44,044
Commitments and contingencies (Note 12)
Stockholders’ equity
Common stock, par value of $0.00001 per share; 775,000,000 shares authorized; 97,377,121 and 97,209,213 shares issued and outstanding as of December 31, 2023 and 2022, respectively		2	2
Additional paid-in capital		624,414	609,849
Accumulated other comprehensive loss		(15)	(384)
Accumulated deficit		(491,330)	(293,197)
Total stockholders’ equity		133,071	316,270
Total liabilities and stockholders’ equity		193,851	360,314
Nonrelated Party
Cash and cash equivalents
Short-term investments		74,639	98,467
Related Party
Cash and cash equivalents
Short-term investments		$ 5,452	7,834
Current liabilities:
Accrued expenses and other current liabilities			$ 300
[1] Includes related party amount of $0.3 million as of December 31, 2022.

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands		Dec. 31, 2023	Dec. 31, 2022
Common stock, par value (in dollars per share)		$ 0.00001	$ 0.00001
Common stock, shares authorized (in shares)		775,000,000	775,000,000
Common stock, shares issued (in shares)		97,377,121	97,209,213
Common stock, shares outstanding (in shares)		97,377,121	97,209,213
Accrued expenses and other current liabilities	[1]	$ 14,110	$ 10,688
Related Party
Accrued expenses and other current liabilities			$ 300
[1] Includes related party amount of $0.3 million as of December 31, 2022.

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022
Operating expenses:
Research and development	[1]	$ 147,905	$ 86,725
Settlement payment — related party		13,500	0
General and administrative		43,387	29,819
Total operating expenses		204,792	116,544
Loss from operations		(204,792)	(116,544)
Other income (expense):
Change in fair value of short-term investment — related party		(2,382)	(8,128)
Other income, net		8,762	1,903
Total other income (expense), net		6,380	(6,225)
Net loss before income taxes		(198,412)	(122,769)
Benefit from income taxes		279	948
Net loss		(198,133)	(121,821)
Cumulative dividend on preferred stock		0	(20,193)
Net loss attributable to common stockholders, basic		(198,133)	(142,014)
Net loss attributable to common stockholders, diluted		$ (198,133)	$ (142,014)
Net loss per share attributable to common stockholders, basic (in dollars per share)		$ (2.18)	$ (4.19)
Net loss per share attributable to common stockholders, diluted (in dollars per share)		$ (2.18)	$ (4.19)
Weighted-average common shares outstanding, diluted (in shares)		90,969,327	33,891,264
Weighted-average common shares outstanding, basic (in shares)		90,969,327	33,891,264
Comprehensive loss:
Net loss		$ (198,133)	$ (121,821)
Change in unrealized loss on investments, net of tax		369	(357)
Comprehensive loss		$ (197,764)	$ (122,178)
[1] Includes related party amounts of $0.6 million and $0.7 million for the years ended December 31, 2023 and 2022, respectively.

CONSOLIDATED STATEMENTS OF OP_2

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022
Research and development	[1]	$ 147,905	$ 86,725
Research and development | Related Party
Research and development		$ 600	$ 700
[1] Includes related party amounts of $0.6 million and $0.7 million for the years ended December 31, 2023 and 2022, respectively.

CONSOLIDATED STATEMENTS OF REDE

CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE AND CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($)	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Series A Redeemable Convertible Preferred Stock	Series B Convertible Preferred Stock
Beginning balance (in shares) at Dec. 31, 2021						115,761,842	45,658,957
Beginning balance at Dec. 31, 2021						$ 196,157,000	$ 199,643,000
Temporary Equity [Abstract]
Conversion of convertible preferred stock to common stock upon closing of initial public offering (in shares)						(115,761,842)	(45,658,957)
Conversion of convertible preferred stock to common stock upon closing of initial public offering						$ (196,157,000)	$ (199,643,000)
Ending balance (in shares) at Dec. 31, 2022						0	0
Ending balance at Dec. 31, 2022						$ 0	$ 0
Beginning balance (in shares) at Dec. 31, 2021		32,413,860
Beginning balance at Dec. 31, 2021	$ (156,240,000)	$ 0	$ 15,163,000	$ (27,000)	$ (171,376,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		59,774
Issuance of common stock upon exercise of stock options	219,000		219,000
Reclassification of forward contract — related party	12,020,000	$ 1,101,525	12,020,000
Conversion of convertible preferred stock to common stock upon closing of initial public offering (in shares)		51,923,758
Conversion of convertible preferred stock to common stock upon closing of initial public offering	395,801,000	$ 1,000	395,800,000
Issuance of common stock from initial public offering, net of issuance costs and underwriting fees (in shares)		11,721,456
Issuance of common stock from initial public offering, net of issuance costs and underwriting fees of $5.1 million	180,189,000	$ 1,000	180,188,000
Repurchase of unvested restricted common stock (in shares)		(11,160)
Stock-based compensation expense	6,459,000		6,459,000
Change in unrealized loss on investments, net of tax	(357,000)			(357,000)
Net loss	$ (121,821,000)				(121,821,000)
Ending balance (in shares) at Dec. 31, 2022	97,209,213	97,209,213
Ending balance at Dec. 31, 2022	$ 316,270,000	$ 2,000	609,849,000	(384,000)	(293,197,000)
Ending balance (in shares) at Dec. 31, 2023						0	0
Ending balance at Dec. 31, 2023						$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		167,908
Issuance of common stock upon exercise of stock options	655,000		655,000
Stock-based compensation expense	13,910,000		13,910,000
Change in unrealized loss on investments, net of tax	369,000			369,000
Net loss	$ (198,133,000)				(198,133,000)
Ending balance (in shares) at Dec. 31, 2023	97,377,121	97,377,121
Ending balance at Dec. 31, 2023	$ 133,071,000	$ 2,000	$ 624,414,000	$ (15,000)	$ (491,330,000)

CONSOLIDATED STATEMENTS OF RE_2

CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE AND CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Common Stock
Issuance costs	$ 5,100

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows used in operating activities:
Net loss	$ (198,133)	$ (121,821)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	13,910	6,459
Non cash lease expense	12,788	9,790
Depreciation expense	4,653	2,224
Change in fair value of short-term investment — related party	2,382	8,128
Loss on disposal of property and equipment	28	8
Amortization of premiums and discount on short-term investments	(3,408)	(250)
Deferred income taxes	(279)	(964)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(9,455)	(1,738)
Accounts payable	9,140	2,458
Accrued expenses and other current liabilities	1,758	(25,873)
Accrued settlement payment — related party	13,500	0
Lease liability	(12,296)	(10,248)
Net cash used in operating activities	(165,412)	(131,827)
Cash flows provided by (used in) investing activities:
Maturities of investments	132,556	93,000
Purchases of investments	(104,951)	(123,336)
Purchases of property and equipment	(8,724)	(16,095)
Payments of security deposits	(170)	(665)
Net cash provided by (used in) investing activities	18,711	(47,096)
Cash flows provided by financing activities:
Net proceeds from stock option exercises	655	219
Proceeds from initial public offering, net of underwrites discounts and commissions and deferred offering costs	0	185,317
Payments of deferred offering costs	0	(4,042)
Net cash provided by financing activities	655	181,494
Net change in cash, cash equivalents, and restricted cash	(146,046)	2,571
Cash, cash equivalents, and restricted cash at beginning of period	201,116	198,545
Cash, cash equivalents, and restricted cash at end of period	55,070	201,116
Reconciliation of cash, cash equivalents and restricted cash:
Cash, cash equivalents, and restricted cash at end of period	55,070	201,116
Restricted cash	13,496	13,496
Total cash, and cash equivalents	41,574	187,620
Supplemental cash flow information:
Decrease in right-of-use assets due to lease termination	6,081	0
Right-of-use assets obtained in exchange for new operating lease liabilities	3,265	28,590
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued expenses	575	969
Conversion of convertible preferred stock to common stock upon closing of initial public offering	0	395,800
Settlement of related party forward contract	0	12,020
Cash taxes paid	$ 0	$ 141

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	Nature of the Business and Basis of Presentation Prime Medicine, Inc., together with its consolidated subsidiary (the “Company”) is a biotechnology company committed to delivering a new class of differentiated one-time curative genetic therapies to address the widest spectrum of diseases. The Company is deploying Prime Editing technology, which it believe is a versatile, precise, and efficient gene editing technology. The Company was incorporated in the State of Delaware in September 2019. Its principal offices are in Cambridge, Massachusetts. Liquidity and Capital Resources Since its inception, the Company has devoted substantially all of its resources to building its Prime editing platform and advancing development of its portfolio of programs, establishing and protecting its intellectual property, conducting research and development activities, organizing and staffing the company, business planning, raising capital and providing general and administrative support for these operations. To date, the Company has funded its operations primarily with proceeds from sales of preferred stock and from public offerings of its common stock. In February 2024, the Company issued and sold 22,560,001 shares of its common stock, including 3,360,000 shares pursuant to the exercise of the underwriters’ option to purchase additional shares, at a price to the public of $6.25 per share. Further, in lieu of common stock to certain investors, the Company sold pre-funded warrants to purchase 3,200,005 shares of common stock at a public offering price of $6.24999 per pre-funded warrant, which represents the per share public offering price of each share of common stock less the $0.00001 per share exercise price for each pre-funded warrant. As a result of the offering, the Company received approximately $150.9 million in net proceeds, after deducting underwriting discounts, commissions and estimated offering costs of $10.1 million. Since its inception, the Company has incurred substantial losses. As of December 31, 2023, the Company had an accumulated deficit of $491.3 million and expects to generate operating losses and negative operating cash flows for the foreseeable future. As of December 31, 2023, the Company maintains cash, cash equivalents, short-term investments, and related party short-term investments of $121.7 million and expects that this, together with the net proceeds from the February equity offering of approximately $150.9 million, will be sufficient to fund operations for at least the next twelve months from the date of issuance of this Annual Report on Form 10-K. The Company will need additional financing to support its continuing operations and pursue its growth strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through a combination of equity offerings, debt financings, collaborations, strategic alliances and licensing arrangements. The Company may be unable to raise additional funds or enter into such other agreements when needed on favorable terms or at all. The inability to raise capital as and when needed would have a negative impact on the Company’s financial condition and its ability to pursue its business strategy. The Company will need to generate significant revenue to achieve profitability, and it may never do so. Risks and Uncertainties The Company is subject to risks and uncertainties common to early stage companies in the biotechnology industry, including, but not limited to, completing preclinical studies and clinical trials, obtaining regulatory approval for product candidates, market acceptance of products, development by competitors of new technological innovations, dependence on key personnel, the ability to attract and retain qualified employees, reliance on third-party organizations, protection of proprietary technology, compliance with government regulations, and the ability to raise additional capital to fund operations. The Company’s product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure, and extensive compliance-reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Basis of Presentation The accompanying consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiary. Intercompany balances and transactions have been eliminated in consolidation. The accompanying consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). Principles of Consolidation The Company’s consolidated financial statements include the accounts of Prime Medicine, Inc. and its wholly owned subsidiary Prime Medicine Massachusetts Securities Corp., a Massachusetts securities corporation. All significant intercompany balances and transactions have been eliminated in consolidation. Reverse Stock Split On October 12, 2022, in connection with the Company’s initial public offering (“IPO”), the Company effected a 1-3.10880 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios of each series of the Company’s preferred stock. Accordingly, all share and per share amounts for all periods presented in the accompanying condensed consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this stock split and adjustment of the preferred stock conversion ratios.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Actual results may differ materially from those estimates or assumptions. Significant estimates, as determined by the Company, are discussed in greater detail in Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operations . Concentrations of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents, short-term investments, and restricted cash. The Company invests in U.S. Treasury securities and maintains its cash and cash equivalents at high-quality and accredited financial institutions in amounts that could exceed federally insured limits. Cash equivalents are invested in money market funds. However, the Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the time of initial purchase to be cash equivalents. Restricted Cash Restricted cash consists of letters of credit that are required to be maintained in connection with the Company’s lease arrangements. The Company classifies its restricted cash as current or non-current on the consolidated balance sheets based on the expected release dates of the restrictions. Short-term Investments and Related Party Short-Term Investment The Company’s short-term investments consist of investments in U.S. Treasury securities with remaining maturities beyond three months at the date of purchase and one year or less from the balance sheet date. The Company classifies its investments as available-for-sale and carries them at fair market value. The unrealized losses on the Company’s available-for-sale debt securities are recorded in other comprehensive loss in the consolidated statements of operations and comprehensive loss. Short-term debt securities are considered impaired when a decline in fair value is judged to be other-than-temporary. The Company consults with its investment managers and considers available quantitative and qualitative evidence in evaluating potential impairment of its short-term investments on a quarterly basis. If the cost of an individual investment exceeds its fair value, the Company evaluates, among other factors, general market conditions, the duration and extent to which the fair value is less than cost and its intent and ability to hold the investment. Once a decline in fair value is determined to be other-than-temporary, an impairment charge will be recorded to other income (expense), net, in the consolidated statements of operations and comprehensive loss. The Company’s short-term investment — related party was obtained from the collaboration agreement with Beam, which is a public company trading on the Nasdaq Exchange. At each reporting date, the Company recognizes the fair value of the short-term investment — related party on the consolidated balance sheets. Unrealized and realized gains and losses on the Company’s equity investment is included as a component of other income (expense) in the consolidated statements of operations and comprehensive loss. The costs of debt and equity securities for purposes of computing realized and unrealized gains and losses is based on the specific identification method. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or 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. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1 — Quoted prices in active markets for identical assets or liabilities. • Level 2 — Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3 — Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and short-term investments are carried at fair value, determined according to the fair value hierarchy described above. The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Asset Class Estimated Useful Life Laboratory equipment 5 years Furniture and fixtures 5 years Computer hardware and software 3 years Leasehold improvements Shorter of remaining lease term or useful life Costs for capital assets not yet placed into service are capitalized and are depreciated once placed into service. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation and amortization are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance that do not improve or extend the life of the respective assets are charged to expense as incurred. Impairment of Long-Lived Assets Long-lived assets consist primarily of property and equipment, and operating lease right-of-use assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized in loss from operations when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. If such asset group is considered to be impaired, the impairment loss to be recognized is measured based on the excess of the carrying value of the impaired asset group over its fair value. Leases The Company accounts for leases in accordance with ASC 842, Leases . In accordance with ASC 842, the Company determines if an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company classifies leases at the lease commencement date as operating or finance leases and records a right-of-use asset and a lease liability on the consolidated balance sheet for all leases with an initial lease term of greater than 12 months. Leases with an initial term of 12 months or less are not recorded in the balance sheet, but payments are recognized as expense on a straight-line basis over the lease term. The Company has elected not to recognize leases with terms of 12 months or less. A lease qualifies as a finance lease if any of the following criteria are met at the inception of the lease: (i) there is a transfer of ownership of the leased asset to the Company by the end of the lease term, (ii) the Company holds an option to purchase the leased asset that it is reasonably certain to exercise, (iii) the lease term is for a major part of the remaining economic life of the leased asset, (iv) the present value of the sum of lease payments equals or exceeds substantially all of the fair value of the leased asset, or (v) the nature of the leased asset is specialized to the point that it is expected to provide the lessor no alternative use at the end of the lease term. All other leases are recorded as operating leases. The Company enters into contracts that contain both lease and non-lease components. Non-lease components may include maintenance, utilities, and other operating costs. The Company combines the lease and non-lease components of fixed costs in its lease arrangements as a single lease component. Variable costs, such as utilities or maintenance costs, are not included in the measurement of right-of-use assets and lease liabilities, but rather are expensed when the event determining the amount of variable consideration to be paid occurs. Finance and operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease. If the rate implicit is not readily determinable, the Company utilizes an estimate of its incremental borrowing rate based upon the available information at the lease commencement date. Operating lease assets are further adjusted for prepaid or accrued lease payments. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. Certain of the Company’s leases include options to extend or terminate the lease. The amounts determined for the Company’s right-of-use assets and lease liabilities generally do not assume that renewal options or early-termination provisions, if any, are exercised, unless it is reasonably certain that the Company will exercise such options. If initially determined that it is not reasonably certain but subsequently the Company determines that it is reasonably certain to exercise its renewal options or early-termination provisions, the Company would reassess the lease classification, remeasure the lease liability, and adjust the right-of-use asset. In addition to evaluating arrangement that are leases, the Company examines other contracts with suppliers, vendors and outside parties to identify whether such contracts contain an embedded lease and, as applicable, records such embedded leases in accordance with ASC 842. Segment Information The Company operates and manages its business as a single segment for the purposes of assessing performance and making operating decisions. The Company’s chief executive officer, who is the chief operating decision maker, reviews the Company’s financial information on a consolidated basis for purposes of evaluating financial performance and allocating resources. All of the Company’s long-lived assets are located in the United States and all of the Company’s revenue was derived in the United States. Research and Development Expenses Research and development expenses are expensed as incurred. Research and development expenses may consist of costs incurred in connection with acquired in-process research and development and performing research and development activities, including amounts incurred under agreements with external vendors and consultants engaged to perform preclinical studies and to manufacture research and development materials for use in such studies, salaries and related personnel costs, stock-based compensation, consultant fees, and third-party license fees. Upfront payments under license agreements are expensed upon receipt of the license, and annual maintenance fees under license agreements are expensed over the maintenance period. Milestone payments under license agreements are accrued, with a corresponding expense being recognized, in the period in which the milestone is determined to be probable of achievement and the related amount is reasonably estimable. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed. Acquired In-Process Research and Development The Company measures and recognizes asset acquisitions or licenses to intellectual property that are not deemed to be business combinations based on the cost to acquire or license the asset or group of assets, which includes transaction costs. Goodwill is not recognized in asset acquisitions or transaction to license intellectual property. In an asset acquisition or license to intellectual property, the cost allocated to acquire in-process research and development (“IPR&D”) with no alternative future use is recognized as research and development expense on the acquisition date. Upfront and milestone payments made are accrued for and expensed when the achievement of the milestone is probable up to the point of regulatory approval. Milestone payments made upon regulatory approval are capitalized and amortized over the remaining useful life of the related product. Patent Costs The Company expenses all patent-related costs incurred in connection with filing and prosecuting patent applications in the period incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the statements of operations and comprehensive loss. Contingencies The Company is subject to contingent liabilities, such as legal proceedings and claims, that arise in the ordinary course of business activities. The Company accrues for loss contingencies when losses become probable and are reasonably estimable. If the reasonable estimate of the loss is a range and no amount within the range is a better estimate, the minimum amount of the range is recorded as a liability on the consolidated balance sheets. The Company does not accrue for contingent losses that, in its judgment, are considered to be reasonably possible, but not probable; however, it discloses the range of reasonably possible losses. Stock-Based Compensation The Company measures stock-based awards granted to employees, directors and non-employees based on the fair value of the awards on the date of grant using the Black-Scholes option-pricing model. The Black-Scholes option pricing model estimates the fair value of the equity award using the expected term, expected volatility, risk-free interest rate, dividend rate, and the fair value of the common stock underlying the stock-based award. The Company estimates the expected life stock options using the “simplified” method, whereby, the expected life equals the arithmetic average of the vesting term and the original contractual term of the option. Due to the lack of sufficient company-specific historical and implied volatility data, the Company has based its computation of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus. The risk-free interest rates for periods within the expected life of the option were based on the U.S. Treasury yield curve in effect during the period the options were granted. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The Company recognizes forfeitures as they occur. Prior to the IPO, the fair value of common stock underlying stock-based awards was based on an estimate at each grant date by the Company’s board of directors. The Company determined the estimated per share fair value of its common stock at various dates considering contemporaneous and retrospective valuations in accordance with the guidance outlined in the American Institute of Certified Public Accountants Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation. Each of these inputs is subjective and generally requires judgment and estimation by management. Subsequent to the IPO, the fair value of the common stock underlying shared based awards is the quoted market price of the Company’s common stock on the date of the grant. The Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period of the awards for service-based awards, which is generally the vesting period. Stock-based compensation expense is classified in the consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive loss is unrealized gains and losses on marketable securities. Net Loss per Share Attributable to Common Stockholders The Company applies the two-class method when computing net loss per share attributable to common stockholders as the Company has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires loss available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the undistributed earnings as if all loss for the period had been distributed. There is no allocation required under the two-class method during periods of loss since the participating securities do not have a contractual obligation to share in the losses of the Company. The Company has no participating securities outstanding. Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, excluding potentially dilutive common shares and of unvested restricted common stock. Diluted net loss per share attributable to common stockholders is computed by adjusting net loss attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, including potential dilutive common shares. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is generally the same as basic net loss per share attributable to common stockholders since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined based on the differences between the financial statement basis and tax basis of assets and liabilities using enacted tax rates in effect for the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more likely than not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50 percent likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. Recently Issued Accounting Pronouncements Not Yet Adopted From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company will adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and will do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company. As a result of this election, the Company’s financial statements may not be comparable to those public companies that comply with new or revised accounting pronouncements as of public company effective dates. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies. As of December 31, 2023, there are no new accounting pronouncements that are expected to have a material impact on the Company’s financial statements.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The following tables present the Company’s fair value hierarchy for its assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair value: December 31, 2023 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ — $ 24,209 $ — $ 24,209 Short-term investment: U.S. Treasury and government securities — 74,639 — 74,639 Related party short-term investment: Beam equity securities 5,452 — — 5,452 Total cash equivalents and investments $ 5,452 $ 98,848 $ — $ 104,300 December 31, 2022 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ — $ 120,511 $ — $ 120,511 Short-term investment: U.S. Treasury and government securities — 98,467 — 98,467 Related party short-term investment: Beam equity securities 7,834 — — 7,834 Total cash equivalents and investments $ 7,834 $ 218,978 $ — $ 226,812 Money market funds were valued by the Company based on observable inputs, which represent a Level 2 measurement within the fair value hierarchy. The Company classifies its U.S. Treasury securities as short-term based on each instrument’s underlying contractual maturity date. The fair value of the Company’s U.S. Treasury and government securities are classified as Level 2 because they are valued using observable inputs to quoted market prices, benchmark yields, reported trades, broker/dealer quotes or alternative pricing sources with reasonable levels of price transparency and U.S. Treasury securities. Investments in Debt Securities Unrealized gains and losses of investments in debt securities consisted of the following: December 31, 2023 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Short-term investments in debt securities: U.S. Treasury and government securities $ 74,654 $ 7 $ (22) $ 74,639 Total short-term investments in debt securities $ 74,654 $ 7 $ (22) $ 74,639 December 31, 2022 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Short-term investments in debt securities: U.S. Treasury and government securities $ 98,851 $ — $ (384) $ 98,467 Total short-term investments in debt securities: $ 98,851 $ — $ (384) $ 98,467 The contractual maturities of the Company’s investments in debt securities held were as follows: December 31, December 31, Due within one year $ 74,639 $ 98,467 Marketable securities in unrealized loss positions consisted of the following: December 31, 2023 (in thousands, except number of securities) Number of Securities Fair Value Gross Unrealized Losses Investments in continuous loss position for less than 12 months: U.S. Treasury and government securities 11 $ 28,348 $ (22)

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net consisted of the following: December 31, (in thousands) 2023 2022 Property and equipment: Laboratory equipment $ 23,873 $ 19,422 Leasehold improvement 579 564 Furniture and fixture 278 235 Computer hardware and software 11 11 Construction in progress 5,402 1,608 Total property and equipment 30,143 21,840 Less: Accumulated depreciation (7,484) (2,831) Total property and equipment, net $ 22,659 $ 19,009 Depreciation expense related to property and equipment is as follows: Year ended December 31, (in thousands) 2023 2022 Depreciation expense $ 4,653 $ 2,224

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2023
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: December 31, (in thousands) 2023 2022 Accrued expenses and other current liabilities Accrued employee compensation and benefits $ 8,270 $ 6,529 Accrued professional fees 2,273 2,162 Lab-related supplies and services 1,962 1,219 Accrued research and development expense – related party — 329 Other 1,605 449 Total accrued expenses and other current liabilities $ 14,110 $ 10,688

Stockholder_s Equity

Stockholder’s Equity	12 Months Ended
	Dec. 31, 2023
Equity [Abstract]
Stockholder’s Equity	Stockholder’s Equity Reverse Stock Split As described in Note 1, Nature of the Business and Basis of Presentation , in connection with the Company’s IPO in October 2022, the Company effected a 1-for-3.10880 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios of each series of the Company’s preferred stock. Accordingly, all share and per share amounts for all periods presented in the accompanying condensed consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this stock split and adjustment of the preferred stock conversion ratios. Common Stock Under the Third Amended and Restated of Certificate of Incorporation, the Company’s common stock had a par value of $0.0001 and each share of common stock entitles the holder to one vote on all matters submitted to the stockholders for a vote. The holders of common stock are entitled to receive dividends, if any, as declared by the Company’s board of directors. At-The-Market Equity Program In November 2023, the Company entered into Open Market Sale Agreement SM (the “Sales Agreement”) with Jefferies LLC, acting as the Company’s agent and/or principal (the “Sales Agent”), with respect to an “at the market offering” program under which the Company may, from time to time, at its sole discretion, issue and sell shares of its common stock having an aggregate offering price of up to $300.0 million through the Sales Agent. As of December 31, 2023, there have been no sales of common stock pursuant to the Sales Agreement.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation 2019 Equity Incentive Plan The Company’s 2019 Stock Option and Grant Plan (the “2019 Plan”) provides for the Company to grant incentive stock options (“ISO”), non-qualified stock options, unrestricted stock awards, restricted stock awards (“RSA”) and other stock-based awards (collectively, the “Awards”) to the officers, employees, consultants and other key persons of the Company. The 2019 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated. In October 2022, the Company completed its IPO, and in connection with the closing, the board of directors determined that no further awards would be granted under the 2019 Plan. Upon effectiveness of the 2022 Stock Option and Incentive Plan (the “2022 Plan”), shares remaining available for grant under the 2019 Plan were included in the 2022 Plan. Additionally, shares of unused common stock underlying any Awards that are forfeited, canceled or reacquired by the Company prior to vesting will again be available for the grant of awards under the 2022 Plan. 2022 Stock Option and Incentive Plan On February 9, 2022, the Company’s board of directors adopted, and on October 10, 2022 its stockholders approved, the 2022 Plan, which became effective immediately preceding the date on which the registration statement for the Company’s IPO was declared effective by the SEC. The 2022 Plan allows the Company to make equity-based and cash-based incentive awards to its officers, employees, directors, and consultants. The 2022 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted common stock awards, restricted stock units and other stock-based awards. The 2022 Plan provides for an automatic increase in the number of shares reserved and available for issuance on January 1, 2023 and each January 1 thereafter, by five percent of the outstanding number of shares of common stock on the immediately preceding December 31 or such lesser number of shares as determined by the compensation committee. On January 1, 2024, the annual increase for the 2022 Plan resulted in an additional 4,868,856 shares authorized for issuance being added to the 2022 Plan. As of December 31, 2023, the Company had 16,681,302 shares reserved under the 2022 Plan and the 2019 Plan, and 8,627,709 shares available for issuance under the 2022 Plan. 2022 Employee Stock Purchase Plan On February 9, 2022, the Company’s board of directors adopted, and on October 10, 2022 its stockholders approved, the 2022 Employee Stock Purchase Plan (the “2022 ESPP”), which became effective immediately preceding the date on which the registration statement for the Company’s IPO was declared effective by the SEC. The 2022 ESPP provides for an annual increase beginning on January 1, 2023 and each January 1 thereafter through January 1, 2032, by the least of (i) 971,350 shares of common stock, (ii) one percent of the outstanding number of shares of common stock on the immediately preceding December 31, or (iii) such number of shares of common stock as determined by the administrator of the 2022 ESPP. There was no annual increase for the 2022 ESPP on January 1, 2024. As of December 31, 2023, the Company had 1,942,700 shares available for issuance under the 2022 ESPP. No shares of the Company’s common stock were issued during the years ended December 31, 2023 and 2022 under the 2022 ESPP. Stock Option Valuation The following table presents, on a weighted-average basis, the assumptions used in the Black-Scholes option-pricing model to determine the fair value of stock options granted: Year ended December 31, 2023 2022 Risk-free interest rate 3.7 % 3.0 % Expected term (in years) 6.0 6.0 Expected volatility 80.00 % 74.77 % Expected dividend yield — % — % Time-Based Stock Options The following table summarizes the Company’s time-based stock option activity for the year ended December 31, 2023: Number of Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2022 3,954,265 $ 6.43 9.02 $ 48,030 Granted 4,167,494 12.67 Exercised (167,908) 3.91 Forfeited (311,988) 8.76 Outstanding at December 31, 2023 7,641,863 $ 9.79 8.68 $ 12,014 Vested and exercisable at December 31, 2023 2,334,721 $ 7.18 8.19 $ 6,860 Vested and expected to vest at December 31, 2023 7,641,863 $ 9.79 8.68 $ 12,014 Other information related to the time-based stock option activity of the Company was as follows: Year ended December 31, 2023 2022 Weighted-average fair value of options granted $ 8.96 $ 7.40 Intrinsic value of options exercised (in thousands) $ 1,368 $ 681 As of December 31, 2023 there was $40.9 million of total unrecognized compensation cost related to time-based unvested stock options, and the Company expects to recognize such amount over a remaining weighted-average period of 2.7 years. Performance-Based Stock Options The Company has granted stock options to certain employees to purchase shares of common stock that contain certain performance-based vesting criteria related to corporate milestones. The performance-based stock options were granted “at-the-money” and have a term of 10 years. The fair value of each option grant under the performance share option plan was estimated on the date of grant. Recognition of stock-based compensation expense associated with these performance-based stock options commences when the performance condition is considered probable of achievement, using management’s best estimates, which consider the inherent risk and uncertainty regarding the future outcomes of the milestones. The following table summarizes the Company’s performance-based stock option activity for the year ended December 31, 2023: Number of Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2022 411,730 $ 6.65 9.17 $ 4,912 Granted — — Exercised — — Forfeited — — Outstanding at December 31, 2023 411,730 $ 6.65 8.15 $ 1,362 Vested and exercisable at December 31, 2023 121,160 $ 5.11 8.06 $ 454 Other information related to the performance-based stock option activity of the Company was as follows: Year ended December 31, 2023 2022 Weighted-average fair value of options granted $ — $ 9.55 As of December 31, 2023 there was $2.3 million of total unrecognized compensation cost related to performance-based stock options. Restricted Common Stock Awards The Company awarded restricted common stock to employees and non-employees under its 2019 Plan and may continue to award restricted common stock to employees and non-employees under the 2022 Plan. The fair value of each share of restricted common stock is based on the market price of the Company's common stock on the date of grant. The vesting of these restricted stock awards are time-based or performance-based. For a period of up to six months from a grantee’s termination, the Company has the right and option to repurchase unvested restricted common stock at the lower of (i) the original purchase price per share ($0.00004) or (ii) the fair market value per share as of the date of the Company elects to exercise its repurchase right. Time-Based Restricted Common Stocks Awards The majority of the restricted common stock have time-based vesting conditions and vest over a four-year period, subject to the employee’s continued employment with, or service to, the Company on such vesting date. Compensation expense is recognized on a straight-line basis over the vesting period. The following table summarizes the Company’s time-based restricted common stock award activity for the year ended December 31, 2023: Number of Shares Weighted-Average Grant-Date Fair Value Unvested restricted common stock at December 31, 2022 5,015,034 $ 0.10 Issued — — Vested (4,111,807) 0.08 Repurchased — — Unvested restricted common stock at December 31, 2023 903,227 $ 0.17 As of December 31, 2023 , there was $0.2 million of total unrecognized compensation cost related to unvested time-based restricted common stock which the Company expects to recognize over a weighted-average period of 0.7 years. Performance-Based Restricted Common Stock Awards Performance‑based restricted common stock awards vest upon the achievement of performance‑based milestones related to corporate milestones. Stock-based compensation expense associated with the performance-based restricted common stock is recognized if the performance condition is considered probable of achievement using the Company’s best estimates of the time to vesting for the achievement of the performance‑based milestones. Each reporting period, the Company updates its assessment of the probability that the performance-based milestones will be achieved. The fair value of the restricted common stock was based on the fair market value of the Company’s common stock on the date of grant. The following table summarizes the Company’s performance-based restricted common stock award activity for the year ended December 31, 2023: Number of Shares Weighted-Average Grant-Date Fair Value Unvested restricted common stock at December 31, 2022 3,832,769 $ 0.07 Issued — — Vested — — Repurchased — — Unvested restricted common stock at December 31, 2023 3,832,769 $ 0.07 As of December 31, 2023 , there was $0.3 million of total unrecognized compensation cost related to unvested performance-based restricted common stock. Stock-Based Compensation The following table below summarizes the classification of the Company’s stock-based compensation expense related to stock options and restricted common stock awards in the consolidated statements of operations and comprehensive loss: Year ended December 31, (in thousands) 2023 2022 Stock-based compensation expense: Research and development $ 7,950 $ 4,440 General and administrative 5,960 2,019 Total stock-based compensation expense $ 13,910 $ 6,459

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income tax (benefit) expense consists of the following: Year Ended December 31, (in thousands) 2023 2022 Current provision: Federal $ — $ — State — 16 Total current provision — 16 Deferred income tax benefit: Federal 279 314 State — 650 Total deferred income tax benefit 279 964 Total benefit from income taxes $ 279 $ 948 A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2023 2022 Federal income tax expense at statutory rate 21.0 % 21.0 % State income taxes, net of federal benefit 7.3 % 7.7 % Tax credits 2.0 % 2.9 % Permanent differences (0.9) % (0.9) % Other (0.4) % — % Change in valuation allowance (28.9) % (30.0) % Effective income tax rate 0.1 % 0.7 % Net deferred tax assets (liabilities) consisted of the following: December 31, (in thousands) 2023 2022 Deferred tax assets: Capitalized research and development costs $ 49,990 $ 19,974 U.S. and state net operating loss carryforwards 35,977 20,427 Depreciation and amortization 13,204 13,307 Tax credits 12,863 7,268 Accrual 5,817 1,649 Lease Liability 3,711 7,853 Stock Compensation 1,473 122 Other 9 — Total deferred tax assets 123,044 70,600 Deferred tax liabilities: Right of Use Asset (3,794) (8,072) Other — (675) Total deferred tax liabilities (3,794) (8,747) Valuation allowance (119,250) (62,132) Net deferred tax assets (liabilities) $ — $ (279) The following is a summary of the Company’s net operating loss and tax credit carryforwards, both of which may be available to reduce future tax liabilities: December 31, (in thousands) 2023 2022 U.S. federal net operating loss - do not expire $ 131,608 $ 75,202 State net operating loss - expire at various dates beginning in 2039 132,009 73,339 Federal research and development tax credits - expire at various dates beginning in 2040 8,085 4,865 State research and development tax credits - expire at various dates beginning in 2036 6,047 3,042 Utilization of the U.S. federal and state net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Sections 382 and 383 of the Internal Revenue Code of 1986, and corresponding provisions of state law, due to certain ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income and tax liabilities. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50 percent over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before their utilization. Further, until a study is completed by the Company and any limitation is known, no amounts are being presented as an uncertain tax position. The Tax Cuts and Jobs Act requires taxpayers to capitalize and amortize research and development expenditures under section 174 for tax years beginning after December 31, 2021. This rule became effective for the Company for the year ended December 31, 2022. For the years ended December 31, 2023 and 2022, the Company capitalized R&D costs of $137.2 million and $80.7 million, respectively. The Company will amortize these costs for tax purposes over 5 years if the R&D was performed in the U.S. and over 15 years if the R&D was performed outside the U.S. The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception, expectation of future losses and lack of other positive evidence. For the years ended December 31, 2023 and 2022, the Company was in a net deferred tax asset position and therefore recorded a valuation allowance against the portion of its deferred tax assets that cannot be fully supported by the future reversal of existing deferred tax liabilities. The Company has determined that the indefinite nature of the deferred tax liability related to its unrealized gain on its short-term investment — related party can only support 80 percent of the federal deferred tax assets and none of the state deferred tax assets. The Company reevaluates the positive and negative evidence at each reporting period. For the year ended December 31, 2023, the valuation allowance increased primarily due to the increases in net operating loss carryforwards, capitalized research and development costs, and research and development tax credit carryforwards. The changes in the valuation allowance were as follows: Year Ended December 31, (in thousands) 2023 2022 Valuation allowance at beginning of year $ 62,132 $ 25,253 Increases (decreases) recorded to income tax provision 57,118 36,879 Valuation allowance at end of year $ 119,250 $ 62,132 The Company assesses the uncertainty in its income tax positions to determine whether a tax position of the Company is more likely than not to be sustained upon examination, including resolution of any related appeals of litigation processes, based on the technical merits of the position. For tax positions meeting the more-likely-than-not threshold, the tax amount recognized in the financial statements is reduced by the largest benefit that has a greater than 50 percent likelihood of being realized upon the ultimate settlement with the relevant taxing authority. As of December 31, 2023, the Company had not recorded any reserves for uncertain tax positions or related interest and penalties. The Company files income tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. Since the Company is in a loss carryforward position, the Company is generally subject to examination by the U.S. federal, state and local income tax authorities for all years in which a loss carryforward is available. As of December 31, 2023, there were no pending tax examinations. The Company is open to future tax examination under statute from 2019 to the present.

Leases

Leases	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Leases	Leases 21 Erie Street, Cambridge, Massachusetts Lease In March 2020, the Company entered into an operating lease to sublease office and laboratory space located at 21 Erie Street, Cambridge, Massachusetts. This lease was subject to various amendments with the last material amendment entered into in April 2023 for additional office and laboratory space and to extended the term of the sublease through March 2025. The amended lease agreement provides for escalating monthly rental payments with fixed costs for expenses and property taxes included in each payment. Under the terms of the amended lease, the security deposit was increased to $0.7 million, which is classified as other assets on the consolidated balance sheet as of December 31, 2023. In November 2023, the Company exercised its option to terminate this lease with a seven-month notice. This termination was deemed reasonably certain during the year ended December 31,2023, and the Company reassessed the lease and recorded a $6.1 million reduction to the Company’s operating lease liability and its operating lease right-of-use asset on the condensed consolidated balance sheet. 38 Sidney Street, Cambridge, Massachusetts Lease In July 2021, the Company entered into a non-cancelable operating lease to sublease office space in Cambridge, Massachusetts. The lease commenced in August 2021 and expires in December 2024. The Company has a right to extend the lease for one additional six-month period at a market rate as determined by the sublandlord and agreed to by the Company. The option to extend the lease term is not included in the right-of-use asset and lease liability as it is not reasonably certain of being exercised. The lease requires the Company to share in prorated expenses and property taxes based on actual amounts incurred; those amounts are not fixed for future periods and, therefore, are not included in the measurement of the lease. 64 Sidney Street, Cambridge, Massachusetts Lease In July 2021, the Company entered into a non-cancelable operating lease to sublease office space located at 64 Sidney Street, Cambridge, Massachusetts . The lease commenced in April 2022 and will expire in April 2025. The Company has a right to extend the lease for one additional six-month period at a market rate as determined by the sublandlord and agreed to by the Company. The lease requires the Company to share in prorated expenses and property taxes based on actual amounts incurred; t hose amounts are not fixed for future periods and, therefore, these amounts will not be included in the measurement of the lease. 60 First Street, Cambridge, Massachusetts Lease In November 2021, the Company entered into a lease for office and laboratory space in Cambridge, Massachusetts, with rent commencing in March 2024, subject to any credits pursuant to the terms of the lease. Also subject to any credits pursuant to the terms of the lease, the Company expects to pay up to approximately $208.7 million over the initial non-cancelable term of the lease of ten years, and the Company has an option to extend the lease for an additional period of ten years with the rent during the option period being the then fair market rent. The Company secured the lease with a $13.1 million security deposit, which was recorded as restricted cash on the consolidated balance sheets as of December 31, 2023 and December 31, 2022. Under ASC 842, the Company expects that the lease will commence in March 2024. 480 Arsenal Street, Watertown, Massachusetts Lease In May 2022, the Company entered into a non-cancelable operating lease to sublease office space located at 480 Arsenal Street, Watertown, Massachusetts. The lease commenced in May 2022 and will expire in April 2027. The lease requires the Company to share in prorated expenses and property taxes based on actual amounts incurred; those amounts are not fixed for future periods and, therefore, these amounts will not be included in the measurement of the lease. The Company secured the lease with a $0.4 million security deposit, which was recorded as restricted cash on the consolidated balance sheet as of December 31, 2023 and December 31, 2022. In conjunction with the lease, the Company entered into a sublease agreement to sublet a portion of the office space at 480 Arsenal Street Watertown, Massachusetts (the “Arsenal Street Sublease”). The Arsenal Street Sublease commenced in May 2022 and will expire in April 2025. The Company was not relieved of its primary obligation under the operating lease as a result of the sublease. Summary of lease costs recognized The following tables contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the years ended December 31, 2023 and December 31, 2022 . The components of lease cost were as follows: Year Ended December 31, (in thousands) 2023 2022 Lease cost: Operating lease cost $ 13,664 $ 10,999 Variable lease cost 2,145 1,111 Short-term lease cost 2,816 1,401 Sublease income (168) (294) Total lease cost $ 18,457 $ 13,217 The weighted-average remaining lease term and discount rate were as follows: December 31, 2023 2022 Weighted average remaining lease term (in years) 1.9 years 2.7 years Weighted average discount rate 6.92 % 4.92 % Future annual lease payments under non-cancelable operating leases as of December 31, 2023 w ere as follows: (in thousands) Undiscounted Undiscounted lease payments: 2024 $ 9,669 2025 2,656 2026 1,683 2027 567 Total undiscounted lease payments 14,575 Less: imputed interest (942) Total operating lease liability $ 13,633 As the lease for the office and laboratory space at 60 First Street, Cambridge , Massachusetts had not commenced as of December 31, 2023 , the table above excludes any amounts related to this lease. Subject to any credits pursuant to the terms of the lease, the Company expects to pay up to approximately $208.7 million over the initial non-cancelable term of the lease of ten years.

License and Collaboration Agree

License and Collaboration Agreements	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License and Collaboration Agreements	License and Collaboration Agreements For a more detailed discussion of our license and collaboration agreements, please refer to Item 1, Business — Our License and Collaboration Agreements , of this Annual Report on Form 10-K. License Agreements with Broad Institute 2019 License Agreement with Broad Institute In September 2019, the Company entered into a license agreement with Broad Institute, Inc. (“Broad Institute”), and in May 2020, February 2021 and December 2022, the Company entered into amendments to this license agreement, for certain patents related to the field of prevention or treatment of human disease by editing or targeting DNA (the “Broad License Agreement”). Under the Broad License Agreement, Broad Institute granted the Company (i) an exclusive, worldwide license under the licensed patent rights solely to offer for sale, sell, have sold and import products covered by such licensed patent rights, or licensed products, solely for use within the Prime Broad Field (subject to certain specified limitations and exclusions with respect to certain applications), (ii) a non-exclusive, worldwide license under the licensed patent rights solely to make, have made, offer for sale, sell, have sold, and import licensed products solely for use in the Prime Broad Field, (iii) a non-exclusive, worldwide license under the licensed patent rights solely to make, have made, offer for sale, sell, have sold and import other products that are enabled by (a) the licensed patent rights or (b) the use of certain materials transferred to the Company by Broad Institute, solely for the prevention or treatment of human diseases and (iv) a non-exclusive, worldwide license solely for internal research. Further, with respect to DNA delivery or targeting applications covered by the licensed patent rights, the exclusive license granted to the Company by Broad Institute is limited only to “prime editor” products and specifically excludes applications relating to the production or processing of small or large molecules, including for the prevention or treatment of human disease. Under the Broad License Agreement, the Company also has the right to grant sublicenses to its affiliates and third parties, subject to certain requirements. As partial consideration for the license, the Company made a upfront payment of $0.5 million to Broad Institute. Concurrently with the Broad License Agreement, the Company entered into a subscription agreement with Broad Institute (the “Broad Subscription Agreement”), under which the Company issued 623,529 shares of common stock, with a fair value of $39,000. In April 2021, Broad Institute purchased an additional 761,844 shares of Series A preferred stock, at a price of $1.00 per share for gross proceeds of $0.8 million. Under the Broad License Agreement, the Company is obligated to pay Broad Institute an annual license maintenance fee of low six-figures dollar amount beginning in 2022. Broad Institute is also entitled to receive clinical and regulatory milestone payments up to a total of $20.0 million and sales-based milestone payments up to a total of $54.0 million per licensed product. Further, the Broad Institute is entitled to receive mid-single digit percentage royalties, subject to customary offsets and reductions, on net sales of licensed products, and low single-digit percentage royalties of enabled products. Unless earlier terminated, the Broad License Agreement will remain in effect until the later of (i) the last to expire valid claim of an issued patent or pending patent application within the licensed patent rights covering the Company’s licensed products or (ii) the expiration of the last royalty term for a licensed product in a country. The Company can terminate the Broad License Agreement for convenience after a certain period of time following prior written notice to Broad Institute. Each party may terminate the Broad License Agreement for the other party’s uncured material breach within a specified time period following notice of such breach. Broad Institute may also immediately terminate the Broad License Agreement (i) to the extent the Company (or its affiliates or sublicensees) challenges a licensed patent right, (ii) upon the Company’s bankruptcy or insolvency or (iii) if the Company fails to procure and maintain insurance. 2022 License Agreement with Broad Institute In December 2022, the Company entered into a second license agreement with Broad Institute, (the “2022 Broad License Agreement”). Under the 2022 Broad License Agreement, Broad Institute grants to us certain rights and licenses under the patent rights it owns or controls related to MMR inhibition and prime editing improvements and specifically, (i) an exclusive, worldwide license under the licensed patent rights solely to offer for sale, sell, have sold and import products covered by such licensed patent rights, or licensed products, solely for use within the Prime Broad Field (subject to certain specified limitations and exclusions with respect to certain applications), (ii) a non-exclusive, worldwide license under the licensed patent rights solely to make, have made, offer for sale, sell, have sold, and import licensed products solely for use in the Prime Broad Field, (iii) a non-exclusive, worldwide license under the licensed patent rights solely to make, have made, offer for sale, sell, have sold and import other products that are enabled by (a) the licensed patent rights or (b) the use of certain materials transferred to us by Broad Institute, solely for the prevention or treatment of human diseases and (iv) a non-exclusive, worldwide license solely for internal research. Further, with respect to DNA delivery or targeting applications covered by the licensed patent rights, the exclusive license granted to us by Broad Institute is limited only to “prime editor” products and specifically excludes applications relating to the production or processing of small or large molecules, including for the prevention or treatment of human disease. Under the Broad License Agreement, the Company also has the right to grant sublicenses to its affiliates and third parties, subject to certain requirements. The Company is also obligated to pay Broad Institute an annual license maintenance fee of mid five-figures for the term of the Agreement. Broad Institute is also entitled to receive clinical and regulatory milestone payments for a limited category of royalty-bearing products, up to a total of $2.0 million and sales-based milestone payments up to a total of $3.0 million. Further, Broad Institute is entitled to receive royalties of less than 0.2% on net sales of royalty bearing products. Unless earlier terminated, the 2022 Broad License Agreement will remain in effect until the later of (i) the last to expire valid claim of an issued patent or pending patent application within the licensed patent rights covering our licensed products or (ii) the expiration of the last royalty term for a royalty bearing product in a country. The Company can terminate the 2022 Broad License Agreement for convenience following prior written notice to Broad Institute. Each party may terminate the 2022 Broad License Agreement for the other party’s uncured material breach. Broad Institute may also immediately terminate the 2022 Broad License Agreement (i) to the extent we (or our affiliates or sublicensees) challenge a licensed patent right, (ii) upon our bankruptcy or insolvency or (iii) if we fail to procure and maintain insurance. Broad Pledge In February 2021, the Company committed to donate $5.0 million to Broad Institute and Harvard University annually for 14 years, commencing in 2022 (the “Pledge”). The Pledge is intended to be used for research and development related to new genome editing technologies, for example Prime Editing, improve on existing genome-editing technologies, identify delivery mechanisms for these technologies and apply these technologies to the understanding and treatment of rare genetic diseases. The Company can terminate the Pledge at its discretion, subject to providing one year of funding from the date of termination. In August 2022, the Company amended and restated the Pledge to clarify that the funds may be used by the laboratory of David Liu, who is a member of Broad Institute and a faculty member at Harvard. The Company accounts for this Pledge as research and development expenses as it has access to certain data generated as a result of the Pledge. For both the years ended December 31, 2023 and 2022, the Company recognized $5.0 million of research and development expense in connection with the Pledge. Beam Collaboration Agreement — Related Party In September 2019, the Company entered into a collaboration agreement with Beam (the “Beam Collaboration Agreement”) to collaborate on the research, development, manufacture and commercialization of certain Prime Editing products within a specified field and provide each other with access and licenses to certain proprietary technology to advance the other’s progress. Under the Beam Collaboration Agreement, the Company granted Beam an exclusive (even as to the Company and its affiliates), worldwide license under (i) certain Prime Editing technology, know-how and patent rights that the Company controls during the initial term, and improvements thereto that the Company controls for a specified number of years following the initial term, and (ii) the Company’s interest in certain jointly-owned collaboration technology, in each case, solely to develop, make, have made, use, offer for sale, sell, import and commercialize licensed products only in the Beam field. Beam granted to the Company certain non-exclusive, worldwide licenses under certain technology, know-how and patent rights, including under certain CRISPR or delivery-related technology, know-how and patent rights, that it controls during the initial term, and improvements thereto that Beam controls for a specified number of years following the initial term, solely to develop, make, have made, use, offer for sale, sell, import and commercialize products only in the Company’s field. Subject to certain provisions, on a licensed product-by-licensed product basis, we have the right to elect to share equally with Beam in the profits and losses in the United States for Beam’s licensed products. We may exercise such right for each licensed product within a specified period of time. Any such licensed product for which we exercise such right we refer to as a collaboration product. Before and within 30 days after the filing of an IND for a development candidate being developed under the Beam Collaboration Agreement, Beam has the option to designate up to a mid-single digit number of licensed products for which the Company is not permitted to exercise the profit share right (the “Beam Option”). Under the Beam Collaboration Agreement, a licensed product for which the Company has not exercised its profit share option or for which Beam has exercised the Beam Option is collectively referred to as “protected product.” Unless the Company exercises its profit sharing option for a licensed product, Beam is solely responsible for the development and commercialization of licensed products in the Beam field under the Beam Collaboration Agreement. If Beam exercises its option for a protected product, Beam will owe Prime a payment of $5.0 million if the product is developed for non-sickle cell disease or $10.0 million if the product is developed for sickle cell disease. Under the terms of the Beam Collaboration Agreement, the Company is entitled to following milestones: Development milestones Protected product Up to $35.5 million Collaboration product Up to $17.8 million Sales milestones Protected product Up to $84.5 million Collaboration product Up to $42.3 million For eligible products, Beam is obligated to pay the Company tiered royalties, subject to customary offsets and reductions, ranging from a high-single digit percentage to a low double-digit percentage, but less than teens on net sales of protected products worldwide and net sales of collaboration products outside of the United States. In addition, Beam must reimburse the Company for certain payments the Company is required to make to its third-party licensors attributable to Beam’s exercise of any sublicense the Company grants to Beam, including payments it makes to Broad Institute under the Broad License Agreement. If the Company develops a product that is covered by the technology, know-how or patent rights that Beam licenses to the Company under the Beam Collaboration Agreement, which it refers to as a Prime product, the Company is obligated to pay to Beam a low single digit royalty on its worldwide net sales of such any product on a Prime product-by-Prime product and country-by-country basis, subject to certain customary reductions, to a floor. Unless earlier terminated in accordance with its terms, the Beam Collaboration Agreement will expire on the later of (a) expiration of the last royalty term for a product on which a party is obligated to pay royalties to the other party or (b) with respect to any collaboration product, the date on which neither party is developing or commercializing any such collaboration product in the United States. After expiration of the initial term, Beam can terminate the Beam Collaboration Agreement for convenience in its entirety, or on a licensed product-by-licensed product or subfield-by-subfield basis, with prior written notice to the Company. Each party may terminate the Beam Collaboration Agreement for (a) the other party’s uncured material breach, (b) upon the insolvency or bankruptcy of the other party or (c) immediately to the extent the other party (or its affiliates or sublicensees) challenges a patent right licensed to such party. On the first anniversary of the Beam Collaboration Agreement, the Company received 200,307 shares of Beam common stock, with a fair value of $5.5 million and, in return, the Company issued to Beam 1,608,337 shares of the Company’s common stock, with a fair value of $0.2 million. Accounting Considerations The Company concluded that the Beam Collaboration Agreement and the Beam Mutual Subscription Agreement should be combined and treated as a single arrangement for accounting purposes as the agreements were entered into contemporaneously and in contemplation of one another. The Company determined that the combined agreements are accounted for under Topic 606, Revenue recognition. The Company identified the following performance obligations: (i) exclusive, worldwide license to certain Prime patents, (ii) non-exclusive, worldwide licenses to CRISPR technology and (iii) joint research committee participation. The Company also evaluated whether the Beam Option and the Company’s right to elect collaboration products in the Beam Collaboration Agreement represented material rights that would give rise to a performance obligation and concluded that neither the Beam Option nor the Company’s right to elect collaboration products convey a material right to Beam and therefore are not considered separate performance obligations within the Beam Collaboration Agreement. There have been no protected product or collaboration products to date. Under the Beam Collaboration Agreement, the Company is eligible to receive certain milestones and royalties regardless of whether any options are exercised, which are considered variable consideration. At each reporting period, the Company evaluates whether milestones are considered probable of being reached and, to the extent that a significant reversal would not occur in future periods, estimates the amount to be included in the transaction price. During the years ended December 31, 2023 and 2022 the Company did not receive any milestone payments and all variable consideration related to the Beam Collaboration Agreement remained fully constrained. The Company assessed the above promises and determined that the exclusive license for certain Prime products and non-exclusive licenses to CRISPR technology represent performance obligations within the scope of Topic 606. The exclusive license for certain Prime products and non-exclusive licenses to CRISPR technology are considered functional intellectual property and distinct from other promises under the contract. The exclusive license for certain Prime products and non-exclusive licenses to CRISPR technology are considered functional licenses that are distinct in the context of the Beam Collaboration Agreement as Beam can benefit from the licenses on its own or together with other readily available resources. As the exclusive license for certain Prime products and non-exclusive licenses to CRISPR technology are delivered at the same time, they are considered one performance obligation at contract inception. The joint research committee performance promise is immaterial in the context of the contract. The Company determined the transaction price under Topic 606 at the inception of the Beam Collaboration Agreement to be $5.2 million, consisting of the value of the Beam equity investment under the Beam Mutual Subscription Agreement, when measured at fair value, less the value of the Prime shares issued to Beam of $0.2 million. The shares Prime issued to Beam represents a payment to a customer and is therefore a reduction of the transaction price. The Company recognizes revenue for the license performance obligations at a point in time, as control of these licenses are transferred upon issuance and Beam could begin to use and benefit from the licenses. There was no revenue recognized during the years ended December 31, 2023 or 2022. The change fair value of the related party short-term investment consisting of Beam shares are recognized as unrealized gain (loss) i n the consolidated statements of operations and comprehensive loss. Research Collaboration, Option and License Agreement with Myeloid — Related Party In December 2021, the Company and Myeloid, a related party, entered into the Myeloid Agreement. Upon entering into the Myeloid Agreement, Myeloid was entitled to receive an upfront payment of $30.0 million in cash and an aggregate of 1,101,525 shares of the Company’s com mon stock, with a then fair value of $12.0 million, both of which Myeloid received in January 2022. During the second quarter of 2023, the Company provided notice to Myeloid of its intent to terminate the Myeloid Agreement, which became effective during the third quarter of 2023. In September 2023, Myeloid filed an arbitration claim with the American Arbitration Association alleging that the Company breached its obligations under the Myeloid Agreement by failing to pay a $17.5 million milestone payment and seeking, among other things, damages in the amount of $17.5 million. In October 2023, the Company filed an arbitration claim with the American Arbitration Association alleging that Myeloid breached numerous obligations under the Agreement and seeking, among other things, a declaration that Myeloid breached the Agreement, rescission of the Agreement and damages in the amount of $43.5 million. In January 2024, the Company and Myeloid entered into a settlement agreement resolving the two arbitration proceedings. Under the terms of the settlement agreement, the parties agreed to resolve and settle all disputes between the parties and release all claims between them relating to the License Agreement and the arbitrations in exchange for the Company's payment to Myeloid of $13.5 million, certain mutual covenants, and other consideration. Accordingly, for the year ended December 31, 2023, the Company recorded a charge of $13.5 million within its consolidated balance sheets and consolidated statement of operations.

Commitment and Contingencies

Commitment and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company’s commitments under its operating leases are described in Note 9, Leases . License and Collaboration Agreements The Company entered into various license and collaboration agreements under which it is obligated to make fixed and contingent payments as described in Note 10, License and Collaboration Agreements . Legal Proceedings From time to time, the Company may become involved in legal proceedings or other litigation relating to claims arising in the ordinary course of business. The Company accrues a liability for such matters when it is probable that future expenditures will be made and that such expenditures can be reasonably estimated. Significant judgment is required to determine both probability and estimated exposure amount. Legal fees and other costs associated with such proceedings are expensed as incurred. As discussed in Note 10, License and Collaboration Agreements , for the year ended December 31, 2023 the Company recognized $13.5 million under its settlement agreement with Myeloid. As of December 31, 2022, the Company was not a party to any material legal proceedings or claims.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share As described in Note 2, Summary of Significant Accounting Policies , for periods in which the Company reports a net loss, potentially dilutive securities have been excluded from the computation of diluted net loss per share as their effects would be anti-dilutive. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share is the same. The Company excluded the following potential common shares presented based on amounts outstanding at period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: Year Ended December 31, 2023 2022 Anti-dilutive common stock equivalents: Stock options to purchase common stock 7,763,023 4,365,995 Unvested restricted common stock awards 4,735,996 8,847,803 Total anti-dilutive common stock equivalents 12,499,019 13,213,798 Basic and diluted loss per share is computed by dividing net loss by the weighted-average common shares outstanding: Year Ended December 31, (in thousands, except share and per share data) 2023 2022 Numerator: Net loss $ (198,133) $ (121,821) Cumulative dividend on preferred stock — (20,193) Net loss attributable to common stockholders $ (198,133) $ (142,014) Denominator: Weighted-average common shares outstanding, basic and diluted 90,969,327 33,891,264 Net loss per share attributable to common stockholders, basic and diluted $ (2.18) $ (4.19)

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Founder Consulting Services For the years ended December 31, 2023, and 2022 the Company made payments of $0.2 million in each period to one of the co-founder shareholders for scientific consulting and other expenses. As of December 31, 2023 and 2022 , there were no amounts included within accounts payable. Myeloid Therapeutics In December 2021, the Company and Myeloid entered into the Myeloid Collaboration Agreement and Myeloid Subscription Agreement during which time the Company and Myeloid had one common board member, who is also an affiliate of Newpath, one of the Company’s holders of common stock. In 2023, the Company terminated the Myeloid Collaboration Agreement. In January 2024, the Company and Myeloid entered into a settlement agreement resolving two arbitration proceedings, which are described in Note 10, Licenses and Collaboration Agreements . Under the terms of the settlement agreement, the parties agreed to resolve and settle all disputes between the parties and release all claims between them relating to the License Agreement and the arbitrations in exchange for the Company's payment to Myeloid of $13.5 million, certain mutual covenants, and other consideration. The Company recognized the following amounts related to Myeloid: (in thousands) 2023 2022 Expense incurred Settlement $ 13,500 $ — Research and development 560 688 Amounts accrued Settlement 13,500 — Research and development — 329

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Cystic Fibrosis Foundation In January 2024, the Company entered into an agreement with the Cystic Fibrosis Foundation to develop therapies for the treatment of Cystic Fibrosis. Under the term of the agreement, the Company is entitled to received up to $15 million. Funding from the Cystic Fibrosis Foundation will allow Prime Medicine to progress two distinct strategies for applying Prime Editing to treat Cystic Fibrosis. If successful, Cystic Fibrosis Foundation is entitled to receive royalties on net sales. Public Offering In February 2024, the Company issued and sold 22,560,001 shares of its common stock, including 3,360,000 shares pursuant to the exercise of the underwriters’ option to purchase additional shares, at a price to the public of $6.25 per share. Further, in lieu of common stock to certain investors, the Company sold pre-funded warrants to purchase 3,200,005 shares of common stock at a public offering price of $6.24999 per pre-funded warrant, which represents the per share public offering price of each share of common stock less the $0.00001 per share exercise price for each pre-funded warrant. As a result of the offering, the Company received approximately $150.9 million in net proceeds, after deducting underwriting discounts, commissions and estimated offering costs of $10.1 million.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements reflect the operations of the Company and its wholly-owned subsidiary. Intercompany balances and transactions have been eliminated in consolidation. The accompanying consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”).
Principles of Consolidation	Principles of Consolidation The Company’s consolidated financial statements include the accounts of Prime Medicine, Inc. and its wholly owned subsidiary Prime Medicine Massachusetts Securities Corp., a Massachusetts securities corporation. All significant intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting periods. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates, as there are changes in circumstances, facts and experience. Actual results may differ materially from those estimates or assumptions. Significant estimates, as determined by the Company, are discussed in greater detail in Item 7, Management’s Discussion and Analysis of Financial Condition and Results of Operations .
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents, short-term investments, and restricted cash. The Company invests in U.S. Treasury securities and maintains its cash and cash equivalents at high-quality and accredited financial institutions in amounts that could exceed federally insured limits. Cash equivalents are invested in money market funds. However, the Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the time of initial purchase to be cash equivalents.
Short-term Investments and Related Party Short-Term Investment	Short-term Investments and Related Party Short-Term Investment The Company’s short-term investments consist of investments in U.S. Treasury securities with remaining maturities beyond three months at the date of purchase and one year or less from the balance sheet date. The Company classifies its investments as available-for-sale and carries them at fair market value. The unrealized losses on the Company’s available-for-sale debt securities are recorded in other comprehensive loss in the consolidated statements of operations and comprehensive loss. Short-term debt securities are considered impaired when a decline in fair value is judged to be other-than-temporary. The Company consults with its investment managers and considers available quantitative and qualitative evidence in evaluating potential impairment of its short-term investments on a quarterly basis. If the cost of an individual investment exceeds its fair value, the Company evaluates, among other factors, general market conditions, the duration and extent to which the fair value is less than cost and its intent and ability to hold the investment. Once a decline in fair value is determined to be other-than-temporary, an impairment charge will be recorded to other income (expense), net, in the consolidated statements of operations and comprehensive loss.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or 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. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1 — Quoted prices in active markets for identical assets or liabilities. • Level 2 — Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3 — Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Asset Class Estimated Useful Life Laboratory equipment 5 years Furniture and fixtures 5 years Computer hardware and software 3 years Leasehold improvements Shorter of remaining lease term or useful life Costs for capital assets not yet placed into service are capitalized and are depreciated once placed into service. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation and amortization are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance that do not improve or extend the life of the respective assets are charged to expense as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist primarily of property and equipment, and operating lease right-of-use assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized in loss from operations when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. If such asset group is considered to be impaired, the impairment loss to be recognized is measured based on the excess of the carrying value of the impaired asset group over its fair value.
Leases	Leases The Company accounts for leases in accordance with ASC 842, Leases . In accordance with ASC 842, the Company determines if an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company classifies leases at the lease commencement date as operating or finance leases and records a right-of-use asset and a lease liability on the consolidated balance sheet for all leases with an initial lease term of greater than 12 months. Leases with an initial term of 12 months or less are not recorded in the balance sheet, but payments are recognized as expense on a straight-line basis over the lease term. The Company has elected not to recognize leases with terms of 12 months or less. A lease qualifies as a finance lease if any of the following criteria are met at the inception of the lease: (i) there is a transfer of ownership of the leased asset to the Company by the end of the lease term, (ii) the Company holds an option to purchase the leased asset that it is reasonably certain to exercise, (iii) the lease term is for a major part of the remaining economic life of the leased asset, (iv) the present value of the sum of lease payments equals or exceeds substantially all of the fair value of the leased asset, or (v) the nature of the leased asset is specialized to the point that it is expected to provide the lessor no alternative use at the end of the lease term. All other leases are recorded as operating leases. The Company enters into contracts that contain both lease and non-lease components. Non-lease components may include maintenance, utilities, and other operating costs. The Company combines the lease and non-lease components of fixed costs in its lease arrangements as a single lease component. Variable costs, such as utilities or maintenance costs, are not included in the measurement of right-of-use assets and lease liabilities, but rather are expensed when the event determining the amount of variable consideration to be paid occurs. Finance and operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease. If the rate implicit is not readily determinable, the Company utilizes an estimate of its incremental borrowing rate based upon the available information at the lease commencement date. Operating lease assets are further adjusted for prepaid or accrued lease payments. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. Certain of the Company’s leases include options to extend or terminate the lease. The amounts determined for the Company’s right-of-use assets and lease liabilities generally do not assume that renewal options or early-termination provisions, if any, are exercised, unless it is reasonably certain that the Company will exercise such options. If initially determined that it is not reasonably certain but subsequently the Company determines that it is reasonably certain to exercise its renewal options or early-termination provisions, the Company would reassess the lease classification, remeasure the lease liability, and adjust the right-of-use asset. In addition to evaluating arrangement that are leases, the Company examines other contracts with suppliers, vendors and outside parties to identify whether such contracts contain an embedded lease and, as applicable, records such embedded leases in accordance with ASC 842.
Segment Information	Segment Information The Company operates and manages its business as a single segment for the purposes of assessing performance and making operating decisions. The Company’s chief executive officer, who is the chief operating decision maker, reviews the Company’s financial information on a consolidated basis for purposes of evaluating financial performance and allocating resources. All of the Company’s long-lived assets are located in the United States and all of the Company’s revenue was derived in the United States.
Research and Development Expenses	Research and Development Expenses Research and development expenses are expensed as incurred. Research and development expenses may consist of costs incurred in connection with acquired in-process research and development and performing research and development activities, including amounts incurred under agreements with external vendors and consultants engaged to perform preclinical studies and to manufacture research and development materials for use in such studies, salaries and related personnel costs, stock-based compensation, consultant fees, and third-party license fees. Upfront payments under license agreements are expensed upon receipt of the license, and annual maintenance fees under license agreements are expensed over the maintenance period. Milestone payments under license agreements are accrued, with a corresponding expense being recognized, in the period in which the milestone is determined to be probable of achievement and the related amount is reasonably estimable. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed.
Acquired In-Process Research and Development	Acquired In-Process Research and Development The Company measures and recognizes asset acquisitions or licenses to intellectual property that are not deemed to be business combinations based on the cost to acquire or license the asset or group of assets, which includes transaction costs. Goodwill is not recognized in asset acquisitions or transaction to license intellectual property. In an asset acquisition or license to intellectual property, the cost allocated to acquire in-process research and development (“IPR&D”) with no alternative future use is recognized as research and development expense on the acquisition date.
Patent Costs	Patent Costs The Company expenses all patent-related costs incurred in connection with filing and prosecuting patent applications in the period incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the statements of operations and comprehensive loss.
Contingencies	Contingencies The Company is subject to contingent liabilities, such as legal proceedings and claims, that arise in the ordinary course of business activities. The Company accrues for loss contingencies when losses become probable and are reasonably estimable. If the reasonable estimate of the loss is a range and no amount within the range is a better estimate, the minimum amount of the range is recorded as a liability on the consolidated balance sheets. The Company does not accrue for contingent losses that, in its judgment, are considered to be reasonably possible, but not probable; however, it discloses the range of reasonably possible losses.
Stock-Based Compensation	Stock-Based Compensation The Company measures stock-based awards granted to employees, directors and non-employees based on the fair value of the awards on the date of grant using the Black-Scholes option-pricing model. The Black-Scholes option pricing model estimates the fair value of the equity award using the expected term, expected volatility, risk-free interest rate, dividend rate, and the fair value of the common stock underlying the stock-based award. The Company estimates the expected life stock options using the “simplified” method, whereby, the expected life equals the arithmetic average of the vesting term and the original contractual term of the option. Due to the lack of sufficient company-specific historical and implied volatility data, the Company has based its computation of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company, including stage of product development and life science industry focus. The risk-free interest rates for periods within the expected life of the option were based on the U.S. Treasury yield curve in effect during the period the options were granted. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The Company recognizes forfeitures as they occur. Prior to the IPO, the fair value of common stock underlying stock-based awards was based on an estimate at each grant date by the Company’s board of directors. The Company determined the estimated per share fair value of its common stock at various dates considering contemporaneous and retrospective valuations in accordance with the guidance outlined in the American Institute of Certified Public Accountants Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation. Each of these inputs is subjective and generally requires judgment and estimation by management. Subsequent to the IPO, the fair value of the common stock underlying shared based awards is the quoted market price of the Company’s common stock on the date of the grant. The Company recognizes stock-based compensation expense on a straight-line basis over the requisite service period of the awards for service-based awards, which is generally the vesting period. Stock-based compensation expense is classified in the consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive loss is unrealized gains and losses on marketable securities.
Net Loss per Share Attributable to Common Stockholders	Net Loss per Share Attributable to Common Stockholders The Company applies the two-class method when computing net loss per share attributable to common stockholders as the Company has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires loss available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the undistributed earnings as if all loss for the period had been distributed. There is no allocation required under the two-class method during periods of loss since the participating securities do not have a contractual obligation to share in the losses of the Company. The Company has no participating securities outstanding. Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, excluding potentially dilutive common shares and of unvested restricted common stock. Diluted net loss per share attributable to common stockholders is computed by adjusting net loss attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, including potential dilutive common shares. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is generally the same as basic net loss per share attributable to common stockholders since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined based on the differences between the financial statement basis and tax basis of assets and liabilities using enacted tax rates in effect for the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more likely than not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50 percent likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. The Company qualifies as an “emerging growth company” as defined in the Jumpstart Our Business Startups Act of 2012 and has elected not to “opt out” of the extended transition related to complying with new or revised accounting standards, which means that when a standard is issued or revised and it has different application dates for public and nonpublic companies, the Company will adopt the new or revised standard at the time nonpublic companies adopt the new or revised standard and will do so until such time that the Company either (i) irrevocably elects to “opt out” of such extended transition period or (ii) no longer qualifies as an emerging growth company. As a result of this election, the Company’s financial statements may not be comparable to those public companies that comply with new or revised accounting pronouncements as of public company effective dates. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies. As of December 31, 2023, there are no new accounting pronouncements that are expected to have a material impact on the Company’s financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Schedule of Property and Equipment, Net	Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Asset Class Estimated Useful Life Laboratory equipment 5 years Furniture and fixtures 5 years Computer hardware and software 3 years Leasehold improvements Shorter of remaining lease term or useful life Property and equipment, net consisted of the following: December 31, (in thousands) 2023 2022 Property and equipment: Laboratory equipment $ 23,873 $ 19,422 Leasehold improvement 579 564 Furniture and fixture 278 235 Computer hardware and software 11 11 Construction in progress 5,402 1,608 Total property and equipment 30,143 21,840 Less: Accumulated depreciation (7,484) (2,831) Total property and equipment, net $ 22,659 $ 19,009 Depreciation expense related to property and equipment is as follows: Year ended December 31, (in thousands) 2023 2022 Depreciation expense $ 4,653 $ 2,224

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables present the Company’s fair value hierarchy for its assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair value: December 31, 2023 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ — $ 24,209 $ — $ 24,209 Short-term investment: U.S. Treasury and government securities — 74,639 — 74,639 Related party short-term investment: Beam equity securities 5,452 — — 5,452 Total cash equivalents and investments $ 5,452 $ 98,848 $ — $ 104,300 December 31, 2022 (in thousands) Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ — $ 120,511 $ — $ 120,511 Short-term investment: U.S. Treasury and government securities — 98,467 — 98,467 Related party short-term investment: Beam equity securities 7,834 — — 7,834 Total cash equivalents and investments $ 7,834 $ 218,978 $ — $ 226,812
Schedule of Debt and Equity Securities	Unrealized gains and losses of investments in debt securities consisted of the following: December 31, 2023 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Short-term investments in debt securities: U.S. Treasury and government securities $ 74,654 $ 7 $ (22) $ 74,639 Total short-term investments in debt securities $ 74,654 $ 7 $ (22) $ 74,639 December 31, 2022 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Short-term investments in debt securities: U.S. Treasury and government securities $ 98,851 $ — $ (384) $ 98,467 Total short-term investments in debt securities: $ 98,851 $ — $ (384) $ 98,467
Schedule of Investments Classified by Contractual Maturity Date	The contractual maturities of the Company’s investments in debt securities held were as follows: December 31, December 31, Due within one year $ 74,639 $ 98,467
Schedule of Debt Securities, Available-for-Sale	Marketable securities in unrealized loss positions consisted of the following: December 31, 2023 (in thousands, except number of securities) Number of Securities Fair Value Gross Unrealized Losses Investments in continuous loss position for less than 12 months: U.S. Treasury and government securities 11 $ 28,348 $ (22)

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net and Depreciation Expense	Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset as follows: Asset Class Estimated Useful Life Laboratory equipment 5 years Furniture and fixtures 5 years Computer hardware and software 3 years Leasehold improvements Shorter of remaining lease term or useful life Property and equipment, net consisted of the following: December 31, (in thousands) 2023 2022 Property and equipment: Laboratory equipment $ 23,873 $ 19,422 Leasehold improvement 579 564 Furniture and fixture 278 235 Computer hardware and software 11 11 Construction in progress 5,402 1,608 Total property and equipment 30,143 21,840 Less: Accumulated depreciation (7,484) (2,831) Total property and equipment, net $ 22,659 $ 19,009 Depreciation expense related to property and equipment is as follows: Year ended December 31, (in thousands) 2023 2022 Depreciation expense $ 4,653 $ 2,224

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2023
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued expenses and other current liabilities consisted of the following: December 31, (in thousands) 2023 2022 Accrued expenses and other current liabilities Accrued employee compensation and benefits $ 8,270 $ 6,529 Accrued professional fees 2,273 2,162 Lab-related supplies and services 1,962 1,219 Accrued research and development expense – related party — 329 Other 1,605 449 Total accrued expenses and other current liabilities $ 14,110 $ 10,688

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions	The following table presents, on a weighted-average basis, the assumptions used in the Black-Scholes option-pricing model to determine the fair value of stock options granted: Year ended December 31, 2023 2022 Risk-free interest rate 3.7 % 3.0 % Expected term (in years) 6.0 6.0 Expected volatility 80.00 % 74.77 % Expected dividend yield — % — %
Schedule of Share-Based Payment Arrangement, Option, Activity	The following table summarizes the Company’s time-based stock option activity for the year ended December 31, 2023: Number of Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2022 3,954,265 $ 6.43 9.02 $ 48,030 Granted 4,167,494 12.67 Exercised (167,908) 3.91 Forfeited (311,988) 8.76 Outstanding at December 31, 2023 7,641,863 $ 9.79 8.68 $ 12,014 Vested and exercisable at December 31, 2023 2,334,721 $ 7.18 8.19 $ 6,860 Vested and expected to vest at December 31, 2023 7,641,863 $ 9.79 8.68 $ 12,014 Other information related to the time-based stock option activity of the Company was as follows: Year ended December 31, 2023 2022 Weighted-average fair value of options granted $ 8.96 $ 7.40 Intrinsic value of options exercised (in thousands) $ 1,368 $ 681 The following table summarizes the Company’s performance-based stock option activity for the year ended December 31, 2023: Number of Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2022 411,730 $ 6.65 9.17 $ 4,912 Granted — — Exercised — — Forfeited — — Outstanding at December 31, 2023 411,730 $ 6.65 8.15 $ 1,362 Vested and exercisable at December 31, 2023 121,160 $ 5.11 8.06 $ 454 Other information related to the performance-based stock option activity of the Company was as follows: Year ended December 31, 2023 2022 Weighted-average fair value of options granted $ — $ 9.55
Schedule of Share-Based Payment Arrangement, Outstanding Award, Activity, Excluding Option	The following table summarizes the Company’s time-based restricted common stock award activity for the year ended December 31, 2023: Number of Shares Weighted-Average Grant-Date Fair Value Unvested restricted common stock at December 31, 2022 5,015,034 $ 0.10 Issued — — Vested (4,111,807) 0.08 Repurchased — — Unvested restricted common stock at December 31, 2023 903,227 $ 0.17 The following table summarizes the Company’s performance-based restricted common stock award activity for the year ended December 31, 2023: Number of Shares Weighted-Average Grant-Date Fair Value Unvested restricted common stock at December 31, 2022 3,832,769 $ 0.07 Issued — — Vested — — Repurchased — — Unvested restricted common stock at December 31, 2023 3,832,769 $ 0.07
Schedule of Share-Based Payment Arrangement, Expensed and Capitalized, Amount	The following table below summarizes the classification of the Company’s stock-based compensation expense related to stock options and restricted common stock awards in the consolidated statements of operations and comprehensive loss: Year ended December 31, (in thousands) 2023 2022 Stock-based compensation expense: Research and development $ 7,950 $ 4,440 General and administrative 5,960 2,019 Total stock-based compensation expense $ 13,910 $ 6,459

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	Income tax (benefit) expense consists of the following: Year Ended December 31, (in thousands) 2023 2022 Current provision: Federal $ — $ — State — 16 Total current provision — 16 Deferred income tax benefit: Federal 279 314 State — 650 Total deferred income tax benefit 279 964 Total benefit from income taxes $ 279 $ 948
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2023 2022 Federal income tax expense at statutory rate 21.0 % 21.0 % State income taxes, net of federal benefit 7.3 % 7.7 % Tax credits 2.0 % 2.9 % Permanent differences (0.9) % (0.9) % Other (0.4) % — % Change in valuation allowance (28.9) % (30.0) % Effective income tax rate 0.1 % 0.7 %
Schedule of Deferred Tax Assets and Liabilities	Net deferred tax assets (liabilities) consisted of the following: December 31, (in thousands) 2023 2022 Deferred tax assets: Capitalized research and development costs $ 49,990 $ 19,974 U.S. and state net operating loss carryforwards 35,977 20,427 Depreciation and amortization 13,204 13,307 Tax credits 12,863 7,268 Accrual 5,817 1,649 Lease Liability 3,711 7,853 Stock Compensation 1,473 122 Other 9 — Total deferred tax assets 123,044 70,600 Deferred tax liabilities: Right of Use Asset (3,794) (8,072) Other — (675) Total deferred tax liabilities (3,794) (8,747) Valuation allowance (119,250) (62,132) Net deferred tax assets (liabilities) $ — $ (279)
Schedule Of Net Operating Loss And Tax Credit Carryforwards	The following is a summary of the Company’s net operating loss and tax credit carryforwards, both of which may be available to reduce future tax liabilities: December 31, (in thousands) 2023 2022 U.S. federal net operating loss - do not expire $ 131,608 $ 75,202 State net operating loss - expire at various dates beginning in 2039 132,009 73,339 Federal research and development tax credits - expire at various dates beginning in 2040 8,085 4,865 State research and development tax credits - expire at various dates beginning in 2036 6,047 3,042
Summary of Valuation Allowance	For the year ended December 31, 2023, the valuation allowance increased primarily due to the increases in net operating loss carryforwards, capitalized research and development costs, and research and development tax credit carryforwards. The changes in the valuation allowance were as follows: Year Ended December 31, (in thousands) 2023 2022 Valuation allowance at beginning of year $ 62,132 $ 25,253 Increases (decreases) recorded to income tax provision 57,118 36,879 Valuation allowance at end of year $ 119,250 $ 62,132

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Schedule of Lease, Cost	The components of lease cost were as follows: Year Ended December 31, (in thousands) 2023 2022 Lease cost: Operating lease cost $ 13,664 $ 10,999 Variable lease cost 2,145 1,111 Short-term lease cost 2,816 1,401 Sublease income (168) (294) Total lease cost $ 18,457 $ 13,217 The weighted-average remaining lease term and discount rate were as follows: December 31, 2023 2022 Weighted average remaining lease term (in years) 1.9 years 2.7 years Weighted average discount rate 6.92 % 4.92 %
Schedule of Operating Lease Liability	Future annual lease payments under non-cancelable operating leases as of December 31, 2023 w ere as follows: (in thousands) Undiscounted Undiscounted lease payments: 2024 $ 9,669 2025 2,656 2026 1,683 2027 567 Total undiscounted lease payments 14,575 Less: imputed interest (942) Total operating lease liability $ 13,633

License and Collaboration Agr_2

License and Collaboration Agreements (Tables)	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Beam Collaboration Agreement	Under the terms of the Beam Collaboration Agreement, the Company is entitled to following milestones: Development milestones Protected product Up to $35.5 million Collaboration product Up to $17.8 million Sales milestones Protected product Up to $84.5 million Collaboration product Up to $42.3 million

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	Year Ended December 31, 2023 2022 Anti-dilutive common stock equivalents: Stock options to purchase common stock 7,763,023 4,365,995 Unvested restricted common stock awards 4,735,996 8,847,803 Total anti-dilutive common stock equivalents 12,499,019 13,213,798
Schedule of Earnings Per Share, Basic and Diluted	Basic and diluted loss per share is computed by dividing net loss by the weighted-average common shares outstanding: Year Ended December 31, (in thousands, except share and per share data) 2023 2022 Numerator: Net loss $ (198,133) $ (121,821) Cumulative dividend on preferred stock — (20,193) Net loss attributable to common stockholders $ (198,133) $ (142,014) Denominator: Weighted-average common shares outstanding, basic and diluted 90,969,327 33,891,264 Net loss per share attributable to common stockholders, basic and diluted $ (2.18) $ (4.19)

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2023
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	The Company recognized the following amounts related to Myeloid: (in thousands) 2023 2022 Expense incurred Settlement $ 13,500 $ — Research and development 560 688 Amounts accrued Settlement 13,500 — Research and development — 329

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation (Details)	1 Months Ended		12 Months Ended
	Feb. 29, 2024 USD ($) $ / shares shares	Oct. 31, 2022	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Stock issuance costs			$ 0	$ 4,042,000
Accumulated deficit			(491,330,000)	$ (293,197,000)
Cash, cash equivalents, and short-term investments			$ 121,700,000
Reverse stock split		0.32167
Subsequent Event
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Received after discounting	$ 150,900,000
Stock issuance costs	$ 10,100,000
Subsequent Event | Public Offering
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Sale of stock, number of shares issued (in shares) | shares	22,560,001
Sale of stock, price per share (in dollars per share) | $ / shares	$ 6.25
Subsequent Event | Public Offering | Warrant Purchase Agreement Member
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Sale of stock, price per share (in dollars per share) | $ / shares	$ 6.24999
Pre-funded warrants sold (in shares) | shares	3,200,005
Exercise price of warrants (in dollars per share) | $ / shares	$ 0.00001
Subsequent Event | Over-Allotment Option
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Sale of stock, number of shares issued (in shares) | shares	3,360,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Property and Equipment Useful Life (Details)	Dec. 31, 2023
Laboratory equipment
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Furniture and fixture
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Computer hardware and software
Property, Plant and Equipment [Line Items]
Useful life (in years)	3 years

Fair Value Measurements - Hiera

Fair Value Measurements - Hierarchy For Assets and Liabilities Measured At Fair Value On A Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	$ 5,452	$ 7,834
Total assets	104,300	226,812
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	24,209	120,511
U.S. Treasury and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	74,639	98,467
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	5,452	7,834
Total assets	5,452	7,834
Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 1 | U.S. Treasury and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	0	0
Total assets	98,848	218,978
Level 2 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	24,209	120,511
Level 2 | U.S. Treasury and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	74,639	98,467
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related party short-term investment	0	0
Total assets	0	0
Level 3 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Level 3 | U.S. Treasury and government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 0	$ 0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Short-Term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Abstract]
Securities, amortized costs	$ 74,654	$ 98,851
Securities, unrealized gains	7	0
Securities, unrealized losses	(22)	(384)
Securities, fair value	74,639	98,467
U.S. Treasury and government securities
Debt Securities, Available-for-Sale [Abstract]
Amortized Cost	74,654	98,851
Unrealized Gains	7	0
Unrealized Losses	(22)	(384)
Fair Value	$ 74,639	$ 98,467

Fair Value Measurements - Contr

Fair Value Measurements - Contractual Maturities of Short-Term Investments in Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Due within one year	$ 74,639	$ 98,467

Fair Value Measurements and Inv

Fair Value Measurements and Investments - Schedule of Marketable Securities In Unrealized Loss Position (Details) - U.S. Treasury and government securities $ in Thousands	Dec. 31, 2023 USD ($) security
Investments in continuous loss position for less than 12 months:
Number of Securities | security	11
Fair Value	$ 28,348
Gross Unrealized Losses	$ (22)

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 30,143	$ 21,840
Less: Accumulated depreciation	(7,484)	(2,831)
Total property and equipment, net	22,659	19,009
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	23,873	19,422
Leasehold improvement
Property, Plant and Equipment [Line Items]
Total property and equipment	579	564
Furniture and fixture
Property, Plant and Equipment [Line Items]
Total property and equipment	278	235
Computer hardware and software
Property, Plant and Equipment [Line Items]
Total property and equipment	11	11
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 5,402	$ 1,608

Property and Equipment, Net - N

Property and Equipment, Net - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 4,653	$ 2,224

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands		Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued employee compensation and benefits		$ 8,270	$ 6,529
Accrued professional fees		2,273	2,162
Lab-related supplies and services		1,962	1,219
Accrued research and development expense – related party		0	329
Other		1,605	449
Total accrued expenses and other current liabilities	[1]	$ 14,110	$ 10,688
[1] Includes related party amount of $0.3 million as of December 31, 2022.

Stockholder_s Equity (Details)

Stockholder’s Equity (Details) $ / shares in Units, $ in Millions		1 Months Ended
	Oct. 12, 2022	Nov. 30, 2023 USD ($)	Oct. 31, 2022	Dec. 31, 2023 vote $ / shares	Sep. 30, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Reverse stock split			0.32167
Common stock, par value under amendment (in dollars per share) | $ / shares				$ 0.0001
Number of votes per common share | vote				1
Sales Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Offering price | $		$ 300
Common Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Reverse stock split	0.32167
Series A Redeemable Convertible Preferred Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Preferred stock, convertible, conversion ratio					0.1

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($)		12 Months Ended
	Feb. 09, 2022	Dec. 31, 2023	Dec. 31, 2022	Jan. 01, 2024
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation expense		$ 13,910,000	$ 6,459,000
Stock options to purchase common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)		6 years	6 years
Time-Based Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Options outstanding (in shares)		7,641,863	3,954,265
Stock options granted (in shares)		4,167,494
Weighted-average grant-date fair value of stock options granted (in dollars per share)		$ 8.96	$ 7.40
Unrecognized compensation cost		$ 40,900,000
Unrecognized compensation costs, period of recognition (in years)		2 years 8 months 12 days
Performance-Based Stock Options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Options outstanding (in shares)		411,730	411,730
Stock options granted (in shares)		0
Weighted-average grant-date fair value of stock options granted (in dollars per share)		$ 0	$ 9.55
Unrecognized compensation cost		$ 2,300,000
Expected term (in years)		10 years
Unvested restricted common stock awards
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issued (in dollars per share)		$ 0.00004
Restricted Stock, Time-Based
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting period (in years)		4 years
Unrecognized compensation costs, period of recognition (in years)		8 months 12 days
Unrecognized compensation expense		$ 200,000
Restricted Stock, Performance-Based
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized compensation expense		$ 300,000
2022 Stock Option and Incentive Plan and 2019 Equity Incentive Plan | Stock options to purchase common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issuable under plan (in shares)		16,681,302
2022 Stock Option and Incentive Plan | Stock options to purchase common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares remaining available for grant (in shares)		8,627,709
Percentage of annual increase in shares reserved for future issuance	5%
2022 Employee Stock Purchase Plan | Employee Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares remaining available for grant (in shares)		1,942,700
Percentage of annual increase in shares reserved for future issuance	1%
Additional shares allowable under plan (in shares)	971,350
Share-based compensation expense		$ 0	$ 0
2022 Employee Stock Purchase Plan | Employee Stock | Subsequent Event
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares remaining available for grant (in shares)				4,868,856

Stock-Based Compensation - Valu

Stock-Based Compensation - Valuation Assumptions (Details) - Stock Options	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Risk-free interest rate	3.70%	3%
Expected term (in years)	6 years	6 years
Expected volatility	80%	74.77%
Expected dividend yield	0%	0%

Stock-Based Compensation - Time

Stock-Based Compensation - Time-Based Stock Option Activity (Details) - Time-Based Stock Options - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Options
Beginning of period (in shares)	3,954,265
Granted (in shares)	4,167,494
Exercised (in shares)	(167,908)
Forfeited (in shares)	(311,988)
End of period (in shares)	7,641,863	3,954,265
Options vested and exercisable, end of period (in shares)	2,334,721
Options vested and expected to vest, end of period (in shares)	7,641,863
Weighted-Average Exercise Price
Beginning of the period (in dollars per share)	$ 6.43
Granted (in dollars per share)	12.67
Exercised (in dollars per share)	3.91
Forfeited (in dollars per share)	8.76
End of period (in dollars per share)	9.79	$ 6.43
Options vested and exercisable, end of period (in dollars per share)	7.18
Options vested and expected to vest, end of period (in dollars per share)	$ 9.79
Weighted-average remaining contractual term, outstanding (in years)	8 years 8 months 4 days	9 years 7 days
Weighted-average remaining contractual term, vested and exercisable (in years)	8 years 2 months 8 days
Weighted-average remaining contractual term, vested and expected to vest (in years)	8 years 8 months 4 days
Aggregate intrinsic value, outstanding	$ 12,014,000	$ 48,030,000
Aggregate intrinsic value, vested and exercisable	6,860,000
Aggregate intrinsic value, vested and expected to vest	$ 12,014,000
Weighted-average grant-date fair value of stock options granted (in dollars per share)	$ 8.96	$ 7.40
Intrinsic value of options exercised	$ 1,368,000	$ 681,000

Stock-Based Compensation - Perf

Stock-Based Compensation - Performance-Based Stock Option Activity (Details) - Performance-Based Stock Options - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Options
Beginning of period (in shares)	411,730
Granted (in shares)	0
Exercised (in shares)	0
Forfeited (in shares)	0
End of period (in shares)	411,730	411,730
Options vested and exercisable, end of period (in shares)	121,160
Weighted-Average Exercise Price
Beginning of the period (in dollars per share)	$ 6.65
Granted (in dollars per share)	0
Exercised (in dollars per share)	0
Forfeited (in dollars per share)	0
End of period (in dollars per share)	6.65	$ 6.65
Options vested and exercisable, end of period (in dollars per share)	$ 5.11
Weighted-average remaining contractual term, outstanding (in years)	8 years 1 month 24 days	9 years 2 months 1 day
Weighted-average remaining contractual term, vested and exercisable (in years)	8 years 21 days
Aggregate intrinsic value, outstanding	$ 1,362,000	$ 4,912,000
Aggregate intrinsic value, vested and exercisable	$ 454,000

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Activity (Details)	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Restricted Stock, Time-Based
Number of Options
Beginning of period (in shares)	5,015,034
Issued (in shares)	0
Vested (in shares)	(4,111,807)
Repurchased (in shares)	0
End of period (in shares)	903,227
Weighted-Average Exercise Price
Beginning of period (in dollars per share) | $ / shares	$ 0.10
Issued (in dollars per share) | $ / shares	0
Vested (in dollars per share) | $ / shares	0.08
Repurchased (in dollars per share) | $ / shares	0
End of period (in dollars per share) | $ / shares	$ 0.17
Number of awards outstanding (in shares)	903,227
Restricted Stock, Performance-Based
Number of Options
Beginning of period (in shares)	3,832,769
Issued (in shares)	0
Vested (in shares)	0
Repurchased (in shares)	0
End of period (in shares)	3,832,769
Weighted-Average Exercise Price
Beginning of period (in dollars per share) | $ / shares	$ 0.07
Issued (in dollars per share) | $ / shares	0
Vested (in dollars per share) | $ / shares	0
Repurchased (in dollars per share) | $ / shares	0
End of period (in dollars per share) | $ / shares	$ 0.07
Number of awards outstanding (in shares)	3,832,769

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Classification (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 13,910	$ 6,459
Research and development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	7,950	4,440
General and administrative
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 5,960	$ 2,019

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Research and development costs capitalized	$ 137,200,000	$ 80,700,000
Reserves for uncertain tax positions or related interest and penalties	$ 0

Income Taxes - Components of In

Income Taxes - Components of Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Current provision:
Federal	$ 0	$ 0
State	0	16
Total current provision	0	16
Deferred income tax benefit:
Federal	279	314
State	0	650
Total deferred income tax benefit	279	964
Total benefit from income taxes	$ 279	$ 948

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of the Difference Between the Effective Income Tax Rate and the Federal Statutory Rate (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Federal income tax expense at statutory rate	21%	21%
Effective Income Tax Rate Reconciliation, Percent [Abstract]
State income taxes, net of federal benefit	7.30%	7.70%
Tax credits	2%	2.90%
Permanent differences	(0.90%)	(0.90%)
Other	(0.40%)	0%
Change in valuation allowance	(28.90%)	(30.00%)
Effective income tax rate	0.10%	0.70%

Income Taxes - Net Deferred Tax

Income Taxes - Net Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Capitalized research and development costs	$ 49,990	$ 19,974
U.S. and state net operating loss carryforwards	35,977	20,427
Depreciation and amortization	13,204	13,307
Tax credits	12,863	7,268
Accrual	5,817	1,649
Lease Liability	3,711	7,853
Stock Compensation	1,473	122
Other	9	0
Total deferred tax assets	123,044	70,600
Deferred tax liabilities:
Right of Use Asset	(3,794)	(8,072)
Other	0	(675)
Total deferred tax liabilities	(3,794)	(8,747)
Valuation allowance	(119,250)	(62,132)	$ (25,253)
Net deferred tax assets (liabilities)	$ 0	$ (279)

Income Taxes - Schedule Of Net

Income Taxes - Schedule Of Net Operating Loss And Tax Credit Carryforwards (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Line Items]
U.S. federal net operating loss - do not expire	$ 131,608	$ 75,202
State net operating loss - expire at various dates beginning in 2039	132,009	73,339
Domestic Tax Authority
Income Tax Disclosure [Line Items]
Tax credit carryforward	8,085	4,865
State and Local Jurisdiction
Income Tax Disclosure [Line Items]
Tax credit carryforward	$ 6,047	$ 3,042

Income Taxes - Valuation Allowa

Income Taxes - Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Valuation Allowance [Roll Forward]
Valuation allowance at beginning of year	$ 62,132	$ 25,253
Increases (decreases) recorded to income tax provision	57,118	36,879
Valuation allowance at end of year	$ 119,250	$ 62,132

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Nov. 30, 2023 USD ($)	Jul. 31, 2021 tradingDay	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	May 31, 2022 USD ($)	Nov. 30, 2021 USD ($)	Aug. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Termination notice period	7 months
Reduction in operating lease liability	$ 6,100		$ (12,296)	$ (10,248)
Restricted cash			13,496	13,496
Sublease income			168	294
21 Erie Street, Cambridge, Massachusetts Lease
Lessee, Lease, Description [Line Items]
Security deposit							$ 700
38 Sidney Street, Cambridge, Massachusetts Lease
Lessee, Lease, Description [Line Items]
Number of renewal options | tradingDay		1
Operating lease, extension (in years)		6 months
64 Sidney Street, Cambridge, Massachusetts Lease
Lessee, Lease, Description [Line Items]
Number of renewal options | tradingDay		1
Operating lease, extension (in years)		6 months
60 First Street, Cambridge, Massachusetts Lease
Lessee, Lease, Description [Line Items]
Operating lease, extension (in years)						10 years
Expected liability to be paid						$ 208,700
Term of contract, lease not yet commenced (in years)						10 years
Restricted cash			$ 13,100	$ 13,100
480 Arsenal Street, Watertown, Massachusetts Lease
Lessee, Lease, Description [Line Items]
Security deposit					$ 400

Leases - Lease Cost (Details)

Leases - Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Lease, Cost [Abstract]
Operating lease cost	$ 13,664	$ 10,999
Variable lease cost	2,145	1,111
Short-term lease cost	2,816	1,401
Sublease income	(168)	(294)
Total lease cost	$ 18,457	$ 13,217

Leases - Weighted-Average Remai

Leases - Weighted-Average Remaining Lease Term Discount Rate (Details)	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Weighted average remaining lease term (in years)	1 year 10 months 24 days	2 years 8 months 12 days
Weighted average discount rate	6.92%	4.92%

Leases - Schedule of Maturity (

Leases - Schedule of Maturity (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Lessee, Operating Lease, Liability, to be Paid [Abstract]
2024	$ 9,669
2025	2,656
2026	1,683
2027	567
Total undiscounted lease payments	14,575
Less: imputed interest	(942)
Total undiscounted lease payments	$ 13,633

License and Collaboration Agr_3

License and Collaboration Agreements - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands

1 Months Ended

12 Months Ended

Oct. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

Apr. 30, 2021

Feb. 28, 2021

Oct. 31, 2020

Sep. 30, 2020

Sep. 30, 2019

Dec. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

Sep. 30, 2023

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Research and development

[1]

$ 147,905

$ 86,725

Damages value

$ 43,500

Settlement payment — related party

13,500

0

Broad Institute | Collaborative Arrangement, License Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Upfront payment

$ 500

Clinical and regulatory milestone payments, per product

20,000

2,000

Sales-based milestone payments, per product

$ 54,000

3,000

Broad Institute | Collaborative Arrangement, License Agreement | Common Stock

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Stock issued to collaborating party (in shares)

623,529

Fair value of stock issued

$ 39

Broad Institute | Collaborative Arrangement, License Agreement | Series A Redeemable Convertible Preferred Stock

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Sale of stock, number of shares issued (in shares)

761,844

Sale of stock, price per share (in dollars per share)

$ 1

Sale of stock, consideration received

$ 800

Broad Institute | Collaborative Arrangement, 2022 License Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

royalty percentage (in percent)

0.20%

Broad Institute, Inc. and Harvard University | Collaborative Agreement, Pledge

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Pledge commitment

$ 5,000

Pledge commitment term (in years)

14 years

Research and development

5,000

5,000

Beam Therapeutics | Collaborative Arrangement, Related Party

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Profit share option, term to exercise (in days)

30 days

Revenue, remaining performance obligation, variable consideration received

0

0

$ 0

Revenue, remaining performance obligation

$ 5,200

Related party collaboration revenue

$ 0

$ 0

Beam Therapeutics | Collaborative Arrangement, Related Party | Non-Sickle Cell Disease

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Profit share option, amount

5,000

Beam Therapeutics | Collaborative Arrangement, Related Party | Sickle Cell Disease

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Profit share option, amount

$ 10,000

Beam Therapeutics | Collaborative Arrangement, Related Party | Common Stock

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Stock issued to collaborating party (in shares)

200,307

1,608,337

Fair value of stock issued

$ 200

Stock consideration and collaboration revenue

$ 5,500

Myeloid Therapeutics

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Miletone payment default

$ 17,500

Myeloid Therapeutics | Collaborative Arrangement, Option and License Agreement

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Upfront payment

$ 30,000

Myeloid Therapeutics | Collaborative Arrangement, Option and License Agreement | Common Stock

Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]

Stock issued to collaborating party (in shares)

1,101,525

Fair value of stock issued

$ 12,000

[1] Includes related party amounts of $0.6 million and $0.7 million for the years ended December 31, 2023 and 2022, respectively.

License and Collaboration Agr_4

License and Collaboration Agreements - Schedule of Beam Collaboration Agreement (Details) - Beam Therapeutics - Collaborative Arrangement, Related Party $ in Millions	1 Months Ended
	Sep. 30, 2019 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Protected product	$ 35.5
Collaboration product	17.8
Protected product	84.5
Collaboration product	$ 42.3

Commitment and Contingencies (D

Commitment and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Settlement payment — related party	$ 13,500	$ 0

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	12,499,019	13,213,798
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	7,763,023	4,365,995
Unvested restricted common stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities (in shares)	4,735,996	8,847,803

Net Loss per Share - Schedule_2

Net Loss per Share - Schedule of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Numerator:
Net loss	$ (198,133)	$ (121,821)
Cumulative dividend on preferred stock	0	(20,193)
Net loss attributable to common stockholders, basic	(198,133)	(142,014)
Net loss attributable to common stockholders, diluted	$ (198,133)	$ (142,014)
Denominator:
Weighted-average common shares outstanding, diluted (in shares)	90,969,327	33,891,264
Weighted-average common shares outstanding, basic (in shares)	90,969,327	33,891,264
Net loss per share attributable to common stockholders, basic (in dollars per share)	$ (2.18)	$ (4.19)
Net loss per share attributable to common stockholders, diluted (in dollars per share)	$ (2.18)	$ (4.19)

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Settlement payment — related party	$ 13,500	$ 0
Co-Founder Shareholder | Scientific Consulting | Related Party
Related Party Transaction [Line Items]
Amounts of transaction	$ 200	$ 200

Related Party Transactions - Sc

Related Party Transactions - Schedule of Related Party Transactions (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Research and development	[1]	$ 147,905	$ 86,725
Accrued expenses and other current liabilities	[2]	14,110	10,688
Accounts payable		19,537	4,332
Related Party
Related Party Transaction [Line Items]
Accrued expenses and other current liabilities			300
Related Party | Myeloid Therapeutics
Related Party Transaction [Line Items]
Accrued expenses and other current liabilities		13,500	0
Accounts payable		0	329
Related Party | Myeloid Therapeutics | Reimbursement Of Research And Development Expenses
Related Party Transaction [Line Items]
Amounts of transaction		13,500	0
Research and development		$ 560	$ 688
[1] Includes related party amounts of $0.6 million and $0.7 million for the years ended December 31, 2023 and 2022, respectively. Includes related party amount of $0.3 million as of December 31, 2022.

Subsequent Events (Details)

Subsequent Events (Details) - USD ($)	1 Months Ended		12 Months Ended
	Feb. 29, 2024	Jan. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Subsequent Event [Line Items]
Stock issuance costs			$ 0	$ 4,042,000
Subsequent Event
Subsequent Event [Line Items]
Received after discounting	$ 150,900,000
Stock issuance costs	$ 10,100,000
Subsequent Event | Cystic Fibrosis Foundation | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Subsequent Event [Line Items]
Milestone payments		$ 15,000,000
Subsequent Event | Public Offering
Subsequent Event [Line Items]
Sale of stock, number of shares issued (in shares)	22,560,001
Sale of stock, price per share (in dollars per share)	$ 6.25
Subsequent Event | Public Offering | Warrant Purchase Agreement Member
Subsequent Event [Line Items]
Sale of stock, price per share (in dollars per share)	$ 6.24999
Pre-funded warrants sold (in shares)	3,200,005
Exercise price of warrants (in dollars per share)	$ 0.00001
Subsequent Event | Over-Allotment Option
Subsequent Event [Line Items]
Sale of stock, number of shares issued (in shares)	3,360,000