Acelyrin (SLRN) 10-K28 Mar 242023 FY Annual reportFinancial data

Company Profile

Cover

Cover - USD ($) $ in Millions	12 Months Ended
Cover - USD ($) $ in Millions	Dec. 31, 2023	Mar. 25, 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	001-04321
Entity Registrant Name	ACELYRIN, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	85-2406735
Entity Address, Address Line One	4149 Liberty Canyon Road
Entity Address, City or Town	Agoura Hills
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91301
City Area Code	805
Local Phone Number	730-0360
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	SLRN
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	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 1,458.2
Entity Common Stock, Shares Outstanding		98,365,050
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the Annual Meeting of Stockholders, which will be filed with the Securities and Exchange Commission within 120 days after the end of the Registrant’s fiscal year ended December 31, 2023, are incorporated by reference into Part III of this Report.
Entity Central Index Key	0001962918
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false

Audit Information

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

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 218,097,000	$ 267,110,000
Short-term marketable securities	503,229,000	47,510,000
Prepaid expenses and other current assets	15,312,000	1,444,000
Total current assets	736,638,000	316,064,000
Prepaid expenses and other assets, non-current	2,678,000	3,859,000
Operating lease right-of-use asset	1,195,000	0
Property, plant and equipment, net	2,179,000	0
Total assets	742,690,000	319,923,000
Current liabilities
Accounts payable	41,920,000	5,947,000
Accrued research and development expenses	35,436,000	5,717,000
Accrued compensation and other current liabilities	6,833,000	4,237,000
Severance liability	970,000	0
Total current liabilities	85,159,000	15,901,000
Derivative tranche liability	0	10,291,000
Operating lease liability, non-current	1,194,000	0
Total liabilities	86,353,000	26,192,000
Commitments and contingencies (Note 8)
Redeemable convertible preferred shares, no par value; no shares authorized, issued and outstanding as of December 31, 2023; 104,461,636 shares authorized as of December 31, 2022, par value of $0.00001 per share; 40,743,522 shares issued and outstanding as of December 31, 2022; aggregate liquidation preference $408,000 as of December 31, 2022	0	396,593,000
Stockholders’ equity (deficit)
Preferred stock, 10,000,000 shares authorized, $0.00001 par value, no shares issued and outstanding at December 31, 2023; no shares authorized, issued, and outstanding at December 31, 2022
Common stock, par value of $0.00001 per share; 790,000,000 and 229,461,636 shares authorized as of December 31, 2023 and 2022, respectively; 97,865,890 and 2,767,359 shares issued and outstanding as of December 31, 2023 and 2022, respectively	1,000	0
Additional paid-in capital	1,144,893,000	4,302,000
Accumulated other comprehensive income (loss)	162,000	(86,000)
Accumulated deficit	(488,719,000)	(107,078,000)
Total stockholders’ equity (deficit)	656,337,000	(102,862,000)
Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)	$ 742,690,000	$ 319,923,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Redeemable convertible preferred stock, authorized (in shares)	0	104,461,636
Redeemable convertible preferred stock, issued (in shares)	0	40,743,522
Redeemable convertible preferred stock, outstanding (in shares)	0	40,743,522
Redeemable convertible preferred stock, par value (in dollars per share)		$ 0.00001
Redeemable convertible preferred stock, aggregate liquidation preference		$ 408,000
Preferred stock, authorized (in shares)	10,000,000	0
Preferred stock, par value (in dollars per share)	$ 0.00001
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock, authorized (in shares)	790,000,000	229,461,636
Common stock, issued (in shares)	97,865,890	97,865,890
Common stock, outstanding (in shares)	2,767,359	2,767,359

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development	$ 355,886	$ 55,632	$ 38,230
General and administrative	66,178	13,547	3,564
Total operating expenses	422,064	69,179	41,794
Loss from operations	(422,064)	(69,179)	(41,794)
Change in fair value of derivative tranche liability	10,291	487	0
Interest income	30,555	4,052	0
Other expense, net	(423)	(132)	(45)
Net loss	(381,641)	(64,772)	(41,839)
Other comprehensive loss
Unrealized gain (loss) on short-term marketable securities, net	248	(86)	0
Total other comprehensive gain (loss)	248	(86)	0
Net loss and other comprehensive loss	$ (381,393)	$ (64,858)	$ (41,839)
Net loss per share attributable to common stockholder, basic (in shares)	$ (5.43)	$ (41.59)	$ (60.87)
Net loss per share attributable to common stockholder, diluted (in shares)	$ (5.43)	$ (41.59)	$ (60.87)
Weighted-average common shares outstanding, basic (in shares)	70,249,580	1,557,534	687,398
Weighted-average common shares outstanding, diluted (in shares)	70,249,580	1,557,534	687,398

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Total	Series B Convertible Preferred Stock	Series C Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Gain (Loss)
Beginning balance (in shares) at Dec. 31, 2020	4,056,795
Beginning balance at Dec. 31, 2020	$ 7,916
Redeemable Convertible Preferred Stock
Issuance of redeemable convertible preferred stock (in shares)		12,228,923
Issuance of redeemable convertible preferred stock		$ 124,704
Ending balance (in shares) at Dec. 31, 2021	16,285,718
Ending balance at Dec. 31, 2021	$ 132,620
Beginning balance (in shares) at Dec. 31, 2020				2,839,748
Beginning balance at Dec. 31, 2020	(466)			$ 0	$ 1	$ (467)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	233				233
Issuance of common stock upon exercise of options (in shares)				20,284
Issuance of common stock upon exercise of options	16				16
Net loss	(41,839)					(41,839)
Ending balance (in shares) at Dec. 31, 2021				2,860,032
Ending balance at Dec. 31, 2021	$ (42,056)			$ 0	250	(42,306)	0
Redeemable Convertible Preferred Stock
Issuance of redeemable convertible preferred stock (in shares)		12,228,923	12,228,881
Issuance of redeemable convertible preferred stock		$ 124,974	$ 138,999
Ending balance (in shares) at Dec. 31, 2022	40,743,522	24,457,846	12,228,881
Ending balance at Dec. 31, 2022	$ 396,593	$ 249,678	$ 138,999
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock awards (in shares)				498,940
Repurchase and retirement of unvested founders’ common stock (in shares)				(591,613)
Stock-based compensation expense	4,052				4,052
Net loss	(64,772)					(64,772)
Unrealized loss on short-term marketable securities, net	$ (86)						(86)
Ending balance (in shares) at Dec. 31, 2022	2,767,359			2,767,359
Ending balance at Dec. 31, 2022	$ (102,862)			$ 0	4,302	(107,078)	(86)
Redeemable Convertible Preferred Stock
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering (in shares)	(40,743,522)
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering	$ (396,593)
Ending balance (in shares) at Dec. 31, 2023	0
Ending balance at Dec. 31, 2023	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with ValenzaBio acquisition (in shares)				18,885,731
Issuance of common stock in connection with ValenzaBio acquisition (Note 3)	128,735				128,735
Issuance of common stock upon initial public offering, net of underwriting discounts commissions and issuance costs of $47,354 (in shares)				34,500,000
Issuance of common stock upon initial public offering, net of underwriting discounts commissions and issuance costs of $47,354	573,644				573,644
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering (in shares)				40,743,522
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering	396,593			$ 1	396,592
Issuance of common stock upon settlement of restricted stock units, net of shares withheld for taxes (in shares)				303,237
Issuance of common stock upon settlement of restricted stock units, net of shares withheld for taxes	(8,325)				(8,325)
Stock-based compensation expense	$ 47,318				47,318
Issuance of common stock under the employee stock purchase plan (in shares)	24,164			24,164
Issuance of common stock under the employee stock purchase plan	$ 149				149
Issuance of common stock upon exercise of options (in shares)	330,506			641,877
Issuance of common stock upon exercise of options	$ 2,478				2,478
Net loss	(381,641)					(381,641)
Unrealized loss on short-term marketable securities, net	$ 248						248
Ending balance (in shares) at Dec. 31, 2023	2,767,359			97,865,890
Ending balance at Dec. 31, 2023	$ 656,337			$ 1	$ 1,144,893	$ (488,719)	$ 162

Consolidated Statements of Re_2

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Issuance of redeemable convertible preferred stock, derivative liability	$ 10,291
Series B Convertible Preferred Stock
Issuance of redeemable convertible preferred stock, issuance costs	26	$ 296
Series C Convertible Preferred Stock
Issuance of redeemable convertible preferred stock, issuance costs	223
Issuance of redeemable convertible preferred stock, derivative liability	$ 10,778

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net loss	$ (381,641)	$ (64,772)	$ (41,839)
Adjustments to reconcile net loss to net cash used in operations:
Stock-based compensation expense	47,318	4,052	233
Expense related to acquired in-process research and development assets	133,057	0	25,000
Net amortization of premiums and accretion of discounts on short-term marketable securities	(10,495)	(246)	0
Change in fair value of derivative tranche liability	(10,291)	(487)	0
Depreciation and amortization expense	115	0	0
Non-cash lease expense	153	0	0
Changes in assets and liabilities:
Prepaid expense and other current assets	(11,313)	(941)	(49)
Prepaid expenses and other assets, non-current	1,528	(1,964)	0
Accounts payable	34,443	3,776	1,119
Accrued research and development expenses	24,914	(3,980)	9,697
Accrued compensation and other current liabilities	1,691	3,042	860
Operating lease liability	(154)	0	0
Severance liability	970	0	0
Net cash used in operating activities	(169,705)	(61,520)	(4,979)
Cash flows from investing activities
ValenzaBio assets acquisition cash acquired, net of acquisition costs	10,007	0	0
Cash paid to acquire in-process research and development assets	(10,000)	0	(25,000)
Purchase of marketable securities	(956,512)	(175,970)	0
Proceeds from maturities of short-term marketable securities	373,359	128,179	0
Sales of marketable securities	137,696	0	0
Purchase of property, plant and equipment	(2,294)	0	0
Payments for ValenzaBio Acquisition costs	0	(83)	0
Net cash used in investing activities	(447,744)	(47,874)	(25,000)
Cash flows from financing activities
Issuance of common stock upon initial public offering, net of commissions and issuance costs	574,134	0	0
Proceeds from exercise of common stock options and issuance of common stock under the employee stock purchase plan	2,627	0	16
Proceeds from the issuance of redeemable convertible preferred stock, net of issuance costs	0	263,973	124,704
Proceeds allocated to the derivative tranche liability		10,778	0
Payments for deferred offering costs	0	(489)	0
Taxes paid related to net share settlement of restricted stock units	(8,325)	0	0
Net cash provided by financing activities	568,436	274,262	124,720
Net increase (decrease) in cash and cash equivalents	(49,013)	164,868	94,741
Cash and cash equivalents, at beginning of year	267,110	102,242	7,501
Cash and cash equivalents, at end of year	218,097	267,110	102,242
Supplemental disclosure of cash flow information:
Conversion of 40,743,522 redeemable convertible preferred stock upon the closing of initial public offering	396,593	0	0
Common stock issued in connection with ValenzaBio acquisition	128,735	0	0
Right-of-use assets obtained in exchange for operating lease liability	1,348	0	0
Deferred offering costs included in accrued compensation and other current liabilities and accounts payable	0	285	0
ValenzaBio Acquisition costs included in accounts payable	$ 0	$ 1,038	$ 0

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical)	12 Months Ended
Consolidated Statements of Cash Flows (Parenthetical)	Dec. 31, 2023 shares
Common Stock
Conversion of redeemable convertible preferred stock into common stock in connection with initial public offering (in shares)	40,743,522

Description of Business, Organi

Description of Business, Organization and Liquidity	12 Months Ended
Description of Business, Organization and Liquidity	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business, Organization and Liquidity	Description of Business, Organization and Liquidity Organization and Business ACELYRIN, INC. (the “Company”) is a late-stage biopharma company focused on identifying, acquiring, and accelerating the development and commercialization of transformative medicines. The Company was incorporated in the State of Delaware on July 27, 2020. Since its inception, the Company has devoted substantially all of its resources to organizing the Company, hiring personnel, business planning, acquiring and developing its product candidates, performing research and development, enabling manufacturing activities in support of its product development efforts, establishing and protecting its intellectual property portfolio, raising capital, and providing general and administrative support for these activities. The Company did not have any significant operations from the inception date until August 2021. On August 9, 2021, the Company entered into the License and Collaboration Agreement with Affibody AB, a Swedish company, and licensed worldwide development, manufacturing and commercialization rights to a therapeutic candidate, izokibep, for use in the treatment of inflammatory and autoimmune disorders, excluding rights in certain Asian and Nordic countries. See Note 7 for further details. On January 4, 2023, the Company closed the acquisition of ValenzaBio, Inc. (“ValenzaBio”) and issued as consideration 18,885,731 shares of its Class A common stock (“Class A Common Stock”). ValenzaBio was a privately held company developing therapies for autoimmune and inflammatory diseases. The ValenzaBio acquisition added additional assets to the Company’s portfolio, including lonigutamab and SLRN-517. See Note 3 for further details. Reverse Stock Split In April 2023, the Company effected a reverse split of shares of the Company’s outstanding common stock and redeemable convertible preferred stock at a ratio 1.972-for-1 (the “Reverse Stock Split”). The number of authorized shares and par value per share were not adjusted as a result of the Reverse Stock Split. All references to shares, restricted stock units (“RSUs”) and restricted stock awards (“RSAs”), options to purchase common stock, share data, per share data, and related information contained in the consolidated financial statements have been retrospectively adjusted to reflect the effect of the Reverse Stock Split for all periods presented. Initial Public Offering On May 4, 2023, the Company’s Form S-1 Registration Statement for its initial public offering (the “IPO”) was declared effective, and on May 9, 2023, the Company closed its IPO and issued 34,500,000 shares of common stock at a price to the public of $18.00 per share, including 4,500,000 shares issued upon the exercise of underwriters’ option to purchase additional shares of common stock. The Company received gross proceeds of $621.0 million. Net proceeds were approximately $573.6 million, after deducting underwriting discounts and commissions and offering costs of $47.4 million. The common stock began trading on the Nasdaq Global Select Market on May 5, 2023, under the symbol “SLRN”. Immediately prior to the IPO closing, each share of the Company’s redeemable convertible preferred stock then outstanding converted into an equivalent number of shares of Class A Common Stock, and thereafter each share of Class A Common Stock then issued and outstanding was reclassified and became one share of the Company’s common stock. Liquidity The Company has incurred significant losses and negative cash flows from operations since its inception. During the years ended December 31, 2023, 2022 and 2021, the Company incurred net losses of $381.6 million, $64.8 million and $41.8 million, respectively. The net loss of $381.6 million in the year ended December 31, 2023 includes $123.1 million of expenses related to acquired in-process research and development assets without alternative future use and $10.0 million license fee payment to Pierre Fabre incurred in connection with the ValenzaBio acquisition. As of December 31, 2023, the Company had an accumulated deficit of $488.7 million. Cash used in operating activities was $169.7 million, $61.5 million and $5.0 million for the years ended December 31, 2023, 2022 and 2021, respectively. The Company has historically financed its operations primarily through the sale of shares of its redeemable convertible preferred stock in private placements and the sale of shares of its common stock in its IPO. As of December 31, 2023, the Company had cash and cash equivalents and short-term marketable securities of $721.3 million. The Company does not have any products approved for sale and has not generated any revenue from product sales to date. The Company expects to continue to incur significant and increasing expenses and substantial losses for the foreseeable future as it continues its development of and seeks regulatory approvals for its product candidates and commercializes any approved products, seeks to expand its product pipeline and invests in its organization. The Company’s ability to achieve and sustain profitability will depend on its ability to successfully develop, obtain regulatory approval for and commercialize its product candidates. There can be no assurance that the Company will ever earn revenue or achieve profitability, or if achieved, that the revenue or profitability will be sustained on a continuing basis. Unless and until it does, the Company will need to continue to raise additional capital. Management expects that its cash and cash equivalents and short-term marketable securities will be sufficient to fund its current operating plan and capital expenditure requirements for at least the next 12 months from the date of issuance of these consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and include operations of the Company and its wholly owned subsidiary, WH 2 LLC (the legal successor of ValenzaBio). These subsidiaries were formed in contemplation of the Acquisition and did not have any operations and any balances from inception to December 31, 2023. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of expenses during the reporting period. On an ongoing basis, the Company evaluates estimates and assumptions, including but not limited to those related to the fair value of its derivative tranche liability, the fair value of its common stock, stock-based compensation expense, accruals for research and development expenses, fair value of in-process research and development assets acquired, valuation of deferred tax assets, and uncertain income tax positions. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates or assumptions. Segment Information The Company has one operating segment. The Company’s focus is the research, development and commercialization of product candidates. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for allocating and evaluating financial performance. All long-lived assets are maintained in the United States of America. Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. As of December 31, 2023 and 2022, the Company’s cash was deposited in a checking and money market account. Short-Term Marketable Securities Investments with original maturities of greater than 90 days are classified as available-for-sale marketable securities and consist primarily of U.S. Treasury obligations, corporate debt obligations and federal agency obligations. As the Company’s entire investment portfolio is considered available for use in current operations, the Company classifies all investments as available-for-sale and as current assets, even though the stated maturity may be more than one year from the current balance sheet date. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive loss, which is a separate component of stockholders’ equity (deficit) in the consolidated balance sheet. Interest income includes interest, amortization of purchase premiums and discounts, realized gains and losses on sales of securities and other-than-temporary declines in the fair value of investments, if any. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity, which are both recorded to interest income in the Company’s consolidated statement of operations and comprehensive loss. Changes in the fair value of available-for-sale securities impact the consolidated statement of operations and comprehensive loss only when such securities are sold if an allowance for credit losses is recognized or if an impairment is recognized. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. The Company regularly reviews its investment portfolio to determine if any security is impaired, which would require the Company to record an allowance for credit losses or impairment charge in the period any such determination is made. In making this judgment, the Company evaluates, among other things, the duration and extent to which the fair value of a security is less than its cost, its intent to sell or whether it is more likely than not that the Company will be required to sell the security before recovery of its amortized cost basis, the financial condition of the issuer and any changes thereto, and, as necessary, the portion of a decline in fair value that is credit-related. This assessment could change in the future due to new developments or changes in assumptions related to any particular security. Realized gains and losses, allowances for credit losses and impairments on available-for-sale securities, if any, are recorded to interest expense, net in the consolidated statement of operations and comprehensive loss. Fair Value of Financial Instruments Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The carrying amounts of cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other liabilities, approximate fair value due to their short-term maturities. Financial instruments, such as money market funds, short-term marketable securities and derivative tranche liability are measured at fair value at each reporting date (see Note 4). The Company discloses and recognizes the fair value of its assets and liabilities using a hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to valuations based upon unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to valuations based upon unobservable inputs that are significant to the valuation (Level 3 measurements). The guidance establishes three levels of the fair value hierarchy as follows: Level 1 —Observable inputs, such as quoted prices in active markets for identical assets or liabilities. Level 2 —Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and considers factors specific to the asset or liability. The Company recognizes transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs. Concentration of Credit Risk Cash and cash equivalents, and short-term marketable securities are financial instruments that potentially subject the Company to concentrations of credit risk. As of December 31, 2023 and 2022, cash consists of cash deposited with one financial institution and account balances exceed federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial strength of this institution. The Company also has investments in money market funds, U.S. Treasury obligations, corporate debt obligations, and federal agency obligations, which can be subject to certain credit risks. The Company mitigates the risks by investing in high-grade instruments, limiting its exposure to any one issuer and monitoring the ongoing creditworthiness of the financial institutions and issuers. The Company has not experienced any losses on its financial instruments. Risks and Uncertainties The Company is subject to certain risks and uncertainties, including, but not limited to, changes in any of the following areas that the Company believes could have a material adverse effect on the future financial position or results of operations: the timing of, and the Company’s ability to advance its current and future product candidates into and through clinical development; costs and timelines associated with the manufacturing of clinical supplies for the Company’s product candidates; regulatory approval and market acceptance of, and reimbursement for its product candidates; performance of third-party vendors; competition from companies with greater financial resources or expertise; protection of the intellectual property; litigation or claims made by or against the Company based on intellectual property or other factors; compliance with government regulations; and its ability to attract and retain employees necessary to support its growth. The Company has expended and will continue to expend substantial funds to complete the research, development and clinical testing of its product candidates. The Company also will be required to expend additional funds to establish commercial-scale manufacturing arrangements and to provide for the marketing and distribution of products that receive regulatory approval. If any of its product candidates are approved, the Company will require additional funds to commercialize its products. The Company is unable to entirely fund these efforts with its current financial resources. If adequate funds are unavailable on a timely basis from additional sources of financing, the Company may have to delay, reduce the scope of or eliminate one or more of its research or development programs, which would materially and adversely affect its business, financial condition and operations. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty of the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the consolidated statements of operations and comprehensive loss. Asset Acquisitions and Acquired In-Process Research and Development Expenses The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the asset or group of assets, which includes transaction costs. The Company determined that ValenzaBio acquisition should be accounted for as an asset acquisition after considering whether substantially all of the fair value of the gross assets acquired was concentrated in a single asset or group of assets and whether the Company acquired a substantive process capable of significantly contributing to the Company’s ability to create outputs. The fair value of in-process research and development assets is determined based on the present value of future discounted cash flows. Contingent consideration in asset acquisitions payable in the form of cash is recognized in the period the triggering event is determined to be probable of occurrence and the related amount is reasonably estimable. Such amounts are expensed or capitalized based on the nature of the associated asset at the date the related contingency is resolved. Redeemable Convertible Preferred Stock The Company records shares of redeemable convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The redeemable convertible preferred stock is recorded outside of permanent equity because while it is not mandatory, redemption is contingent upon the occurrence of certain events considered not solely within the Company’s control. The Company has not adjusted the carrying values of the redeemable convertible preferred stock to the liquidation preferences of such shares because a deemed liquidation event obligating the Company to pay the liquidation preferences to holders of shares of redeemable convertible preferred stock is not probable of occurring. Subsequent adjustments to the carrying values to the liquidation preferences will be made only when it becomes probable that such a deemed liquidation event will occur. Following the Company's IPO that was closed on May 9, 2023, all redeemable convertible preferred stock shares were converted to the Company's common stock shares. Derivative Tranche Liability In connection with the initial closing of the Series C preferred stock financing in September 2022, the Company had a commitment and Series C investors had an obligation to purchase the Series C Second Tranche at a fixed price, if specified conditions were met on June 30, 2023. The obligation to issue additional shares of Series C redeemable convertible preferred stock at a future date was determined to be a freestanding derivative instrument and was accounted for as a liability. The derivative tranche liability was accounted for at fair value at the issuance date and remeasured at the end of each reporting period until the shares are issued or the obligation expires. Changes in the fair value of the derivative tranche liability are recognized in the consolidated statement of operations and comprehensive loss. Research and Development Expenses and Accrued Liabilities Research and development costs are expensed as incurred. Research and development costs include salaries, stock-based compensation, and benefits for employees performing research and development activities, expenses incurred under agreements with consultants, third parties’ organizations and vendors that conduct clinical studies, other supplies and costs associated with product development efforts, preclinical activities, and regulatory operations. Payments associated with licensing agreements to acquire exclusive licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternate future use are also expensed as incurred. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and recorded in prepaid expenses and other current assets, and then expensed as the related goods are delivered or the services are performed. The Company records accrued liabilities for estimated costs of its research and development activities conducted by third-party service providers. The Company accrues these costs based on factors such as estimates of the work completed and in accordance with the third-party service agreements. If the Company does not identify costs that have begun to be incurred or if the Company underestimates or overestimates the level of services performed or the costs of these services, actual expenses could differ from the estimates. To date, the Company has not experienced any material differences between accrued costs and actual costs incurred. The Company makes payments in connection with clinical trials to contract manufacturing organizations (“CMOs”) that manufacture the material for its product candidates and to clinical research organizations (“CROs”) and clinical trial sites that conduct and manage the Company’s clinical trials. The financial terms of these contracts are subject to negotiation, which vary by contract and may result in payments that do not match the periods over which materials or services are provided. Generally, these agreements set forth the scope of work to be performed at a fixed fee, unit price or on a time and materials basis. In the event the Company makes advance payments for goods or services that will be used or rendered for future research and development activities, the payments are deferred and capitalized as a prepaid expense and recognized as expense as the goods are received or the related services are rendered. These payments are evaluated for current or long-term classification based on when they are expected to be realized. Stock-Based Compensation Expense The Company grants stock-based equity awards including restricted stock awards, restricted stock units, performance-based restricted stock units, and stock options to employees and members of its board of directors (the “Board”). These awards are accounted at fair value on the award grant date. Stock-based compensation expense is recognized over the awards’ vesting period on a straight-line basis and recorded as either research and development or general and administrative expenses in the statements of operations and comprehensive loss based on the function to which the related services are provided. Forfeitures are accounted for as they occur. Performance-based restricted stock units (“PSUs”), awarded to employees vest upon the achievement of certain performance milestones and market conditions (i.e., specified average stock price hurdle) at the end of specified performance periods, subject to continuous service through each respective vest date. The amount of expense recognized is based on the grant date fair value of the PSU tranche corresponding to the performance condition of the tranche which is considered probable. The estimated grant date fair value of the market portion of the PSUs is based on a Monte Carlo simulation under each performance condition outcome. The Monte Carlo valuation model simulates the probabilities of stock price achievement, which requires management to make a number of assumptions including a 20-trading day volume-weighted average stock price, volatility of our peers, and the risk-free interest rate. Compensation expense for each tranche of a PSU award is recognized straight-line over the period commencing on the grant date of the award and ending on the vesting date of the tranche under the PSU award. Cumulative adjustments are recorded at each reporting date to reflect subsequent changes to the estimated outcome of the performance condition until the end of the respective performance period. The Company uses the Black-Scholes option pricing model to determine the fair value of stock options and restricted stock awards if these are similar to early exercised options. The use of the Black-Scholes option pricing model requires the Company to make assumptions with respect to the fair value of the Company’s common stock at grant date, expected term of the option, the expected volatility of the common stock consistent with the expected life of the option, risk-free interest rates and expected dividend yields of the common stock. The Company estimates the fair value of restricted stock units based on the fair value of the Company’s common stock at a grant date. Stock-based compensation expense related to stock options granted to non-employees is recognized based on the fair value of the stock options, determined using the Black-Scholes option pricing model. The awards generally vest over the time period the Company expects to receive service from the non-employee. Foreign Currency Transactions Transactions denominated in foreign currencies are initially measured in U.S. dollars using the exchange rate on the date of the transaction. Foreign currency denominated monetary assets and liabilities are subsequently remeasured at the end of each reporting period using the exchange rate at that date, with the corresponding foreign currency transaction gain or loss recorded in the statements of operations and comprehensive loss. Income Taxes The Company accounts for income taxes using the asset and liability method. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. In evaluating the ability to recover deferred income tax assets, the Company considers all available positive and negative evidence, including operating results, ongoing tax planning and forecasts of future taxable income on a jurisdiction-by-jurisdiction basis. In the event the Company determines that it would be able to realize deferred income tax assets in the future in excess of their net recorded amount, the Company would make an adjustment to the valuation allowance that would reduce the provision for income taxes. Conversely, in the event that all or part of the net deferred tax assets are determined not to be realizable in the future, an adjustment to the valuation allowance would be charged to earnings in the period when such determination is made. As of December 31, 2023 and 2022, the Company had recorded a full valuation allowance on deferred tax assets. Tax benefits related to uncertain tax positions are recognized when it is more likely than not that a tax position will be sustained during an audit. The tax benefit recognized is measured as the largest amount of benefit which is more likely than not to be realized upon settlement with the taxing authority. Changes in recognition or measurement are reflected in the period in which the change in judgement occurs. Interest and penalties related to unrecognized tax benefits are included within the provision for income tax. Net Loss Per Share Attributable to Common Stockholders Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period, without consideration of potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock and potentially dilutive securities outstanding for the period. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. The Company’s other comprehensive income (loss) is comprised solely of unrealized gains (losses) on available-for-sale marketable securities. The Company has not recorded any reclassifications from other comprehensive income (loss) to net loss during the period presented. Leases The Company adopted ASU 2016-02, “Leases (Topic 842)” accounting standard as of January 1, 2022. The contractual arrangements that meet the definition of a lease are classified as operating or finance leases and are recorded on the balance sheets as both a right-of-use asset (“ROU asset”) and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company’s incremental borrowing rate (“IBR”). Lease ROU assets and lease obligations are recognized based on the present value of the future minimum lease payments over the lease term at the lease commencement date. The Company currently does not have any finance leases. Operating lease ROU assets are adjusted for (i) payments made at or before the commencement date, (ii) initial direct costs incurred, and (iii) tenant incentives under the lease. As the implicit rate for the operating leases are not determinable, the Company determines its IBR based on the information available at the applicable lease commencement date. The IBR is determined by using the rate of interest that the Company would pay to borrow on a collateralized basis an amount equal to the lease payments for a similar term and in a similar economic environment where the asset is located. The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably certain the Company will exercise any option to extend the contract. Lease costs for minimum lease payments for operating leases are recognized on a straight-line basis over the lease term. Lease liabilities are increased by interest and reduced by payments each period, and the ROU asset is amortized over the lease term. Variable lease costs are recorded when incurred. In measuring the ROU assets and lease liabilities, the Company has elected to combine lease and non-lease components. The Company excludes short-term leases, if any, having initial terms of 12 months or less at lease commencement as an accounting policy election, and recognizes rent expense on a straight-line basis over the lease term for these types of leases. The Company did not have any leases as of and prior to January 1, 2023. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (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, as amended (the “JOBS Act”), 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. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies. In November 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which requires all public entities, including public entities with a single reportable segment, to provide in interim and annual periods one or more measures of segment profit or loss used by the chief operating decision maker to allocate resources and assess performance. In addition, this guidance requires disclosures of significant segment expenses and other segment items as well as incremental qualitative disclosures. This guidance is effective for fiscal years beginning after December 15, 2023, and interim periods after December 15, 2024, with retrospective application required, and early adoption permitted. The Company is currently in the process of evaluating the effects of this guidance on its related disclosures. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which requires enhanced income tax disclosures, including specific categories and disaggregation of information in the effective tax rate reconciliation, disaggregated information related to income taxes paid, income or loss from continuing operations before income tax expense or benefit, and income tax expense or benefit from continuing operations. This guidance is effective for annual periods beginning after December 15, 2024, with early adoption permitted. The Company is currently in the process of evaluating the impact of this pronouncement on its related disclosures.

ValenzaBio Acquisition

ValenzaBio Acquisition	12 Months Ended
ValenzaBio Acquisition	Dec. 31, 2023
Business Combination and Asset Acquisition [Abstract]
ValenzaBio Acquisition	ValenzaBio Acquisition On December 20, 2022, the Company entered into the Agreement and the Plan of Merger and Reorganization (the “Merger Agreement”) to acquire ValenzaBio. In connection with the planned ValenzaBio acquisition, the Company formed two wholly owned subsidiaries, WH1, Inc. and WH2 LLC in November 2022. Through the two-step merger and restructuring, WH1 Inc. was merged with and into ValenzaBio with WH1 Inc. ceasing to exist, and ValenzaBio was then merged with and into WH2 LLC, with WH2 LLC continuing as the legal successor to ValenzaBio. (the “Acquisition”). The Acquisition closed on January 4, 2023 (the “Closing Date”). The Company concluded that the Acquisition is an asset acquisition as substantially all of the fair value of the gross assets acquired, excluding cash, was concentrated in a single asset, lonigutamab, and the Company did not acquire a workforce or any substantive process capable of significantly contributing to the ability to create outputs. As consideration, the Company issued 18,885,731 shares of its Class A Common Stock to ValenzaBio stockholders, of which 2,013,673 were being held by Seller LLC for any post-acquisition costs and general indemnities for 12 months from the Closing Date ("Holdback Release Date"), and paid $7,663 in cash to one non-accredited investor. Additionally, $0.1 million is payable in cash to Seller LLC to cover Seller LLC’s fees and expenses related to the Acquisition, with any unused amount to be released to ValenzaBio stockholders as soon as practicable following the completion of Seller LLC’s responsibilities. The Company also incurred $1.2 million of acquisition-related costs that were included in the total consideration and capitalized to assets acquired. The Company assumed options of certain ValenzaBio option holders who entered into consulting agreements with the Company, which became options for the purchase of an aggregate of 1,249,811 shares of the Company’s Class A Common Stock upon the closing of the Acquisition on January 4, 2023. The assumed options vested in full on March 31, 2023. Each assumed option is exercisable until the earlier of (i) 12 months following the termination of the option holder’s continuous service with the Company, or (ii) the original expiration date of such assumed option. Outstanding ValenzaBio shares were exchanged into shares of the Company's Class A Common Stock and the options described above assumed at an exchange ratio of 0.8027010-for-one. The following table represents the total purchase consideration (in thousands): Issued Class A Common Stock (1) $ 128,735 Transaction costs (2) 1,271 Cash (3) 8 Total $ 130,014 (1) Shares were issued for consideration at $6.86 per share, including 2,013,673 shares that were being held by Seller LLC until the Holdback Release Date. The Company used a third party valuation specialist to assist management in determining the fair value of the shares of Class A Common Stock at the Closing Date. (2) Legal and advisory transaction costs of $1.3 million incurred by the Company in connection with the Acquisition, including $0.1 million payable in cash to Seller LLC for the expense fund. (3) Cash payment of $7,663 to one non-accredited investor for settlement of vested ValenzaBio options. The following is the allocation of the purchase consideration to the acquired assets and liabilities (in thousands): Cash $ 11,369 Prepaid expenses and other current assets 2,074 In-process research and development assets 123,057 Accounts payable (1,628) Accrued research and development expenses (4,805) Accrued compensation and other current liabilities (53) Total net asset acquired $ 130,014 In-process research and development (“IPR&D) assets were related to acquired product candidates: lonigutamab in clinical trials and SLRN-517 in preclinical development. The fair value of in-process research and development assets was based on the present value of future discounted cash flows, which was based on significant estimates. These estimates included the number of potential patients and market prices of future product candidates, costs required to conduct clinical trials, future milestones and royalties payable under acquired license agreements, costs to receive regulatory approval and potentially commercialize product candidates, as well as estimates for probability of success and the discount rate. The estimated fair values of lonigutamab and SLRN-517 assets were $114.8 million and $8.2 million, respectively. The Company concluded that acquired assets do not have an alternative future use and recognized the full amount of $123.1 million as research and development expenses in the consolidated statement of operations and comprehensive loss in January 2023. There are a number of additional obligations under the Merger Agreement that are separate from the assets and liabilities acquired, including the following: Assumed options. The assumed options, discussed above, did not have substantive service requirement, and were accounted as a separate transaction from the Acquisition. The fair values of assumed options of $3.1 million and $1.8 million was expensed as research and development and general and administrative expenses, respectively, in the consolidated statement of operations and comprehensive loss for the year ended December 31, 2023. Settled equity awards . In accordance with the severance obligations of ValenzaBio and per the terms of the Merger Agreement, certain unvested options and restricted stock awards of former ValenzaBio employees, who did not enter into consulting agreements with the Company, were accelerated and net exercised upon the closing of the Acquisition and termination of employment of such ValenzaBio employees. The fair value of unvested equity awards of $0.9 million was expensed as general and administrative expense in the consolidated statement of operations and comprehensive loss for the year ended December 31, 2023. Payments in cash to one non-accredited investor for settlement of unvested ValenzaBio options and one former ValenzaBio employee to whom options were promised but not granted at the Closing Date of $8,387 and $30,000, respectively, were expensed as general and administrative expenses in the consolidated statement of operations and comprehensive loss for the year ended December 31, 2023. Severance payment obligation. In accordance with the severance plan of ValenzaBio, the Company is obligated to make severance payments to certain former ValenzaBio employees of approximately $5.1 million, including estimated taxes, for a period of three As of December 31, 2023, severance payments obligations to ValenzaBio employees in the amount of $0.3 million were included in the consolidated balance sheet. The accretion of severance payments obligations of $0.1 million were included in each of research and development and general and administrative expenses, respectively, in the consolidated statement of operations and comprehensive loss for the year ended December 31, 2023. Amendment to Pierre Fabre Agreement.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
Fair Value Measurements	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company’s financial instruments measured at fair value on a recurring basis consist of Level 1, Level 2, and Level 3 financial instruments. Usually, short-term marketable securities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. Corporate debt obligations, commercial paper, government agency obligations and asset-backed securities are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. Financial assets and liabilities are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies, or similar techniques, and at least one significant model assumption or input is unobservable. The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): Fair Value Measurements as of December 31, 2023 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash and cash equivalents) $ 23,205 $ 23,205 $ — $ — U.S. Treasury obligations ($146,497 included in cash and cash equivalents) 525,353 — 525,353 — Corporate debt obligations ($23,313 included in cash and cash equivalents) 135,284 — 135,284 — Federal agency obligations ($15,344 included in cash and cash equivalents) 27,746 — 27,746 — Total fair value of assets $ 711,588 $ 23,205 $ 688,383 $ — Fair Value Measurements as of December 31, 2022 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash and cash equivalents) $ 238,223 $ 238,223 $ — $ — U.S. Government bonds 25,459 — 25,459 — U.S. Treasury bills 11,404 11,404 — — Corporate debt obligations 2,141 — 2,141 — Federal agency obligations 8,506 — 8,506 — Total fair value of assets $ 285,733 $ 249,627 $ 36,106 $ — Liabilities: Derivative tranche liability $ 10,291 $ — $ — $ 10,291 Total fair value of liabilities $ 10,291 $ — $ — $ 10,291 Classified as: December 31, 2023 December 31, 2022 Cash and cash equivalents $ 208,359 $ 238,223 Short-term marketable securities 503,229 47,510 Total cash equivalents and marketable securities $ 711,588 $ 285,733 The following table sets forth the changes in the fair value of Level 3 liabilities (in thousands): Derivative Tranche Liability 2023 2022 Balance as of January 1st $ 10,291 $ — Fair value of derivative tranche liability upon issuance — 10,778 Change in fair value (10,291) (487) Balance as of December 31st $ — $ 10,291 The derivative tranche liability The following significant assumptions were used to estimate fair value of the derivative tranche liability as of December 31, 2022: Probability of achieving specified conditions 80 % Fair value of Series C preferred stock share $ 12.2661 Discount rate 25 %

Available-For-Sale Marketable S

Available-For-Sale Marketable Securities	12 Months Ended
Available-For-Sale Marketable Securities	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Available-For-Sale Marketable Securities	Available-For-Sale Marketable Securities The following tables summarize the estimated fair value of the Company’s available-for-sale marketable securities as of December 31, 2023 and 2022 (in thousands): As of December 31, 2023 Total Total Unrealized Gain Total Total Money market funds (included in cash and cash equivalents) $ 23,205 $ — $ — $ 23,205 U.S. Treasury obligations ($146,497 included in cash and cash equivalents) 525,198 156 (1) 525,353 Corporate debt obligations ($23,313 included in cash and cash equivalents) 135,288 36 (40) 135,284 Federal agency obligations ($15,344 included in cash and cash equivalents) 27,735 12 (1) 27,746 Total available for sale marketable securities $ 711,426 $ 204 $ (42) $ 711,588 As of December 31, 2022 Total Total Unrealized Loss (1) Total Money market funds (included in cash and cash equivalents) $ 238,223 $ — $ 238,223 U.S. Government bonds 25,506 (47) 25,459 U.S. Treasury obligations 11,430 (26) 11,404 Corporate debt obligations 2,145 (4) 2,141 Federal agency obligations 8,515 (9) 8,506 Total available for sale marketable securities $ 285,819 $ (86) $ 285,733 ______________ (1) The Company did not have any gross unrealized gains as of December 31, 2022. As of December 31, 2023 and 2022, no significant facts or circumstances were present to indicate a deterioration in the creditworthiness of the issuers of the marketable securities, and the Company has no requirement or intention to sell these securities before maturity or recovery of their amortized cost basis. The Company considered the current and expected future economic and market conditions and determined that its investments were not significantly impacted. For all securities with a fair value less than its amortized cost basis, the Company determined the decline in fair value below amortized cost basis to be immaterial and non-credit related, and therefore no allowance for losses has been recorded. During the years ended December 31, 2023, 2022, and 2021, the Company did not recognize any impairment losses on its investments. The Company presents accrued interest receivable related to the available-for-sale marketable securities in prepaid expenses and other current assets As of December 31, 2023, all available-for-sale marketable securities mature within one year.

Consolidated Balance Sheet Comp

Consolidated Balance Sheet Components	12 Months Ended
Consolidated Balance Sheet Components	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidated Balance Sheet Components	Consolidated Balance Sheet Components Prepaid expenses and other current assets Prepaid expenses and other current assets consist of the following (in thousands): As of December 31, 2023 2022 Prepaid research and development expenses $ 8,184 $ 682 Value-Added Tax (VAT) receivable 3,985 — Prepaid insurance and other current assets 1,712 86 Interest receivable 764 138 Prepaid other services 667 288 Research and development credit receivable — 250 $ 15,312 $ 1,444 Prepaid expenses and other assets, non-current Other non-current assets consist of the following (in thousands): As of December 31, 2023 2022 Prepaid research and development expenses, non-current $ 2,644 $ 1,964 Security deposits 34 — Acquisition transaction costs — 1,121 Deferred IPO offering costs — 774 $ 2,678 $ 3,859 Property, plant and equipment, net Property, plant and equipment consisted of the following as of December 31, 2023 (in thousands) : December 31, 2023 Construction in progress $ 1,460 Computer and other equipment 407 Furniture and fixtures 306 Leasehold improvements 121 Total property, plant and equipment, gross 2,294 Less: accumulated depreciation and amortization (115) Property, plant and equipment, net $ 2,179 There was no property, plant and equipment balance as of December 31, 2022. Accrued research and development expenses Accrued research and development expenses are comprised of the following (in thousands): As of December 31, 2023 2022 Accrued clinical manufacturing expenses $ 22,232 $ 1,292 Accrued clinical expenses 13,204 4,425 $ 35,436 $ 5,717 Accrued compensation and other current liabilities Accrued compensation and other current liabilities are comprised of the following (in thousands): As of December 31, 2023 2022 Accrued compensation $ 5,417 $ 3,068 Accrued professional services fees (1) 1,099 808 Other accrued expenses and current liabilities 317 361 $ 6,833 $ 4,237 (1) IPO offering costs included in accrued liabilities were zero and $0.2 million as of December 31, 2023 and December 31, 2022, respectively.

Significant Agreements

Significant Agreements	12 Months Ended
Significant Agreements	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Significant Agreements	Significant Agreements Affibody License and Collaboration Agreement On August 9, 2021, the Company entered into a license agreement with Affibody AB (“Affibody”) (the “Affibody Agreement”) under which Affibody granted the Company exclusive, sublicensable licenses to develop, commercialize and manufacture products containing izokibep for all human therapeutic uses on a worldwide basis, subject to a pre-existing agreement with Inmagene Biopharmaceuticals (“Inmagene”) with respect to certain Asian countries. The Company chairs a global joint steering committee composed of designees from Affibody, Inmagene and the Company and retains final decision-making authority for izokibep global development. In doing so, the Company is obligated to use commercially reasonable efforts (i) to develop products containing izokibep worldwide, excluding certain defined territories, (ii) for the conduct and finalization of certain ongoing clinical trials, and (iii) to commercialize products containing izokibep for all human therapeutic uses worldwide, excluding certain defined territories, after obtaining the applicable marketing authorization. The Company is responsible for manufacturing both the clinical and commercial supply of licensed product globally. In connection with the Affibody Agreement, the Company paid a non-refundable upfront license fee in the aggregate amount of $3.0 million in August 2021 and September 2021, and $22.0 million in October 2021. The Company is also obligated to pay Affibody (i) an aggregate of up to $280.0 million, $30.0 million of which would be due prior to the first approval in the United States, upon the achievement of various development, regulatory and commercialization milestones and (ii) high single-digit to low-teens royalties on net sales of licensed products in the territory where the Company has commercialization rights, subject to certain reductions. Royalties will be due on a licensed product-by-licensed product and country-by-country basis beginning after the first commercial sale of the licensed product, except in Mainland China, Hong Kong, Macau, Taiwan and South Korea, and lasting until the later of (a) the expiration of all valid patent claims or regulatory exclusivity covering the licensed product in that country and (b) ten years after such first commercial sale. In the event the FDA grants the Company (or its affiliates or sublicensees) a priority review voucher for a licensed product, the Company will pay Affibody either: (a) if the Company sells or transfer such priority review voucher to a third-party, approximately one third of the proceeds received from the sale, net of taxes, or (b) if the Company uses the priority review voucher for an indication or product outside the scope of the Affibody Agreement, approximately one third of the fair market value of the priority review voucher as determined in accordance with the Affibody Agreement. Unless earlier terminated, the Affibody Agreement will continue on a licensed product-by-licensed product basis and country-by-country basis until there are no more royalty payments owed to Affibody on any licensed product thereunder. The acquisition of the exclusive license was accounted for as an in-process research and development asset acquisition and as the acquired technology did not have an alternative use, the total consideration of $25.0 million was recorded as research and development expense in the consolidated statements of operations and comprehensive loss for the year ended December 31, 2021. Milestone payments are contingent consideration and are accrued when contingent events occur and achievement of milestones is probable. In November 2023, the Company paid a total amount of $15.0 million in relation with attaining one of the development milestones described above and recorded the payment within research and development expenses in the consolidated statement of operations and comprehensive loss for the year ended December 31, 2023. Royalties will be recognized as cost of sales when products are sold and royalties are payable. No other milestone or royalties were probable and estimable as of December 31, 2023 and 2022. Pierre Fabre License and Commercialization Agreement Upon the closing of the Acquisition, the Company became the successor to ValenzaBio’s rights under the March 25, 2021 license and commercialization agreement between ValenzaBio and Pierre Fabre, as amended (the “Pierre Fabre Agreement”). The Company received certain exclusive worldwide licenses, with the right to sublicense, to certain patents, know-how and other intellectual property to develop, manufacture, use and commercialize lonigutamab for non-oncology therapeutic indications. The license from Pierre Fabre extends to any product containing lonigutamab (excluding any fragments or derivatives) as its sole active ingredient (each, a “PF Licensed Product”). The Pierre Fabre Agreement prohibits the Company from using the licensed intellectual property in any antibody drug conjugate, multi-specific antibodies or any other derivatives of lonigutamab. In the event the Company decides to sublicense the rights to develop or commercialize a PF Licensed Product in any territory outside of the United States and Canada, Pierre Fabre retains the right of first negotiation to acquire such development and commercialization rights in one or more countries in such territory. Subject to the validation of certain clinical trial criteria by a joint steering committee, Pierre Fabre has the option to reclaim all exclusive rights to develop, commercialize and exploit the PF Licensed Product in such territories and to obtain an exclusive sublicensable license in such territories for any improvements and trademarks to such PF Licensed Product, and to exploit such PF Licensed Product for non-oncology therapeutic indications, subject to certain payment obligations. If Pierre Fabre exercises such option, and intends to sublicense such rights, then the Company has the right of first negotiation to acquire such development and commercialization rights as to that territory, or Pierre Fabre has the right to require the Company to buy out its right to the option for a one-time payment of $31.0 million or the Company has the right to choose to buy out Pierre Fabre’s option by making the one-time payment of $31.0 million within 30 days from Pierre Fabre’s notice of exercise of such option. If Pierre Fabre does not exercise its option within the option period or if the Company buys out Pierre Fabre’s right to the option, the option will expire or terminate, respectively. The Company is solely responsible for the development, regulatory approvals and commercialization of each PF Licensed Product except to the extent that Pierre Fabre reclaims rights to a PF Licensed Product in the option territory. As consideration for the amendment to the Pierre Fabre Agreement, which became effective upon the closing of the Acquisition (see Note 3), the Company paid Pierre Fabre an aggregate license payment of $10.0 million. The Company is also obligated to (i) make payments of up to $99.5 million upon the achievement of various development and regulatory milestones, (ii) make milestone payments of up to $390.0 million upon the achievement of certain commercial milestones, and (iii) pay tiered royalties in the high single-digit to low-teen percentages to Pierre Fabre on worldwide net sales in a given calendar year. Royalties will be payable for each PF Licensed Product in a given country during a period commencing upon the first commercial sale of such PF Licensed Product in such country and continuing until the latest of (a) 10 years after such first commercial sale, (b) expiration of last-to-expire valid claim in a licensed patent in such country and (c) expiration of regulatory exclusivity for such PF Licensed Product in such country. In the event the Company enters into a sublicense with a third party, the Company must also share with Pierre Fabre a percentage of any revenues from option fees, upfront payments, license maintenance fees, milestone payments or the like generated from the sublicense. Such percentage may be between the high single-digits to the low thirties based on which stage of development of a PF Licensed Product the sublicense relates to. Unless earlier terminated, the Pierre Fabre Agreement will continue on a PF Licensed Product-by-PF Licensed Product and country-by-country basis until there are no more royalty payments owed to Pierre Fabre on any PF Licensed Product thereunder. Either party may terminate the Pierre Fabre Agreement upon an uncured material breach, or upon the bankruptcy or insolvency of the other party. Pierre Fabre may also terminate the agreement if the Company or any of its affiliates institutes a patent challenge against the licensed patents from Pierre Fabre. The Company may also terminate the Pierre Fabre Agreement with or without cause upon nine months’ prior written notice, so long as there is no ongoing clinical trial for any PF Licensed Product. As of December 31, 2023, no milestones were probable and accrued in the consolidated balance sheet. The payment of $10.0 million for additional license fees was recorded as research and development expenses in the consolidated statement of operations and comprehensive loss for the year ended December 31, 2023. Novelty Nobility License and Commercialization Agreement Upon the closing of the Acquisition, the Company became the successor to an exclusive license agreement between ValenzaBio and Novelty Nobility (the “Novelty License Agreement”) and obtained a worldwide exclusive license for the development and commercialization of SLRN-517, an unmodified IgG1 monoclonal antibody, as a therapeutic treatment. In connection with the arrangement, the Company is obligated to (i) make development and regulatory milestones of up to $44.3 million, (ii) make commercial sales milestone payments of up to $682.0 million and (iii) pay tiered royalties of a low single-digit to high-single-digit percentage on future worldwide net sales. The Novelty License Agreement is effective on a licensed product-by-licensed product and country-by-country basis until the expiration of the latest to expire royalty term, unless early terminated. The royalty term, with respect to a licensed product and a country is the period commencing on the first commercial sale of such product in such country, and ending upon the latest to occur of: a) there being no patent right in such country that had at least one valid claim covering the licensed product in whole or in part, or the manufacture or use thereof; b) 10 years from the first commercial sale of such product worldwide; or c) expiration of regulatory exclusivity for such product in such country. The agreement can be early terminated upon (i) a material breach, (ii) abandonment of development by the Company, in which the Company ceases all development activities for the licensed product, (iii) termination by patent challenge, and (iv) insolvency. The Company may terminate the contract at any point, upon 30 days prior written notice to Novelty Nobility, Inc. As of December 31, 2023, no milestones were probable and accrued in the consolidated balance sheet.

Commitments and Contingent Liab

Commitments and Contingent Liabilities	12 Months Ended
Commitments and Contingent Liabilities	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities	Commitments and Contingent Liabilities License Agreement The Company is required to pay certain milestones upon the achievement of specific development and regulatory events, upon products’ commercialization and products’ royalties under its license agreements, including its agreements with Affibody, Pierre Fabre, Novelty Nobility and other non-exclusive license agreements. None of the milestones, other than the $15.0 million Afiibody milestone disclosed in Note 7, were achieved or probable, all products were in development, as such, no milestones or royalties were accrued in the condensed consolidated balance sheets as of December 31, 2023 and 2022. Research and Development Agreements The Company enters into various agreements in the ordinary course of business, such as those with suppliers, contract research organizations, contract manufacturing organizations, and clinical trial sites. These contracts generally provide for termination on notice or may have a potential termination fee if a purchase order is canceled within a specified time. The total value of non-cancellable obligations under contracts was $142.3 million and $0.1 million as of December 31, 2023 and 2022, respectively. This presentation of non-cancellable purchase obligations does not include any estimates of potential reduction of such liabilities related to mitigation obligations of the counter-parties in the event of cancellation under the terms of our engagements. During both fiscal years there were no amounts accrued related to termination and cancellation charges in the consolidated balance sheets, as the Company has not determined cancellation to be probable. Non-cancelable purchase obligations for services to be performed or product to be manufactured, as of December 31, 2023 amount to: 2024 67,567 2025 53,686 2026 20,985 2027 and thereafter 106 Total $ 142,344 Lease In January 2023, the Company entered into a lease agreement to rent approximately 10,012 square feet of office space in Agoura Hills, California. The term of the lease is 65 months with an option to extend it for an additional three years. Monthly rent payments are approximately $30,500, subject to an annual 3.0% increase and six months rental abatement during the first year. In addition to the base rent, the Company is obligated to pay variable costs related to its share of operating expenses and taxes. In connection with the lease agreement, the Company made a security deposit $34,000 that is included in prepaid expenses and other assets, non-current in the consolidated balance sheet as of December 31, 2023. As of the lease commencement date the Company recorded $1.3 million as right-of-use (“ROU”) asset and operating lease liability, non-current, in the consolidated balance sheet. In July 2023, the Company entered into a lease agreement to rent approximately 22,365 square feet of office space in South San Francisco with the commencement date to be determined upon completion of work to be performed by the landlord. The term of the lease is 60 months with an option to extend it for an additional three years at then current market rates. Monthly base rent payments are approximately $150,000, subject to an annual 3.5% increase and a share of building operating expenses. The lease has not commenced as of December 31, 2023. Operating lease costs were $0.3 million for the year ended December 31, 2023, and were recorded in general and administrative expenses and research and development expenses in the consolidated statements of operations and comprehensive loss. During the year ended December 31, 2023, the Company recognized a total of $0.1 million in expense related to short-term leases recorded as general administrative expense in the consolidated statements of operations and comprehensive loss. The following table summarizes a maturity analysis of the Company’s operating lease liabilities showing the aggregate lease payments as of December 31, 2023 (in thousands): 2024 375 2025 386 2026 398 2027 409 2028 280 Total future lease payments 1,848 Less imputed interest (434) Total operating lease liability balance 1,414 Less current portion of lease liability (included in accrued compensation and other current liabilities) (220) Operating lease liability, non-current $ 1,194 The weighted-average remaining lease term was 56 months and the weighted-average discount rate was 12%. Cash paid for amounts included in the measurement of lease liabilities was less than $0.1 million. Legal Contingencies On November 15, 2023, a purported federal securities class action lawsuit was commenced in the United States District Court for the Central District of California. An amended complaint was filed on March 26, 2024 (Boukadoum v. Acelyrin, Inc. et al., No. 2:23-cv-09672-FMO-MAA), naming us and current and former executive officers and directors as defendants. The complaint alleges that the defendants violated the Exchange Act and Securities Act by misleading investors about the Phase 2b trial of izokibep in HS. The original complaint was filed following our announcement of the week 16 results from the Part B portion of such Phase 2b trial. The complaint seeks damages and an award of reasonable costs and expenses, including attorneys' fees, expert fees and other costs, as well as such other and further relief as the court may deem just and proper. It is possible that additional suits will be filed, or allegations made by stockholders, with respect to these same or other matters and also naming the Company and/or its officers and directors as defendants. This lawsuit and any other potential lawsuits are subject to inherent uncertainties, and the actual defense and disposition costs will depend upon many unknown factors. The outcome of this lawsuit is necessarily uncertain. The Company could be forced to expend significant resources in the defense against this and any other related lawsuits and the Company may not prevail. The Company currently is not able to estimate the possible loss to the Company from this lawsuit, as this lawsuit is currently at an early stage, and such amounts could be material to the Company’s financial statements even if the Company prevails in the defense against this lawsuit. The Company cannot be certain how long it may take to resolve this lawsuit or the possible amount of any damages that the Company may be required to pay. The Company does not consider any payment to be probable or reasonably estimable and has not accrued for any potential liability relating to this lawsuit. From time to time, the Company may become involved in additional legal proceedings or be subject to claims arising in the ordinary course of business. The Company records a liability for such matters when it is probable that future losses will be incurred and that such losses can be reasonably estimated. Significant judgment is required to determine both probability and the estimated amount. Guarantees and Indemnifications In the normal course of business, the Company enters into agreements that contain a variety of representations and provide for general indemnification. Its exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To the extent permitted under Delaware law, the Company has agreed to indemnify its directors and officers for certain events or occurrences while the director or officer is, or was serving, at a request in such capacity. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. As of December 31, 2023, the Company did not have any material indemnification claims that were probable or reasonably possible and consequently has not recorded related liabilities.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	12 Months Ended
Redeemable Convertible Preferred Stock	Dec. 31, 2023
Temporary Equity [Abstract]
Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock In October 2021, the Company entered into a Series B stock purchase agreement and issued 12,228,923 shares of its Series B redeemable convertible preferred stock (the “Series B Stock”) at a price of $10.2217 per share for aggregate gross cash proceeds of $125.0 million, and incurred issuance costs of $0.3 million. The Company also agreed to issue and the investors also agreed to purchase additional 12,228,923 shares of the Series B Stock at the same price per share within 15 days of the earliest to occur: (i) January 30, 2022; (ii) the Company filing a Form S-1 with the Securities and Exchange Commission; or (iii) a date determined by the majority of the Board when the Company has a critical need for additional capital (the “Series B Second Tranche”). The Company closed the Series B Second Tranche and received $125.0 million in aggregate gross proceeds in February 2022. The obligation to issue and purchase shares was concluded to be a tranche right liability. The fair value of the liability was estimated to be de minimis at the issuance date and at the closing date, as the expected term was three months, and there were no significant changes in the estimated fair value of the Series B Stock at the Series B Second Tranche closing date. In February 2022, the Company closed the Series B Second Tranche financing and issued 12,228,923 shares of Series B redeemable convertible preferred stock (the "Series B Stock") at a price of $10.2217 per share for gross cash proceeds of $125.0 million and incurred less than $0.1 million issuance costs. In September 2022, the Company entered into a Series C stock purchase agreement and issued 12,228,881 shares of Series C redeemable convertible preferred stock (the “Series C Stock”) at a price of $12.2661 per share for gross cash proceeds of $150.0 million (the “Series C First Tranche Closing”) and incurred issuance costs of $0.2 million. Pursuant to the Series C preferred stock purchase agreement, the Company and investors agreed to issue and purchase an additional 12,228,881 shares of Series C Stock at the same purchase price of $12.2661 per share on June 30, 2023, subject to meeting certain conditions (the “Series C Second Tranche Closing”) (see Note 10). If a Series C Stock holder did not purchase the full number of the Series C Second Tranche shares that was required to be purchased by it on the Series C Second Tranche Closing date and this holder became a defaulting purchaser, then each 10 shares of Series C Stock held by such holder would have automatically converted into one share of Class A Common Stock, as adjusted for any stock dividends, splits, recapitalizations and the like in accordance with the Company’s then-current certificate of incorporation. On May 9, 2023, the IPO closing date, each share of the Company’s redeemable convertible preferred stock then issued and outstanding automatically converted into one share of the Company’s Class A Common Stock, thereafter each share of Class A Common Stock then issued and outstanding was reclassified and became one share of common stock and the Series C Second Tranche Closing was terminated. The authorized, issued, and outstanding shares of the Company’s convertible preferred stock and liquidation preferences as of December 31, 2022 were as follows (in thousands, except for share amounts): December 31, 2022 Shares Shares Issued Aggregate Net Series A redeemable convertible preferred stock 8,000,000 4,056,795 $ 8,000 $ 7,916 Series B redeemable convertible preferred stock 48,230,900 24,457,846 250,000 249,678 Series C redeemable convertible preferred stock 48,230,736 12,228,881 150,000 138,999 Total redeemable convertible preferred stock 104,461,636 40,743,522 $ 408,000 $ 396,593 The significant rights, preferences and privileges of the Company’s redeemable convertible preferred stock were as follows: Dividends — The holders of Series A Stock, Series B Stock and Series C Stock were entitled to receive noncumulative dividends at the rate of 8% of the original issue price per share, when, as and if declared by the Board. No dividends were declared and payable for the years ended December 31, 2023, 2022, and 2021. Liquidation Rights — In the event of the liquidation, dissolution, or winding up of the Company, or a deemed liquidation event, including a merger or consolidation, or a sale or other disposition of all or substantially all of the Company’s assets, the holders of shares of Series C Stock and Series B Stock were entitled to receive, before any payments were made to the holders of Series A Stock or common stock, an amount per share equal to the greater of: (i) Series C Stock and the Series B Stock original issuance price of $12.2661 and $10.2217, respectively, plus any dividends declared but unpaid; or (ii) such amount per share as would have been payable had all shares of Series C Stock and Series B Stock been converted into common stock immediately prior to such liquidation, dissolution, winding up or deemed liquidation. Should the Company’s legally available assets be insufficient to satisfy the Series C Stock and Series B Stock liquidation preference, the funds were to be distributed with equal priority and pro rata among the holders of the Series C Stock and Series B Stock in proportion to the preferential amount each holder was otherwise entitled to receive. After full payment to holders of the Series C Stock and Series B Stock, a payment would be made to the holders of Series A Stock, in preference to the holders of the common stock, in an amount per share equal to the greater of: (i) the Series A Stock original issuance price of $1.9720, plus any dividends declared but unpaid; or (ii) such amount per share as would have been payable had all shares of Series A Stock been converted into common stock immediately prior to such liquidation, dissolution, winding up or deemed liquidation. Should the Company’s legally available assets be insufficient to satisfy the Series A Stock liquidation preference, the funds were to be distributed with equal priority and pro rata among the holders of the Series A Stock in proportion to the preferential amount each holder was otherwise entitled to receive. After the payment to the holders of Series C Stock, Series B Stock and Series A Stock of the full preferential amounts, the entire remaining assets of the Company legally available for distribution were to be distributed with equal priority and pro rata among the holders of common stock in proportion to the number of shares of common stock held by them. Conversion — Each share of Series A Stock, Series B Stock and Series C Stock was convertible at the option of a holder at any time into a number of shares of the Company’s common stock at a conversion rate, which is the Series A Stock, Series B Stock and Series C Stock original issuance price, $1.9720, $10.2217 and $12.2661, respectively, divided by the Series A Stock, Series B Stock and Series C Stock conversion price in effect at the time of conversion. If, after the issuance date of the Series A Stock, Series B Stock and Series C Stock, the Company were to issue or sell, or was deemed to have sold, additional shares of common stock at a price lower than the original issuance price of the Series A Stock or Series B Stock or Series C Stock, except for certain exceptions, the conversion price of the Series A Stock and/or the Series B Stock and Series C Stock would be adjusted. The Series A Stock, Series B Stock and Series C Stock conversion prices were initially equal to the Series A Stock, Series B Stock and Series C Stock original issue prices, and were subject to recapitalization and other adjustments, as provided in the Company’s then-current certificate of incorporation. As of December 31, 2022, the conversion rates were one-for-one. Voting Rights — The holders of redeemable convertible preferred stock and the holders of common stock were to vote together and not as separate classes. Each holder of Series A Stock, Series B Stock and Series C Stock was entitled to the number of votes equal to the number of shares of common stock into which the shares of Series A Stock, Series B Stock and Series C Stock could be converted as of the record date. For as long shares of redeemable convertible preferred stock remained outstanding, Series A stockholders, Series B stockholders and Series C stockholders, voting as a separate class, were entitled to elect Series A, Series B and Series C members of the Board and had certain protective provisions, as defined in the then-current certificate of incorporation. The holders of redeemable convertible preferred stock and Class A Common Stock, voting together as a single class on an as-converted basis, were entitled to elect three mutual directors. Redemption — The redeemable convertible preferred stock was recorded in mezzanine equity because while it was not mandatorily redeemable, it would have become redeemable at the option of the preferred stockholders upon the occurrence of certain deemed liquidation events that are considered not solely within the Company’s control.

Derivative Tranche Liability

Derivative Tranche Liability	12 Months Ended
Derivative Tranche Liability	Dec. 31, 2023
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Tranche Liability	Derivative Tranche Liability In connection with the Series C First Tranche Closing, prior to the IPO closing, the Company had an obligation to sell, and investors of the Series C First Tranche Closing had an obligation to purchase, an additional 12,228,881 shares of Series C redeemable convertible preferred stock at $12.2661 per share on June 30, 2023. The obligation of each investor to purchase shares at the Series C Second Tranche Closing were subject to the fulfillment, on or before such closing, of certain conditions including not closing the Company’s first underwritten public offering of its Class A Common Stock under the Securities Act or the closing of a direct listing prior to June 30, 2023. The Series C Second Tranche Closing was terminated at the IPO closing, on May 9, 2023. Prior to May 9, 2023, the obligation to issue and purchase shares was concluded to be a forward contract derivative liability and was measured at fair value using a probability weighted model at the issuance date. The initial fair value of the forward contract was $10.8 million and was recorded as a derivative tranche liability. The Company used the following assumptions to estimate the liability as of the issuance date: probability of achieving milestone of 90%; expected term equals the contractual term from September 2022 until June 2023; Series C preferred stock fair value of $12.2661; and a discount rate of 25%. Following the termination of the Series C Second Tranche Closing at the closing of the IPO the Company recognized a gain on change in fair value of the derivative tranche liability in the amount of $10.3 million in the consolidated statements of operations and comprehensive loss for the year ended December 31, 2023.

Common Stock

Common Stock	12 Months Ended
Common Stock	Dec. 31, 2023
Equity [Abstract]
Common Stock	Common Stock On May 9, 2023, immediately prior to the IPO closing, each share of the Company’s Class A Common Stock then issued and outstanding was reclassified and became one share of the Company’s common stock. As of December 31, 2023 and 2022, there were no shares of Class B Common Stock outstanding. As of December 31, 2023 and 2022, the Company’s Common Stock reserved for future issuance was as follows: As of December 31, 2023 2022 Shares available for future grants under Equity Incentive Plan 3,526,392 1,570,353 Outstanding stock options 9,630,623 5,036,946 Performance-based restricted stock units 2,964,072 — Outstanding restricted stock units 2,166,016 1,107,213 Options assumed upon ValenzaBio acquisition 938,440 — ESPP Shares available for future grants 875,836 — Redeemable convertible preferred stock — 40,743,522 Total shares reserved for future issuance 20,101,379 48,458,034 Founders’ Common Stock On the IPO closing date, according to the terms of the restated certificate of incorporation, each share of the founders’ Class A Common Stock issued and outstanding was reclassified and became 1 share of the Company’s common stock; no vesting or other terms were modified. In July 2020, the Company issued 2,839,749 shares of its common stock to founders at a price of $0.00002 per share. The issuance price was the estimated fair value of the shares as the shares were issued at inception and no intellectual property was contributed by the founders. The founders have voting rights and rights to receive dividends regardless of the vesting of the shares. Issued shares vest monthly over 48 months, as founders continue providing services to the Company. The Company has the right to repurchase unvested shares at the price paid by the founders if services are terminated. Stock-based compensation expense was minimal for these shares. In December 2022, the Company repurchased 591,613 restricted common shares at the original purchase price that were unvested as of the date of repurchase in connection with one founder’s resignation. As of December 31, 2023 and 2022, 207,060 and 562,032 shares were unvested. During the years ended December 31, 2023 and 2022, 354,972 and 621,196 founders’ shares vested, respectively.

Equity Incentive Plan

Equity Incentive Plan	12 Months Ended
Equity Incentive Plan	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Equity Incentive Plan	Equity Incentive Plan In April 2023, the Company’s board of directors adopted, and stockholders approved, the 2023 Equity Incentive Plan (the “2023 Plan”) that became effective on May 4, 2023. The Company reserved, 12,000,000 new shares of common stock for issuance under the 2023 Plan. In addition, 6,920,846 shares issued and outstanding under the Company’s 2020 Equity Incentive Plan, as amended (the “2020 Plan”), have been added to the 2023 Plan as such shares become available from time to time if awards terminate, expire, or lapse for any reason without the delivery of shares, or are reacquired or withheld (or not issued) to satisfy a tax withholding obligation or the purchase or exercise price. The 2023 Plan also provides that the number of shares initially reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2024 and ending on January 1, 2033, by an amount equal to the lesser of (i) 5% of the shares of common stock outstanding on the last day of the immediately preceding fiscal year, and (ii) such smaller number of shares of stock as determined by the Company’s board of directors. No more than 56,762,538 shares of stock may be issued upon the exercise of incentive stock options under the 2023 Plan. The Company may grant incentive stock options, nonstatutory stock options (“NSOs”), restricted stock units (“RSUs”), restricted stock awards (“RSAs”), stock appreciation rights (“SARs”), performance awards and other awards to the Company’s officers, employees, directors and consultants. Options under the 2023 Plan may be granted for periods of up to 10 years at exercise prices no less than the fair market value of the common stock on the date of grant and usually vest over four years. The exercise price of an option granted to a 10% stockholder may not be less than 110% of the fair market value of the shares on the date of grant and such option may not be exercisable after the expiration of five years from the date of grant. The grant date fair market value of all awards made under our 2023 Plan and all cash compensation paid by us to any non-employee director for services as a director in any fiscal year may not exceed $750,000, increased to $1,000,000 in the fiscal year of their initial service as a non-employee director. The 2023 Plan is the successor to and continuation of the 2020 Plan and no additional awards may be granted under the 2020 Plan. All outstanding awards granted under the 2020 Plan will remain subject to the terms of the 2020 Plan. The 2020 Plan provided for the grant of incentive stock options, nonstatutory stock options, RSUs and RSAs to the Company’s officers, employees, directors and consultants. As of December 31, 2023, 3,526,392 shares of the Company’s common stock were reserved for issuance under the 2023 Plan. In April 2023, the Company’s board of directors and stockholders adopted the 2023 Employee Stock Purchase Plan (the “ESPP”), which became effective on May 4, 2023. The ESPP authorized issuance of up to 900,000 shares of common stock. The ESPP permits participants to purchase common stock through payroll deductions of up to 15% of their eligible compensation. Employees purchase shares of common stock at a price per share equal to 85% of the lower of the fair market value at the start or end of six-month purchase and offering consecutive periods. The aggregate number of shares reserved for sale under the 2023 ESPP will increase automatically on January 1 for a period of up to 10 calendar years, commencing on January 1, 2024, by the number of shares equal to the lesser of 1% of the Company's total outstanding shares of common stock on the immediately preceding December 31st, and 2,700,000 shares or a lesser number of shares as may be determined by the board of directors. There were 875,836 ESPP shares available for future grants as of December 31, 2023. Stock Options Stock options issued under the 2020 and 2023 Plan generally vest over a four A summary of option activity under the 2020 Plan and 2023 plan is as follows: Number of Weighted- Weighted- Aggregate Outstanding at December 31, 2022 5,036,946 $ 4.7872 9.5 $ 5,488 Options granted 6,196,917 $ 14.9001 Options exercised (330,506) $ 5.1507 Options expired (10,653) $ 18.0000 Options forfeited (1,262,081) $ 10.9333 Outstanding at December 31, 2023 9,630,623 $ 10.4619 9 $ 12,007 Exercisable at December 31, 2023 1,661,322 $ 4.4577 8.1 $ 5,226 Vested and expected to vest at December 31, 2023 9,630,623 $ 10.4619 9 $ 12,007 The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the estimated fair value of the Company’s common stock for those stock options that had exercise prices lower than the estimated fair value of the Company’s common stock at December 31, 2023 and 2022. Fair value of shares vested during the year ended December 31, 2023 was $10.6 million. The weighted-average grant date fair value of options granted in 2023 was $8.8732. ValenzaBio 2020 Stock Option Plan On January 4, 2023, in connection with the Acquisition, the Company assumed the ValenzaBio 2020 Stock Option Plan and options to issue 1,249,811 shares of the Company’s Class A Common Stock to ValenzaBio option holders, who entered into consulting agreements with the Company. The weighted-average exercise price of assumed options was $3.6736 per share. Under the terms of the Merger Agreement, the assumed options vested in full on March 31, 2023. A total of 311,371 options assumed under the ValenzaBio 2020 Stock Option Plan having the weighted-average exercise price of $2.4921 were exercised for the year ended December 31, 2023. The Company recognized the full amount of stock-based compensation expense of $4.9 million, including $3.1 million as research and development expenses and $1.8 million as general administrative expenses, related to assumed options in the consolidated statement of operations for the year ended December 31, 2023. Restricted Stock Units In 2022, the Company granted RSU awards for 1,107,213 shares vesting based on satisfaction of certain service and liquidity conditions. On March 23, 2023, the Board approved the acceleration of vesting of 138,401 RSUs. The Company accounted for the changes in vesting terms as a modification and re-measured modified awards at fair value on the modification date. The estimated fair value of RSUs granted was $8.0 million after modification. On May 9, 2023, the IPO closing date, 640,416 RSUs vested and the Company recognized $5.5 million stock-based compensation expense. The Company issued 303,237 shares and withheld 337,179 shares to satisfy tax withholding obligations of $8.3 million paid upon the RSU settlement. On August 16, 2023, the company granted 1,725,168 RSUs shares to certain employees of the Company, which shall vest in four Remaining unvested RSUs were 2,166,016 as of December 31, 2023. A summary of unvested RSU activity is presented in the following table: Number of RSUs Weighted-Average Grant Date Fair Value Unvested at December 31, 2022 1,107,213 $ 5.42 Granted 1,725,168 28.15 Vested (640,416) 6.65 Forfeited (25,949) 26.97 Unvested at December 31, 2023 2,166,016 $ 22.90 Performance-Based Restricted Stock Units In August 2023, the Company granted PSUs to certain employees and officers of the Company. The PSUs may vest over several years subject to the achievement of (i) certain clinical development milestones over a performance period from the grant date to May 2027 (the “Performance Period”) or (ii) market conditions (i.e., stock price hurdle) based on pre-specified volume-weighted average stock price measurements as of each vesting performance measurement date, and continued employment with the Company through the applicable vesting date(s). The target number of shares under the PSUs is 3,135,104. The ultimate number of PSU shares that may vest, in the aggregate over the Performance Period, could in certain cases be up to 150% of the target number of shares upon the achievement of certain market or performance conditions. A summary of PSU activity based on the target number of shares is presented in the following table: Number of PSUs Weighted-Average Grant Date Fair Value* Outstanding at December 31, 2022 — $ — Granted 3,135,104 27.43 Vested — — Forfeited (171,032) 27.43 Outstanding at December 31, 2023 2,964,072 $ 27.43 *The grant date fair value is based only on the PSUs with market conditions and does not factor in any performance conditions. As the PSUs granted in 2023 are subject to a market condition, the grant date fair value for such PSUs was based on a Monte Carlo simulation model. The Company estimated the fair value of PSUs based on the grant date price of its common stock of $26.97 and the following assumptions: expected volatility of 87.71%, risk-free-rate of 4.47%, and zero expected dividend yield. In 2023, the Company granted PSUs to employees with a weighted-average grant date fair value of $27.43. The unvested awards will expire if it is determined that the vesting conditions have not been met during the applicable three-year performance period. 2023 Employee Stock Purchase Plan The first purchase period commenced on June 15, 2023 and ended on December 14, 2023. The Company recorded less than $0.1 million in accrued liabilities as of December 31, 2023. During the year ended December 31, 2023, the Company's employees purchased a total of 24,164 shares under the 2023 ESPP at a total purchase price of $0.1 million. Stock-Based Compensation Expense The Black-Scholes option pricing model used to estimate fair value of stock-based awards requires the use of the following assumptions: • Fair value of common stock. Prior to the Company's IPO, the fair market value of the Company’s common stock is determined by the Board with assistance from management and external valuation experts. The approach to estimating the fair market value of common stock is consistent with the methods outlined in the American Institute of Certified Public Accountants’ Accounting and Valuation Guide, Valuation of Privately-Held Company Equity Securities Issued as Compensation ( the “Practice Aid”). For valuations performed prior to December 31, 2021 , the Company utilized an Option Pricing Method (“OPM”) based analysis, primarily the OPM backsolve methodology, to determine the estimated fair value of the common stock. Within the OPM framework, the backsolve method for inferring the total equity value implied by a recent financing transaction involves the construction of an allocation model that takes into account the Company’s capital structure and the rights, preferences and privileges of each class of stock, then assumes reasonable inputs for the other OPM variables (expected time to liquidity, volatility, and risk-free rate). The total equity value is then iterated in the model until the model output value for the equity class sold in a recent financing round equals the price paid in that round. The OPM is generally utilized when specific future liquidity events are difficult to forecast (i.e., the enterprise has many choices and options available), and the enterprise’s value depends on how well it follows an uncharted path through the various possible opportunities and challenges. In determining the estimated fair value of the common stock, the Board also considered the fact that the stockholders could not freely trade the common stock in the public markets. Accordingly, the Company applied discounts to reflect the lack of marketability of its common stock based on the weighted-average expected time to liquidity. The estimated fair value of the common stock at each grant date reflected a non-marketability discount partially based on the anticipated likelihood and timing of a future liquidity event. For valuations performed after December 31, 2021 in accordance with the Practice Aid the Company utilized the hybrid method for determining the fair value of our Class A Common Stock based on the Company’s stage of development and other relevant factors. The hybrid method is a probability-weighted expected return method (PWERM), where the equity value in one or more scenarios is calculated using an OPM. The PWERM is a scenario-based methodology that estimates the fair value of Class A Common Stock based upon an analysis of future values for the company, assuming various outcomes. The Class A Common Stock value is based on the probability-weighted present value of expected future investment returns considering each of the possible outcomes available as well as the rights of each class of stock. The future value of the Class A Common Stock under each outcome is discounted back to the valuation date at an appropriate risk-adjusted discount rate and probability weighted to arrive at an indication of value for the Class A Common Stock. A discount for lack of marketability of the Class A Common Stock was then applied to arrive at an indication of value for the Class A Common Stock. The Company also considered the amount of time between the independent third-party valuation dates and the grant date of an award. The Company interpolated the common stock fair value between the two valuation dates, if there were any significant internal or external events occurred during this period. The incremental stock-based compensation expense recorded as a result of the retrospective review was insignificant. Following the Company's IPO, the fair market value of the Company's common stock is based on its closing price on Nasdaq as reported on the date of the stock option grant. • Expected term. The expected term represents the period that the stock-based awards are expected to be outstanding. The expected term for the Company’s stock options was calculated based on the weighted-average vesting term of the awards and the contract period, or simplified method. • Expected volatility. The expected volatility is estimated based on the average historical volatilities of common stock of comparable publicly traded entities over a period equal to the expected term of the stock option grants as the Company does not have sufficient trading history for its publicly traded common stock. The comparable companies were chosen based on their size, stage of their life cycle or area of specialty. The Company will continue to apply this process until enough historical information regarding the volatility of its stock price becomes available. • Risk-free interest rate. The risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the expected term of the awards. • Expected dividend yield. The Company has never paid dividends on the common stock and has no plans to pay dividends on the common stock. Therefore, the Company used an expected dividend yield of zero. The Company used the following assumptions to estimate fair value of each option at the grant date for the years ended December 31, 2023, 2022 and 2021: Year Ended December 31, 2023 2022 2021 Expected volatility 85.17% - 94.74% 96.33% - 102.81% 99.97% - 100.78% Expected dividend yield 0 % 0 % 0 % Expected term (in years) 5.77 - 6.08 years 5.88 - 6.08 years 5.93 - 6.06 years Risk-free interest rate 3.30% - 4.80% 1.69% - 3.96% 0.87% - 0.97% The following table presents the classification of stock-based compensation expense related to awards granted to employees and non-employees (in thousands): Year Ended December 31, 2023 2022 2021 Research and development expenses $ 12,652 $ 1,373 $ 214 General and administrative expenses 34,666 2,679 19 Total stock-based compensation expense $ 47,318 $ 4,052 $ 233 The stock-based compensation expense relates to the following equity-based awards: Year Ended December 31, 2023 2022 2021 Restricted stock units $ 11,726 $ — $ — Performance-based restricted stock units 12,109 — — Stock options 23,281 2,035 233 ESPP 202 — — Restricted stock awards — 2,017 — Total stock-based compensation expense $ 47,318 $ 4,052 $ 233

Related Party Transactions

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions During the years ended December 31, 2023, and 2021 the Company did not enter into transactions with related parties outside of the ordinary course of the business. During the year ended December 31, 2022, the Company paid $10,000 to one of the stockholders as a reimbursement of Series B Stock issuance costs.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	12 Months Ended
Net Loss Per Share Attributable to Common Stockholders	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common Stockholders The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2023 2022 2021 Numerator: Net loss $ (381,641) $ (64,772) $ (41,839) Denominator: Weighted average common shares outstanding 70,647,093 3,271,978 2,843,305 Less: Weighted-average common shares subject to repurchase (397,513) (1,714,444) (2,155,907) Weighted-average common shares outstanding, basic and diluted 70,249,580 1,557,534 687,398 Net loss per share attributable to common stockholders, basic and diluted $ (5.43) $ (41.59) $ (60.87) The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive: As of December 31, 2023 2022 2021 Outstanding options to purchase common stock 9,630,623 5,036,946 481,994 Unvested RSUs outstanding 2,166,016 1,107,213 — Outstanding options to purchase common stock assumed upon the ValenzaBio acquisition 938,440 — — Common stock subject to repurchase 207,060 562,032 1,774,841 ESPP 87,356 — — Redeemable convertible preferred stock — 40,743,522 16,285,718 Total 13,029,495 47,449,713 18,542,553 The table above does not include contingently issuable PSUs with market or performance vesting conditions, given as of December 31, 2023, the performance conditions were not deemed probable to be achieved (see Note 12).

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes No provision for income taxes was recorded for the year ended December 31, 2023, 2022 and 2021, as the Company operated with taxable losses. The Company has incurred net operating losses only in the United States since its inception. A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate was as follows: Year Ended December 31, 2023 2022 2021 Income tax computed at federal statutory rate 21.00 % 21.00 % 21 % State taxes 0.07 0.71 0.26 Other permanent differences (1.03) (0.43) (0.11) Research credits 1.12 1.40 0.19 Change in valuation allowance (14.38) (22.68) (21.34) IPR&D (6.78 %) — % — % Effective income tax rate — % — % — % Significant components of the deferred tax assets and liabilities were as follows (in thousands): Year Ended December 31, 2023 2022 Deferred Tax Assets: Net operating loss carry forwards $ 19,640 $ 6,203 Capitalized R&E expenditures 52,911 10,814 Intangibles 14,439 4,785 Research credits 6,898 1,259 Lease liability 298 — Other 4,782 676 Total deferred tax assets 98,968 23,737 Less: Valuation allowance (98,716) (23,737) Net deferred tax assets $ 252 $ — Right-of-use asset (ROU) $ (252) $ — Net deferred tax liability $ (252) $ — Total net deferred tax assets $ — $ — Beginning January 1, 2022, the Tax Cuts and Jobs Act, or the Tax Act, eliminated the option to deduct research and development expenditures in the current year and requires taxpayers to capitalize such expenses pursuant to Internal Revenue Code Section 174. The capitalized expenses are amortized over a 5-year period for domestic expenses and a 15-year period for foreign expenses. A valuation allowance is required to be established when it is more likely than not that all or a portion of a deferred tax asset will not be realized. Realization of deferred tax assets is dependent upon future earnings, the timing and amount of which are uncertain. The Company believes that, based on a number of factors such as the history of operating losses, it is more likely than not that the deferred tax assets will not be fully realized, such that a full valuation allowance has been recorded. The balance of the valuation allowance was less than $0.1 million beginning January 1, 2021. The valuation allowance increased by $75.0 million, $14.7 million, and $8.9 million, for the years ended December 31, 2023 and 2022 and 2021, respectively, primarily due to changes in capitalized R&D expenditures, net operating loss carry forwards, research and development credits, and capitalization of certain intangibles. The following table sets forth the Company’s federal and state net operating loss carryforwards and tax credits as of December 31, 2023 (dollars in thousands): Amount Begin to Expire Net operating losses, Federal $ 92,703 Do not expire Net operating losses, State $ 6,820 2041 Tax credits, Federal $ 8,320 2041 Tax credits, California $ 1,110 Do not expire Federal and state laws impose substantial restrictions on the utilization of net operating loss and tax credit carryforwards in the event of an ownership change for tax purposes, as defined in Section 382 of the Internal Revenue Code. As a result of such ownership changes, the annual limitation may result in the expiration of net operating losses and credits before utilization. The Company has experienced ownership changes in the past and in the current year. We completed a Section 382 analysis through December 31, 2023, and concluded that although an ownership change had occurred, the Company's net operating losses and credits were substantially free of limitations as of December 31, 2023. Uncertain Tax Positions A reconciliation of the beginning and ending balances of the unrecognized tax benefits during the year ended December 31, 2023, 2022 and 2021 are as follows (in thousands) Year Ended December 31, 2023 2022 2021 Beginning balance $ 516 $ 48 $ — Increase in tax positions in the current period 1,600 468 48 Additions for tax positions of prior years 233 — — Ending balance $ 2,348 $ 516 $ 48 The entire amount of the unrecognized tax benefits would not impact the Company’s effective tax rate if recognized. The Company has elected to include interest and penalties as a component of tax expense. The Company determined that no accrual for interest and penalties related to unrecognized tax benefits was required as of December 31, 2023, 2022 and 2021. The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease during the next 12 months. The Company is subject to examination by the U.S. federal and state tax authorities from inception to December 31, 2023. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service and state tax authorities to the extent utilized in a future period.

Subsequent Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events In November 2023, we disclosed a vendor programming error caused a dose-sequencing error in the 160 mg every other week and 80mg every four weeks dosing arms of our Phase 2b/3 trial in Psoriatic Arthritis. In connection with this error, on March 10, 2024, we entered into arrangements with certain vendors that enabled a multi-party solution where we have received in the first quarter of 2024, a payment of $30.0 million and a $5 million service credit.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and include operations of the Company and its wholly owned subsidiary, WH 2 LLC (the legal successor of ValenzaBio). These subsidiaries were formed in contemplation of the Acquisition and did not have any operations and any balances from inception to December 31, 2023.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of expenses during the reporting period. On an ongoing basis, the Company evaluates estimates and assumptions, including but not limited to those related to the fair value of its derivative tranche liability, the fair value of its common stock, stock-based compensation expense, accruals for research and development expenses, fair value of in-process research and development assets acquired, valuation of deferred tax assets, and uncertain income tax positions. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates or assumptions.
Segment Information	Segment Information The Company has one operating segment. The Company’s focus is the research, development and commercialization of product candidates. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for allocating and evaluating financial performance. All long-lived assets are maintained in the United States of America.
Cash and Cash Equivalents	Cash and Cash Equivalents
Short-Term Marketable Securities	Short-Term Marketable Securities Investments with original maturities of greater than 90 days are classified as available-for-sale marketable securities and consist primarily of U.S. Treasury obligations, corporate debt obligations and federal agency obligations. As the Company’s entire investment portfolio is considered available for use in current operations, the Company classifies all investments as available-for-sale and as current assets, even though the stated maturity may be more than one year from the current balance sheet date. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive loss, which is a separate component of stockholders’ equity (deficit) in the consolidated balance sheet. Interest income includes interest, amortization of purchase premiums and discounts, realized gains and losses on sales of securities and other-than-temporary declines in the fair value of investments, if any. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity, which are both recorded to interest income in the Company’s consolidated statement of operations and comprehensive loss. Changes in the fair value of available-for-sale securities impact the consolidated statement of operations and comprehensive loss only when such securities are sold if an allowance for credit losses is recognized or if an impairment is recognized. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. The Company regularly reviews its investment portfolio to determine if any security is impaired, which would require the Company to record an allowance for credit losses or impairment charge in the period any such determination is made. In making this judgment, the Company evaluates, among other things, the duration and extent to which the fair value of a security is less than its cost, its intent to sell or whether it is more likely than not that the Company will be required to sell the security before recovery of its amortized cost basis, the financial condition of the issuer and any changes thereto, and, as necessary, the portion of a decline in fair value that is credit-related. This assessment could change in the future due to new developments or changes in assumptions related to any particular security. Realized gains and losses, allowances for credit losses and impairments on available-for-sale securities, if any, are recorded to interest expense, net in the consolidated statement of operations and comprehensive loss.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The carrying amounts of cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other liabilities, approximate fair value due to their short-term maturities. Financial instruments, such as money market funds, short-term marketable securities and derivative tranche liability are measured at fair value at each reporting date (see Note 4). The Company discloses and recognizes the fair value of its assets and liabilities using a hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to valuations based upon unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to valuations based upon unobservable inputs that are significant to the valuation (Level 3 measurements). The guidance establishes three levels of the fair value hierarchy as follows: Level 1 —Observable inputs, such as quoted prices in active markets for identical assets or liabilities. Level 2 —Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and considers factors specific to the asset or liability. The Company recognizes transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs. The Company’s financial instruments measured at fair value on a recurring basis consist of Level 1, Level 2, and Level 3 financial instruments. Usually, short-term marketable securities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. Corporate debt obligations, commercial paper, government agency obligations and asset-backed securities are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. Financial assets and liabilities are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies, or similar techniques, and at least one significant model assumption or input is unobservable.
Concentration of Credit Risk	Concentration of Credit Risk Cash and cash equivalents, and short-term marketable securities are financial instruments that potentially subject the Company to concentrations of credit risk. As of December 31, 2023 and 2022, cash consists of cash deposited with one financial institution and account balances exceed federally insured limits. Management believes that the Company is not exposed to significant credit risk due to the financial strength of this institution. The Company also has investments in money market funds, U.S. Treasury obligations, corporate debt obligations, and federal agency obligations, which can be subject to certain credit risks. The Company mitigates the risks by investing in high-grade instruments, limiting its exposure to any one issuer and monitoring the ongoing creditworthiness of the financial institutions and issuers. The Company has not experienced any losses on its financial instruments.
Risks and Uncertainties	Risks and Uncertainties The Company is subject to certain risks and uncertainties, including, but not limited to, changes in any of the following areas that the Company believes could have a material adverse effect on the future financial position or results of operations: the timing of, and the Company’s ability to advance its current and future product candidates into and through clinical development; costs and timelines associated with the manufacturing of clinical supplies for the Company’s product candidates; regulatory approval and market acceptance of, and reimbursement for its product candidates; performance of third-party vendors; competition from companies with greater financial resources or expertise; protection of the intellectual property; litigation or claims made by or against the Company based on intellectual property or other factors; compliance with government regulations; and its ability to attract and retain employees necessary to support its growth. The Company has expended and will continue to expend substantial funds to complete the research, development and clinical testing of its product candidates. The Company also will be required to expend additional funds to establish commercial-scale manufacturing arrangements and to provide for the marketing and distribution of products that receive regulatory approval. If any of its product candidates are approved, the Company will require additional funds to commercialize its products. The Company is unable to entirely fund these efforts with its current financial resources. If adequate funds are unavailable on a timely basis from additional sources of financing, the Company may have to delay, reduce the scope of or eliminate one or more of its research or development programs, which would materially and adversely affect its business, financial condition and operations.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty of the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses in the consolidated statements of operations and comprehensive loss.
Asset Acquisitions and Acquired In-Process Research and Development Expenses	Asset Acquisitions and Acquired In-Process Research and Development Expenses The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the asset or group of assets, which includes transaction costs. The Company determined that ValenzaBio acquisition should be accounted for as an asset acquisition after considering whether substantially all of the fair value of the gross assets acquired was concentrated in a single asset or group of assets and whether the Company acquired a substantive process capable of significantly contributing to the Company’s ability to create outputs. The fair value of in-process research and development assets is determined based on the present value of future discounted cash flows. Contingent consideration in asset acquisitions payable in the form of cash is recognized in the period the triggering event is determined to be probable of occurrence and the related amount is reasonably estimable. Such amounts are expensed or capitalized based on the nature of the associated asset at the date the related contingency is resolved.
Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock The Company records shares of redeemable convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The redeemable convertible preferred stock is recorded outside of permanent equity because while it is not mandatory, redemption is contingent upon the occurrence of certain events considered not solely within the Company’s control. The Company has not adjusted the carrying values of the redeemable convertible preferred stock to the liquidation preferences of such shares because a deemed liquidation event obligating the Company to pay the liquidation
Derivative Tranche Liability	Derivative Tranche Liability In connection with the initial closing of the Series C preferred stock financing in September 2022, the Company had a commitment and Series C investors had an obligation to purchase the Series C Second Tranche at a fixed price, if specified conditions were met on June 30, 2023. The obligation to issue additional shares of Series C redeemable convertible preferred stock at a future date was determined to be a freestanding derivative instrument and was accounted for as a liability. The derivative tranche liability was accounted for at fair value at the issuance date and remeasured at the end of each reporting period until the shares are issued or the obligation expires. Changes in the fair value of the derivative tranche liability are recognized in the consolidated statement of operations and comprehensive loss.
Research and Development Expense and Accrued Liabilities	Research and Development Expenses and Accrued Liabilities Research and development costs are expensed as incurred. Research and development costs include salaries, stock-based compensation, and benefits for employees performing research and development activities, expenses incurred under agreements with consultants, third parties’ organizations and vendors that conduct clinical studies, other supplies and costs associated with product development efforts, preclinical activities, and regulatory operations. Payments associated with licensing agreements to acquire exclusive licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternate future use are also expensed as incurred. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are capitalized and recorded in prepaid expenses and other current assets, and then expensed as the related goods are delivered or the services are performed. The Company records accrued liabilities for estimated costs of its research and development activities conducted by third-party service providers. The Company accrues these costs based on factors such as estimates of the work completed and in accordance with the third-party service agreements. If the Company does not identify costs that have begun to be incurred or if the Company underestimates or overestimates the level of services performed or the costs of these services, actual expenses could differ from the estimates. To date, the Company has not experienced any material differences between accrued costs and actual costs incurred. The Company makes payments in connection with clinical trials to contract manufacturing organizations (“CMOs”) that manufacture the material for its product candidates and to clinical research organizations (“CROs”) and clinical trial sites that conduct and manage the Company’s clinical trials. The financial terms of these contracts are subject to negotiation, which vary by contract and may result in payments that do not match the periods over which materials or services are provided. Generally, these agreements set forth the scope of work to be performed at a fixed fee, unit price or on a time and materials basis. In the event the Company makes advance payments for goods or services that will be used or rendered for future research and development activities, the payments are deferred and capitalized as a prepaid expense and recognized as expense as the goods are received or the related services are rendered. These payments are evaluated for current or long-term classification based on when they are expected to be realized.
Stock-Based Compensation Expense	Stock-Based Compensation Expense The Company grants stock-based equity awards including restricted stock awards, restricted stock units, performance-based restricted stock units, and stock options to employees and members of its board of directors (the “Board”). These awards are accounted at fair value on the award grant date. Stock-based compensation expense is recognized over the awards’ vesting period on a straight-line basis and recorded as either research and development or general and administrative expenses in the statements of operations and comprehensive loss based on the function to which the related services are provided. Forfeitures are accounted for as they occur. Performance-based restricted stock units (“PSUs”), awarded to employees vest upon the achievement of certain performance milestones and market conditions (i.e., specified average stock price hurdle) at the end of specified performance periods, subject to continuous service through each respective vest date. The amount of expense recognized is based on the grant date fair value of the PSU tranche corresponding to the performance condition of the tranche which is considered probable. The estimated grant date fair value of the market portion of the PSUs is based on a Monte Carlo simulation under each performance condition outcome. The Monte Carlo valuation model simulates the probabilities of stock price achievement, which requires management to make a number of assumptions including a 20-trading day volume-weighted average stock price, volatility of our peers, and the risk-free interest rate. Compensation expense for each tranche of a PSU award is recognized straight-line over the period commencing on the grant date of the award and ending on the vesting date of the tranche under the PSU award. Cumulative adjustments are recorded at each reporting date to reflect subsequent changes to the estimated outcome of the performance condition until the end of the respective performance period. The Company uses the Black-Scholes option pricing model to determine the fair value of stock options and restricted stock awards if these are similar to early exercised options. The use of the Black-Scholes option pricing model requires the Company to make assumptions with respect to the fair value of the Company’s common stock at grant date, expected term of the option, the expected volatility of the common stock consistent with the expected life of the option, risk-free interest rates and expected dividend yields of the common stock. The Company estimates the fair value of restricted stock units based on the fair value of the Company’s common stock at a grant date. Stock-based compensation expense related to stock options granted to non-employees is recognized based on the fair value of the stock options, determined using the Black-Scholes option pricing model. The awards generally vest over the time period the Company expects to receive service from the non-employee.
Foreign Currency Transactions	Foreign Currency Transactions Transactions denominated in foreign currencies are initially measured in U.S. dollars using the exchange rate on the date of the transaction. Foreign currency denominated monetary assets and liabilities are subsequently remeasured at the end of each reporting period using the exchange rate at that date, with the corresponding foreign currency transaction gain or loss recorded in the statements of operations and comprehensive loss.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. In evaluating the ability to recover deferred income tax assets, the Company considers all available positive and negative evidence, including operating results, ongoing tax planning and forecasts of future taxable income on a jurisdiction-by-jurisdiction basis. In the event the Company determines that it would be able to realize deferred income tax assets in the future in excess of their net recorded amount, the Company would make an adjustment to the valuation allowance that would reduce the provision for income taxes. Conversely, in the event that all or part of the net deferred tax assets are determined not to be realizable in the future, an adjustment to the valuation allowance would be charged to earnings in the period when such determination is made. As of December 31, 2023 and 2022, the Company had recorded a full valuation allowance on deferred tax assets. Tax benefits related to uncertain tax positions are recognized when it is more likely than not that a tax position will be sustained during an audit. The tax benefit recognized is measured as the largest amount of benefit which is more likely than not to be realized upon settlement with the taxing authority. Changes in recognition or measurement are reflected in the period in which the change in judgement occurs. Interest and penalties related to unrecognized tax benefits are included within the provision for income tax.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common Stockholders Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period, without consideration of potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock and potentially dilutive securities outstanding for the period.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. The Company’s other comprehensive income (loss) is comprised solely of unrealized gains (losses) on available-for-sale marketable securities. The Company has not recorded any reclassifications from other comprehensive income (loss) to net loss during the period presented.
Leases	Leases The Company adopted ASU 2016-02, “Leases (Topic 842)” accounting standard as of January 1, 2022. The contractual arrangements that meet the definition of a lease are classified as operating or finance leases and are recorded on the balance sheets as both a right-of-use asset (“ROU asset”) and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company’s incremental borrowing rate (“IBR”). Lease ROU assets and lease obligations are recognized based on the present value of the future minimum lease payments over the lease term at the lease commencement date. The Company currently does not have any finance leases. Operating lease ROU assets are adjusted for (i) payments made at or before the commencement date, (ii) initial direct costs incurred, and (iii) tenant incentives under the lease. As the implicit rate for the operating leases are not determinable, the Company determines its IBR based on the information available at the applicable lease commencement date. The IBR is determined by using the rate of interest that the Company would pay to borrow on a collateralized basis an amount equal to the lease payments for a similar term and in a similar economic environment where the asset is located. The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably certain the Company will exercise any option to extend the contract. Lease costs for minimum lease payments for operating leases are recognized on a straight-line basis over the lease term. Lease liabilities are increased by interest and reduced by payments each period, and the ROU asset is amortized over the lease term. Variable lease costs are recorded when incurred. In measuring the ROU assets and lease liabilities, the Company has elected to combine lease and non-lease components. The Company excludes short-term leases, if any, having initial terms of 12 months or less at lease commencement as an accounting policy election, and recognizes rent expense on a straight-line basis over the lease term for these types of leases.
Recent Accounting Pronouncements and Recently Adopted Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (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, as amended (the “JOBS Act”), 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. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted for nonpublic companies. In November 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which requires all public entities, including public entities with a single reportable segment, to provide in interim and annual periods one or more measures of segment profit or loss used by the chief operating decision maker to allocate resources and assess performance. In addition, this guidance requires disclosures of significant segment expenses and other segment items as well as incremental qualitative disclosures. This guidance is effective for fiscal years beginning after December 15, 2023, and interim periods after December 15, 2024, with retrospective application required, and early adoption permitted. The Company is currently in the process of evaluating the effects of this guidance on its related disclosures. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which requires enhanced income tax disclosures, including specific categories and disaggregation of information in the effective tax rate reconciliation, disaggregated information related to income taxes paid, income or loss from continuing operations before income tax expense or benefit, and income tax expense or benefit from continuing operations. This guidance is effective for annual periods beginning after December 15, 2024, with early adoption permitted. The Company is currently in the process of evaluating the impact of this pronouncement on its related disclosures.

ValenzaBio Acquisition (Tables)

ValenzaBio Acquisition (Tables)	12 Months Ended
ValenzaBio Acquisition (Tables)	Dec. 31, 2023
Business Combination and Asset Acquisition [Abstract]
Asset Acquisition	The following table represents the total purchase consideration (in thousands): Issued Class A Common Stock (1) $ 128,735 Transaction costs (2) 1,271 Cash (3) 8 Total $ 130,014 (1) Shares were issued for consideration at $6.86 per share, including 2,013,673 shares that were being held by Seller LLC until the Holdback Release Date. The Company used a third party valuation specialist to assist management in determining the fair value of the shares of Class A Common Stock at the Closing Date. (2) Legal and advisory transaction costs of $1.3 million incurred by the Company in connection with the Acquisition, including $0.1 million payable in cash to Seller LLC for the expense fund. (3) Cash payment of $7,663 to one non-accredited investor for settlement of vested ValenzaBio options. The following is the allocation of the purchase consideration to the acquired assets and liabilities (in thousands): Cash $ 11,369 Prepaid expenses and other current assets 2,074 In-process research and development assets 123,057 Accounts payable (1,628) Accrued research and development expenses (4,805) Accrued compensation and other current liabilities (53) Total net asset acquired $ 130,014

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
Fair Value Measurements (Tables)	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Schedule of Financial Instruments Measured on Recurring Basis	The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): Fair Value Measurements as of December 31, 2023 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash and cash equivalents) $ 23,205 $ 23,205 $ — $ — U.S. Treasury obligations ($146,497 included in cash and cash equivalents) 525,353 — 525,353 — Corporate debt obligations ($23,313 included in cash and cash equivalents) 135,284 — 135,284 — Federal agency obligations ($15,344 included in cash and cash equivalents) 27,746 — 27,746 — Total fair value of assets $ 711,588 $ 23,205 $ 688,383 $ — Fair Value Measurements as of December 31, 2022 Total Level 1 Level 2 Level 3 Assets: Money market funds (included in cash and cash equivalents) $ 238,223 $ 238,223 $ — $ — U.S. Government bonds 25,459 — 25,459 — U.S. Treasury bills 11,404 11,404 — — Corporate debt obligations 2,141 — 2,141 — Federal agency obligations 8,506 — 8,506 — Total fair value of assets $ 285,733 $ 249,627 $ 36,106 $ — Liabilities: Derivative tranche liability $ 10,291 $ — $ — $ 10,291 Total fair value of liabilities $ 10,291 $ — $ — $ 10,291 Classified as: December 31, 2023 December 31, 2022 Cash and cash equivalents $ 208,359 $ 238,223 Short-term marketable securities 503,229 47,510 Total cash equivalents and marketable securities $ 711,588 $ 285,733
Summary of Changes in Level 3 Liabilities	The following table sets forth the changes in the fair value of Level 3 liabilities (in thousands): Derivative Tranche Liability 2023 2022 Balance as of January 1st $ 10,291 $ — Fair value of derivative tranche liability upon issuance — 10,778 Change in fair value (10,291) (487) Balance as of December 31st $ — $ 10,291
Summary of Significant Assumptions Used to Estimate Fair Value	The following significant assumptions were used to estimate fair value of the derivative tranche liability as of December 31, 2022: Probability of achieving specified conditions 80 % Fair value of Series C preferred stock share $ 12.2661 Discount rate 25 %

Available-For-Sale Marketable_2

Available-For-Sale Marketable Securities (Tables)	12 Months Ended
Available-For-Sale Marketable Securities (Tables)	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Schedule of Available-for-Sale Marketable Securities	The following tables summarize the estimated fair value of the Company’s available-for-sale marketable securities as of December 31, 2023 and 2022 (in thousands): As of December 31, 2023 Total Total Unrealized Gain Total Total Money market funds (included in cash and cash equivalents) $ 23,205 $ — $ — $ 23,205 U.S. Treasury obligations ($146,497 included in cash and cash equivalents) 525,198 156 (1) 525,353 Corporate debt obligations ($23,313 included in cash and cash equivalents) 135,288 36 (40) 135,284 Federal agency obligations ($15,344 included in cash and cash equivalents) 27,735 12 (1) 27,746 Total available for sale marketable securities $ 711,426 $ 204 $ (42) $ 711,588 As of December 31, 2022 Total Total Unrealized Loss (1) Total Money market funds (included in cash and cash equivalents) $ 238,223 $ — $ 238,223 U.S. Government bonds 25,506 (47) 25,459 U.S. Treasury obligations 11,430 (26) 11,404 Corporate debt obligations 2,145 (4) 2,141 Federal agency obligations 8,515 (9) 8,506 Total available for sale marketable securities $ 285,819 $ (86) $ 285,733 ______________ (1) The Company did not have any gross unrealized gains as of December 31, 2022.

Consolidated Balance Sheet Co_2

Consolidated Balance Sheet Components (Tables)	12 Months Ended
Consolidated Balance Sheet Components (Tables)	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure	Prepaid expenses and other current assets consist of the following (in thousands): As of December 31, 2023 2022 Prepaid research and development expenses $ 8,184 $ 682 Value-Added Tax (VAT) receivable 3,985 — Prepaid insurance and other current assets 1,712 86 Interest receivable 764 138 Prepaid other services 667 288 Research and development credit receivable — 250 $ 15,312 $ 1,444 Other non-current assets consist of the following (in thousands): As of December 31, 2023 2022 Prepaid research and development expenses, non-current $ 2,644 $ 1,964 Security deposits 34 — Acquisition transaction costs — 1,121 Deferred IPO offering costs — 774 $ 2,678 $ 3,859
Property, Plant and Equipment	Property, plant and equipment consisted of the following as of December 31, 2023 (in thousands) : December 31, 2023 Construction in progress $ 1,460 Computer and other equipment 407 Furniture and fixtures 306 Leasehold improvements 121 Total property, plant and equipment, gross 2,294 Less: accumulated depreciation and amortization (115) Property, plant and equipment, net $ 2,179
Accrued Research and Development Expense	Accrued research and development expenses are comprised of the following (in thousands): As of December 31, 2023 2022 Accrued clinical manufacturing expenses $ 22,232 $ 1,292 Accrued clinical expenses 13,204 4,425 $ 35,436 $ 5,717
Other Current Liabilities	Accrued compensation and other current liabilities are comprised of the following (in thousands): As of December 31, 2023 2022 Accrued compensation $ 5,417 $ 3,068 Accrued professional services fees (1) 1,099 808 Other accrued expenses and current liabilities 317 361 $ 6,833 $ 4,237 (1) IPO offering costs included in accrued liabilities were zero and $0.2 million as of December 31, 2023 and December 31, 2022, respectively.

Commitments and Contingent Li_2

Commitments and Contingent Liabilities (Tables)	12 Months Ended
Commitments and Contingent Liabilities (Tables)	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Schedule of Non-cancellable Purchase Obligations	Non-cancelable purchase obligations for services to be performed or product to be manufactured, as of December 31, 2023 amount to: 2024 67,567 2025 53,686 2026 20,985 2027 and thereafter 106 Total $ 142,344
Summary of Operating Lease Liabilities	The following table summarizes a maturity analysis of the Company’s operating lease liabilities showing the aggregate lease payments as of December 31, 2023 (in thousands): 2024 375 2025 386 2026 398 2027 409 2028 280 Total future lease payments 1,848 Less imputed interest (434) Total operating lease liability balance 1,414 Less current portion of lease liability (included in accrued compensation and other current liabilities) (220) Operating lease liability, non-current $ 1,194

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
Redeemable Convertible Preferred Stock (Tables)	Dec. 31, 2023
Temporary Equity [Abstract]
Schedule of Convertible Preferred Stock	The authorized, issued, and outstanding shares of the Company’s convertible preferred stock and liquidation preferences as of December 31, 2022 were as follows (in thousands, except for share amounts): December 31, 2022 Shares Shares Issued Aggregate Net Series A redeemable convertible preferred stock 8,000,000 4,056,795 $ 8,000 $ 7,916 Series B redeemable convertible preferred stock 48,230,900 24,457,846 250,000 249,678 Series C redeemable convertible preferred stock 48,230,736 12,228,881 150,000 138,999 Total redeemable convertible preferred stock 104,461,636 40,743,522 $ 408,000 $ 396,593

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
Common Stock (Tables)	Dec. 31, 2023
Equity [Abstract]
Schedule of Common Stock Reserved for Future Issuance	As of December 31, 2023 and 2022, the Company’s Common Stock reserved for future issuance was as follows: As of December 31, 2023 2022 Shares available for future grants under Equity Incentive Plan 3,526,392 1,570,353 Outstanding stock options 9,630,623 5,036,946 Performance-based restricted stock units 2,964,072 — Outstanding restricted stock units 2,166,016 1,107,213 Options assumed upon ValenzaBio acquisition 938,440 — ESPP Shares available for future grants 875,836 — Redeemable convertible preferred stock — 40,743,522 Total shares reserved for future issuance 20,101,379 48,458,034

Equity Incentive Plan (Tables)

Equity Incentive Plan (Tables)	12 Months Ended
Equity Incentive Plan (Tables)	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Summary of Stock Option Activity	A summary of option activity under the 2020 Plan and 2023 plan is as follows: Number of Weighted- Weighted- Aggregate Outstanding at December 31, 2022 5,036,946 $ 4.7872 9.5 $ 5,488 Options granted 6,196,917 $ 14.9001 Options exercised (330,506) $ 5.1507 Options expired (10,653) $ 18.0000 Options forfeited (1,262,081) $ 10.9333 Outstanding at December 31, 2023 9,630,623 $ 10.4619 9 $ 12,007 Exercisable at December 31, 2023 1,661,322 $ 4.4577 8.1 $ 5,226 Vested and expected to vest at December 31, 2023 9,630,623 $ 10.4619 9 $ 12,007
Summary of Restricted Stock Unit Activity	A summary of unvested RSU activity is presented in the following table: Number of RSUs Weighted-Average Grant Date Fair Value Unvested at December 31, 2022 1,107,213 $ 5.42 Granted 1,725,168 28.15 Vested (640,416) 6.65 Forfeited (25,949) 26.97 Unvested at December 31, 2023 2,166,016 $ 22.90
Summary of Performance Share Activity	A summary of PSU activity based on the target number of shares is presented in the following table: Number of PSUs Weighted-Average Grant Date Fair Value* Outstanding at December 31, 2022 — $ — Granted 3,135,104 27.43 Vested — — Forfeited (171,032) 27.43 Outstanding at December 31, 2023 2,964,072 $ 27.43 *The grant date fair value is based only on the PSUs with market conditions and does not factor in any performance conditions.
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions	The Company used the following assumptions to estimate fair value of each option at the grant date for the years ended December 31, 2023, 2022 and 2021: Year Ended December 31, 2023 2022 2021 Expected volatility 85.17% - 94.74% 96.33% - 102.81% 99.97% - 100.78% Expected dividend yield 0 % 0 % 0 % Expected term (in years) 5.77 - 6.08 years 5.88 - 6.08 years 5.93 - 6.06 years Risk-free interest rate 3.30% - 4.80% 1.69% - 3.96% 0.87% - 0.97%
Share-Based Payment Arrangement, Expensed and Capitalized, Amount	The following table presents the classification of stock-based compensation expense related to awards granted to employees and non-employees (in thousands): Year Ended December 31, 2023 2022 2021 Research and development expenses $ 12,652 $ 1,373 $ 214 General and administrative expenses 34,666 2,679 19 Total stock-based compensation expense $ 47,318 $ 4,052 $ 233 The stock-based compensation expense relates to the following equity-based awards: Year Ended December 31, 2023 2022 2021 Restricted stock units $ 11,726 $ — $ — Performance-based restricted stock units 12,109 — — Stock options 23,281 2,035 233 ESPP 202 — — Restricted stock awards — 2,017 — Total stock-based compensation expense $ 47,318 $ 4,052 $ 233

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Year Ended December 31, 2023 2022 2021 Numerator: Net loss $ (381,641) $ (64,772) $ (41,839) Denominator: Weighted average common shares outstanding 70,647,093 3,271,978 2,843,305 Less: Weighted-average common shares subject to repurchase (397,513) (1,714,444) (2,155,907) Weighted-average common shares outstanding, basic and diluted 70,249,580 1,557,534 687,398 Net loss per share attributable to common stockholders, basic and diluted $ (5.43) $ (41.59) $ (60.87)
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been antidilutive: As of December 31, 2023 2022 2021 Outstanding options to purchase common stock 9,630,623 5,036,946 481,994 Unvested RSUs outstanding 2,166,016 1,107,213 — Outstanding options to purchase common stock assumed upon the ValenzaBio acquisition 938,440 — — Common stock subject to repurchase 207,060 562,032 1,774,841 ESPP 87,356 — — Redeemable convertible preferred stock — 40,743,522 16,285,718 Total 13,029,495 47,449,713 18,542,553

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2023
Income Tax Disclosure [Abstract]
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 was as follows: Year Ended December 31, 2023 2022 2021 Income tax computed at federal statutory rate 21.00 % 21.00 % 21 % State taxes 0.07 0.71 0.26 Other permanent differences (1.03) (0.43) (0.11) Research credits 1.12 1.40 0.19 Change in valuation allowance (14.38) (22.68) (21.34) IPR&D (6.78 %) — % — % Effective income tax rate — % — % — %
Schedule of Deferred Tax Assets	Significant components of the deferred tax assets and liabilities were as follows (in thousands): Year Ended December 31, 2023 2022 Deferred Tax Assets: Net operating loss carry forwards $ 19,640 $ 6,203 Capitalized R&E expenditures 52,911 10,814 Intangibles 14,439 4,785 Research credits 6,898 1,259 Lease liability 298 — Other 4,782 676 Total deferred tax assets 98,968 23,737 Less: Valuation allowance (98,716) (23,737) Net deferred tax assets $ 252 $ — Right-of-use asset (ROU) $ (252) $ — Net deferred tax liability $ (252) $ — Total net deferred tax assets $ — $ —
Summary of Operating Loss Carryforwards	The following table sets forth the Company’s federal and state net operating loss carryforwards and tax credits as of December 31, 2023 (dollars in thousands): Amount Begin to Expire Net operating losses, Federal $ 92,703 Do not expire Net operating losses, State $ 6,820 2041 Tax credits, Federal $ 8,320 2041 Tax credits, California $ 1,110 Do not expire
Summary of Tax Credit Carryforwards	The following table sets forth the Company’s federal and state net operating loss carryforwards and tax credits as of December 31, 2023 (dollars in thousands): Amount Begin to Expire Net operating losses, Federal $ 92,703 Do not expire Net operating losses, State $ 6,820 2041 Tax credits, Federal $ 8,320 2041 Tax credits, California $ 1,110 Do not expire
Summary of Uncertain Tax Positions	A reconciliation of the beginning and ending balances of the unrecognized tax benefits during the year ended December 31, 2023, 2022 and 2021 are as follows (in thousands) Year Ended December 31, 2023 2022 2021 Beginning balance $ 516 $ 48 $ — Increase in tax positions in the current period 1,600 468 48 Additions for tax positions of prior years 233 — — Ending balance $ 2,348 $ 516 $ 48

Description of Business, Orga_2

Description of Business, Organization and Liquidity (Details) $ / shares in Units, $ in Thousands				12 Months Ended
	May 09, 2023 USD ($) $ / shares shares	Apr. 25, 2023	Jan. 04, 2023 USD ($) shares	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jul. 31, 2020 $ / shares
Subsidiary, Sale of Stock [Line Items]
Reverse stock split, conversion ratio		0.5071
Sale of stock, price (in dollars per share) \| $ / shares							$ 0.00002
Underwriting discounts, commissions and offering costs				$ 47,354
Temporary equity, convertible, conversion ratio	100%			100%
Net losses				$ 381,641	$ 64,772	$ 41,839
Research and development				355,886	55,632	38,230
Payments to acquire in-process research and development				10,000	0	25,000
Accumulated deficit				488,719	107,078
Cash used in operating activities				169,705	$ 61,520	$ 4,979
Cash, cash equivalents and short-term marketable securities				721,300
Pierre Fabre
Subsidiary, Sale of Stock [Line Items]
Payments to acquire in-process research and development			$ 10,000	10,000
ValenzaBio Asset Acquisition
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock in connection with ValenzaBio acquisition (in shares) \| shares			2,013,673
Research and development			$ 123,100	$ 123,100
ValenzaBio Asset Acquisition \| Common Class A
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock in connection with ValenzaBio acquisition (in shares) \| shares			18,885,731
IPO
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares) \| shares	34,500,000
Sale of stock, price (in dollars per share) \| $ / shares	$ 18
Gross proceeds received on transaction	$ 621,000
Net proceeds received on transaction	573,600
Underwriting discounts, commissions and offering costs	$ 47,400
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares) \| shares	4,500,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details)	12 Months Ended
Summary of Significant Accounting Policies (Details)	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)
Debt Securities, Available-for-Sale [Line Items]
Number of operating segments \| segment	1
Total cash equivalents and marketable securities	$ 711,588,000	$ 285,733,000
Acquisition transaction costs	0	1,121,000
Deferred offering costs	$ 0	$ 200,000
Cash \| Financial Institution Risk \| Cash Balances Exceeding Federal Insurance Limits
Debt Securities, Available-for-Sale [Line Items]
Concentration risk, percentage	100%	100%
Money market funds (included in cash and cash equivalents)
Debt Securities, Available-for-Sale [Line Items]
Total cash equivalents and marketable securities	$ 23,205,000	$ 238,223,000

ValenzaBio Acquisition - Narrat

ValenzaBio Acquisition - Narrative (Details)		3 Months Ended	12 Months Ended
ValenzaBio Acquisition - Narrative (Details)	Jan. 04, 2023 USD ($) shares	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Asset Acquisition [Line Items]
Expense related to acquired in-process research and development assets			$ 133,057,000	$ 0	$ 25,000,000
Research and development			355,886,000	55,632,000	38,230,000
Severance payable, current			300,000
Payments to acquire in-process research and development			$ 10,000,000	$ 0	$ 25,000,000
Exercisable			8 years 1 month 6 days
Minimum
Asset Acquisition [Line Items]
Severance payment obligation period	3 months
Maximum
Asset Acquisition [Line Items]
Severance payment obligation period	18 months
Unvested Equity Awards
Asset Acquisition [Line Items]
Separately recognized expenses		$ 900,000
Severance Payment Obligation
Asset Acquisition [Line Items]
Liabilities recognized	$ 5,100,000
Severance Payment Obligation \| Discount rate
Asset Acquisition [Line Items]
Measurement input	8%
Research and Development Expense \| Assumed Options
Asset Acquisition [Line Items]
Separately recognized expenses		3,100,000
Research and Development Expense \| Severance Payment Obligation
Asset Acquisition [Line Items]
Separately recognized expenses		2,500,000
Research and Development Expense \| Severance Payment Obligation Accretion
Asset Acquisition [Line Items]
Separately recognized expenses			$ 100,000
General and Administrative Expense \| Assumed Options
Asset Acquisition [Line Items]
Separately recognized expenses		1,800,000
General and Administrative Expense \| Severance Payment Obligation
Asset Acquisition [Line Items]
Separately recognized expenses		2,400,000
Non-Accredited Investor \| General and Administrative Expense
Asset Acquisition [Line Items]
Separately recognized expenses		8,387
Former ValenzaBio Employee \| General and Administrative Expense
Asset Acquisition [Line Items]
Separately recognized expenses		$ 30,000
Pierre Fabre
Asset Acquisition [Line Items]
Payments to acquire in-process research and development	$ 10,000,000		10,000,000
ValenzaBio Asset Acquisition
Asset Acquisition [Line Items]
Issuance of common stock in connection with ValenzaBio acquisition (in shares) \| shares	2,013,673
Shares issued, withholding period	12 months
Asset acquisition payment	$ 7,663
Contingent consideration	100,000
Transaction cost, net	$ 1,200,000
Options exercisable (in shares) \| shares	1,249,811
Options exchange ratio	0.008027010
Research and development	$ 123,100,000		$ 123,100,000
Exercisable	12 months
ValenzaBio Asset Acquisition \| Common Class A
Asset Acquisition [Line Items]
Issuance of common stock in connection with ValenzaBio acquisition (in shares) \| shares	18,885,731
ValenzaBio Asset Acquisition \| lonigutamab
Asset Acquisition [Line Items]
Expense related to acquired in-process research and development assets	$ 114,800,000
ValenzaBio Asset Acquisition \| SLRN-517
Asset Acquisition [Line Items]
Expense related to acquired in-process research and development assets	$ 8,200,000

ValenzaBio Acquisition - Schedu

ValenzaBio Acquisition - Schedule of Total Purchase Consideration (Details) - ValenzaBio Asset Acquisition	Jan. 04, 2023 USD ($) $ / shares shares
Asset Acquisition [Line Items]
Issued common stock	$ 128,735,000
Transaction costs	1,271,000
Cash	7,663
Total	$ 130,014,000
Shares issued (in dollars per share) \| $ / shares	$ 6.86
Issuance of common stock in connection with ValenzaBio acquisition (in shares) \| shares	2,013,673
Contingent consideration	$ 100,000

ValenzaBio Acquisition - Sche_2

ValenzaBio Acquisition - Schedule of Allocation of Purchase Consideration (Details) - ValenzaBio Asset Acquisition $ in Thousands	Jan. 04, 2023 USD ($)
Asset Acquisition [Line Items]
Cash	$ 11,369
Prepaid expenses and other current assets	2,074
In-process research and development assets	123,057
Accounts payable	(1,628)
Accrued research and development expenses	(4,805)
Accrued compensation and other current liabilities	(53)
Total net asset acquired	$ 130,014

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Financial Instruments Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Assets:
Debt securities, available-for-sale	$ 711,588	$ 285,733
Total fair value of assets	711,588	285,733
Liabilities:
Derivative tranche liability	0	10,291
Total fair value of liabilities		10,291
Cash and cash equivalents
Assets:
Debt securities, available-for-sale	208,359	238,223
Money market funds (included in cash and cash equivalents)
Assets:
Debt securities, available-for-sale	23,205	238,223
U.S. Government bonds
Assets:
Debt securities, available-for-sale		25,459
U.S. Treasury bills
Assets:
Debt securities, available-for-sale	525,353	11,404
U.S. Treasury bills \| Cash and cash equivalents
Assets:
Debt securities, available-for-sale	146,497
Corporate debt obligations
Assets:
Debt securities, available-for-sale	135,284	2,141
Corporate debt obligations \| Cash and cash equivalents
Assets:
Debt securities, available-for-sale	23,313
Federal agency obligations
Assets:
Debt securities, available-for-sale	27,746	8,506
Federal agency obligations \| Cash and cash equivalents
Assets:
Debt securities, available-for-sale	15,344
Level 1
Assets:
Total fair value of assets	23,205	249,627
Liabilities:
Derivative tranche liability		0
Total fair value of liabilities		0
Level 1 \| Money market funds (included in cash and cash equivalents)
Assets:
Debt securities, available-for-sale	23,205	238,223
Level 1 \| U.S. Government bonds
Assets:
Debt securities, available-for-sale		0
Level 1 \| U.S. Treasury bills
Assets:
Debt securities, available-for-sale	0	11,404
Level 1 \| Corporate debt obligations
Assets:
Debt securities, available-for-sale	0	0
Level 1 \| Federal agency obligations
Assets:
Debt securities, available-for-sale	0	0
Level 2
Assets:
Total fair value of assets	688,383	36,106
Liabilities:
Derivative tranche liability		0
Total fair value of liabilities		0
Level 2 \| Money market funds (included in cash and cash equivalents)
Assets:
Debt securities, available-for-sale	0	0
Level 2 \| U.S. Government bonds
Assets:
Debt securities, available-for-sale		25,459
Level 2 \| U.S. Treasury bills
Assets:
Debt securities, available-for-sale	525,353	0
Level 2 \| Corporate debt obligations
Assets:
Debt securities, available-for-sale	135,284	2,141
Level 2 \| Federal agency obligations
Assets:
Debt securities, available-for-sale	27,746	8,506
Level 3
Assets:
Total fair value of assets	0	0
Liabilities:
Derivative tranche liability		10,291
Total fair value of liabilities		10,291
Level 3 \| Money market funds (included in cash and cash equivalents)
Assets:
Debt securities, available-for-sale	0	0
Level 3 \| U.S. Government bonds
Assets:
Debt securities, available-for-sale		0
Level 3 \| U.S. Treasury bills
Assets:
Debt securities, available-for-sale	0	0
Level 3 \| Corporate debt obligations
Assets:
Debt securities, available-for-sale	0	0
Level 3 \| Federal agency obligations
Assets:
Debt securities, available-for-sale	$ 0	$ 0

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Cash and Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 711,588	$ 285,733
Cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	208,359	238,223
Short-term marketable securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 503,229	$ 47,510

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Changes in Level 3 Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance as of January 1st	$ 10,291	$ 0
Fair value of derivative tranche liability upon issuance	0	10,778
Change in fair value	$ (10,291)	(487)
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Change in fair value of derivative tranche liability
Balance as of December 31st	$ 0	$ 10,291

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) $ / shares in Units, $ in Millions	May 09, 2023 $ / shares	Dec. 31, 2022	Sep. 09, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability \| $			$ 10.8
Derivative Liability, Statement of Financial Position [Extensible Enumeration]			Derivative tranche liability
Level 3 \| Fair value of Series C preferred stock share
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input	12.2661	12.2661
IPO
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Share price (in dollars per share) \| $ / shares	$ 18

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Significant Assumptions Used to Estimate Fair Value (Details)	Dec. 31, 2023	May 09, 2023	Dec. 31, 2022	Sep. 30, 2022
Probability of achieving specified conditions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input	0.90
Probability of achieving specified conditions \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input			0.80
Fair value of Series C preferred stock share \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input		12.2661	12.2661
Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input				0.25
Discount rate \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative liability, measurement input			0.25

Available-For-Sale Marketable_3

Available-For-Sale Marketable Securities - Schedule of Available-for-Sale Marketable Securities (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	$ 711,426,000	$ 285,819,000
Total Unrealized Gain	204,000	0
Total Unrealized Loss	(42,000)	(86,000)
Total Estimated Fair Value	711,588,000	285,733,000
Cash and cash equivalents
Debt Securities, Available-for-Sale [Line Items]
Total Estimated Fair Value	208,359,000	238,223,000
Money market funds (included in cash and cash equivalents)
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	23,205,000	238,223,000
Total Unrealized Gain	0
Total Unrealized Loss	0	0
Total Estimated Fair Value	23,205,000	238,223,000
U.S. Government bonds
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost		25,506,000
Total Unrealized Loss		(47,000)
Total Estimated Fair Value		25,459,000
U.S. Treasury obligations
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	525,198,000	11,430,000
Total Unrealized Gain	156,000
Total Unrealized Loss	(1,000)	(26,000)
Total Estimated Fair Value	525,353,000	11,404,000
U.S. Treasury obligations \| Cash and cash equivalents
Debt Securities, Available-for-Sale [Line Items]
Total Estimated Fair Value	146,497,000
Corporate debt obligations
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	135,288,000	2,145,000
Total Unrealized Gain	36,000
Total Unrealized Loss	(40,000)	(4,000)
Total Estimated Fair Value	135,284,000	2,141,000
Corporate debt obligations \| Cash and cash equivalents
Debt Securities, Available-for-Sale [Line Items]
Total Estimated Fair Value	23,313,000
Federal agency obligations
Debt Securities, Available-for-Sale [Line Items]
Total Amortized Cost	27,735,000	8,515,000
Total Unrealized Gain	12,000
Total Unrealized Loss	(1,000)	(9,000)
Total Estimated Fair Value	27,746,000	$ 8,506,000
Federal agency obligations \| Cash and cash equivalents
Debt Securities, Available-for-Sale [Line Items]
Total Estimated Fair Value	$ 15,344,000

Available-For-Sale Marketable_4

Available-For-Sale Marketable Securities - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Allowance for credit loss	$ 0
Accrued interest receivable	$ 800,000	$ 100,000
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Current, Statement of Financial Position [Extensible Enumeration]	Prepaid expenses and other current assets	Prepaid expenses and other current assets
Accrued interest writeoff	$ 0	$ 0	$ 0
Debt securities, available-for-sale, term	1 year

Consolidated Balance Sheet Co_3

Consolidated Balance Sheet Components - Schedule of Prepaid and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Prepaid research and development expenses	$ 8,184	$ 682
Value-Added Tax (VAT) receivable	3,985	0
Prepaid insurance and other current assets	1,712	86
Interest receivable	764	138
Prepaid other services	667	288
Research and development credit receivable	0	250
Total	$ 15,312	$ 1,444

Consolidated Balance Sheet Co_4

Consolidated Balance Sheet Components - Schedule of Prepaid and Other Noncurrent Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Prepaid research and development expenses, non-current	$ 2,644	$ 1,964
Security deposits	34	0
Acquisition transaction costs	0	1,121
Deferred IPO offering costs	0	774
Total	$ 2,678	$ 3,859

Consolidated Balance Sheet Co_5

Consolidated Balance Sheet Components - Property, Plant and Equipment (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 2,294,000
Less: accumulated depreciation and amortization	(115,000)
Property, plant and equipment, net	2,179,000	$ 0
Construction in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	1,460,000
Computer and other equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	407,000
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	306,000
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 121,000

Consolidated Balance Sheet Co_6

Consolidated Balance Sheet Components - Accrued Research and Development Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued clinical manufacturing expenses	$ 22,232	$ 1,292
Accrued clinical expenses	13,204	4,425
Accrued research and development expenses	$ 35,436	$ 5,717

Consolidated Balance Sheet Co_7

Consolidated Balance Sheet Components - Schedule of Accrued Compensation and Other Current Liabilities (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued compensation	$ 5,417,000	$ 3,068,000
Accrued professional services fees	1,099,000	808,000
Other accrued expenses and current liabilities	317,000	361,000
Total	6,833,000	4,237,000
Deferred offering costs	$ 0	$ 200,000

Significant Agreements (Details

Significant Agreements (Details) - USD ($)				1 Months Ended	12 Months Ended
Significant Agreements (Details) - USD ($)	Jan. 04, 2023	Aug. 09, 2021	Mar. 25, 2021	Nov. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Oct. 31, 2021	Sep. 30, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development					$ 355,886,000	$ 55,632,000	$ 38,230,000
Affibody \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate milestone payments								$ 22,000,000	$ 3,000,000
Maximum aggregate milestone payments		$ 280,000,000
Payment due prior to milestone		$ 30,000,000
Aggregate milestone payments, period		10 years
Research and development				$ 15,000,000			$ 25,000,000
Pierre Fabre \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate milestone payments			$ 10,000,000
Aggregate milestone payments, period			10 years
Research and development					10,000,000
One-time payment			$ 31,000,000
One-time payment, period			30 days
Termination period			9 months
Probable milestone payments					0
Pierre Fabre \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Development and Regulatory Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments			$ 99,500,000
Pierre Fabre \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Commercial Sales Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments			$ 390,000,000
Novelty Nobility \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate milestone payments, period	10 years
Probable milestone payments					$ 0
Contract termination, period	30 days
Novelty Nobility \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Development and Regulatory Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments	$ 44,300,000
Novelty Nobility \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Commercial Sales Milestone Payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Maximum aggregate milestone payments	$ 682,000,000

Commitments and Contingent Li_3

Commitments and Contingent Liabilities - Narrative (Details)	1 Months Ended			12 Months Ended
	Nov. 30, 2023 USD ($)	Jul. 31, 2023 USD ($) ft²	Jan. 31, 2023 USD ($) ft²	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Other Commitments [Line Items]
Research and development				$ 355,886,000	$ 55,632,000	$ 38,230,000
Unrecorded unconditional purchase obligation				142,344,000	100,000
Unrecorded unconditional purchase obligation, accrued charges				0	0
Square feet leased (in square feet) \| ft²			10,012
Term of contract			65 months
Renewal term			3 years
Monthly payments			$ 30,500
Annual rent increase			3%
Rent abatement, term			6 months
Security deposit				34,000
Operating lease liability, non-current			$ 1,300,000	1,194,000	0
Operating lease right-of-use asset				1,195,000	$ 0
Office space leased (in square feet) \| ft²		22,365
Term of contract		60 months
Renewal term		3 years
Monthly payments		$ 150,000
Annual rent increase		3.50%
Operating lease costs				300,000
Short-term lease, cost				$ 100,000
Weighted average remaining lease term				56 months
Discount rate				12%
Lease liability measurement (less than)				$ 100,000
Affibody \| Collaborative Arrangement, Transaction with Party to Collaborative Arrangement
Other Commitments [Line Items]
Research and development	$ 15,000,000					$ 25,000,000

Commitments and Contingent Li_4

Commitments and Contingent Liabilities - Schedule of Non-cancellable Purchase Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	$ 67,567
2025	53,686
2026	20,985
2027 and thereafter	106
Total	$ 142,344	$ 100

Commitments and Contingent Li_5

Commitments and Contingent Liabilities - Summary of Maturity Analysis of Operating Lease Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Jan. 31, 2023	Dec. 31, 2022
Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract]
2024	$ 375
2025	386
2026	398
2027	409
2028	280
Total future lease payments	1,848
Less imputed interest	(434)
Total operating lease liability balance	1,414
Less current portion of lease liability (included in accrued compensation and other current liabilities)	$ (220)
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued compensation and other current liabilities
Operating lease liability, non-current	$ 1,194	$ 1,300	$ 0

Redeemable Convertible Prefer_3

Redeemable Convertible Preferred Stock - Narrative (Details)			1 Months Ended			12 Months Ended
	Jun. 30, 2023 shares	May 09, 2023 $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Feb. 28, 2022 USD ($) $ / shares shares	Oct. 31, 2021 USD ($) day $ / shares shares	Dec. 31, 2023 USD ($)	Dec. 31, 2022 $ / shares shares	Dec. 31, 2021 shares	Sep. 30, 2023 $ / shares	Oct. 31, 2020 $ / shares
Class of Stock [Line Items]
Threshold trading days \| day					15
Temporary equity, convertible, conversion ratio		100%				100%
Temporary equity, conversion event proceeds, minimum threshold						$ 3,000,000
Series B Convertible Preferred Stock
Class of Stock [Line Items]
Issuance of convertible preferred stock (in shares) \| shares				12,228,923	12,228,923		12,228,923	12,228,923
Shares issued, price per share (in dollars per share) \| $ / shares				$ 10.2217	$ 10.2217
Issuance of redeemable convertible preferred stock, gross				$ 125,000,000	$ 125,000,000
Stock issuance costs				$ 100,000	$ 300,000
Dividend rate						8%
Series C Convertible Preferred Stock
Class of Stock [Line Items]
Issuance of convertible preferred stock (in shares) \| shares	12,228,881	12,228,881	12,228,881				12,228,881
Shares issued, price per share (in dollars per share) \| $ / shares		$ 12.2661	$ 12.2661				$ 12.2661		$ 12.2661
Issuance of redeemable convertible preferred stock, gross			$ 150,000,000
Stock issuance costs			$ 200,000
Temporary equity, convertible, conversion ratio	1,000%
Dividend rate						8%
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Shares issued, price per share (in dollars per share) \| $ / shares										$ 1.9720
Dividend rate						8%

Redeemable Convertible Prefer_4

Redeemable Convertible Preferred Stock - Schedule of Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Shares Authorized (in shares)	0	104,461,636
Shares Issued (in shares)	0	40,743,522
Shares Outstanding (in shares)	0	40,743,522	16,285,718	4,056,795
Aggregate Liquidation Preference		$ 408,000
Net Carrying Value	$ 0	$ 396,593	$ 132,620	$ 7,916
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Shares Authorized (in shares)		8,000,000
Shares Issued (in shares)		4,056,795
Shares Outstanding (in shares)		4,056,795
Aggregate Liquidation Preference		$ 8,000
Net Carrying Value		$ 7,916
Series B Convertible Preferred Stock
Class of Stock [Line Items]
Shares Authorized (in shares)		48,230,900
Shares Issued (in shares)		24,457,846
Shares Outstanding (in shares)		24,457,846
Aggregate Liquidation Preference		$ 250,000
Net Carrying Value		$ 249,678
Series C Convertible Preferred Stock
Class of Stock [Line Items]
Shares Authorized (in shares)		48,230,736
Shares Issued (in shares)		12,228,881
Shares Outstanding (in shares)		12,228,881
Aggregate Liquidation Preference		$ 150,000
Net Carrying Value		$ 138,999

Derivative Tranche Liability (D

Derivative Tranche Liability (Details) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Jun. 30, 2023 shares	May 09, 2023 USD ($) $ / shares shares	Sep. 30, 2022 $ / shares shares	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($)	Sep. 30, 2023 $ / shares
Derivative [Line Items]
Derivative tranche liability				$ 0	$ 10,291
Change in fair value of derivative tranche liability				$ 10,291	$ 487	$ 0
Probability of achieving specified conditions
Derivative [Line Items]
Derivative liability, measurement input				0.90
Discount rate
Derivative [Line Items]
Derivative liability, measurement input			0.25
Forward Contracts
Derivative [Line Items]
Derivative tranche liability		$ 10,800
Series C Convertible Preferred Stock
Derivative [Line Items]
Issuance of convertible preferred stock (in shares) \| shares	12,228,881	12,228,881	12,228,881		12,228,881
Shares issued, price per share (in dollars per share) \| $ / shares		$ 12.2661	$ 12.2661		$ 12.2661		$ 12.2661
Derivative tranche liability					$ 10,778

Common Stock - Narrative (Detai

Common Stock - Narrative (Details) - $ / shares	1 Months Ended		12 Months Ended
Common Stock - Narrative (Details) - $ / shares	Dec. 31, 2022	Jul. 31, 2020	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Stock issued during period, issued for services (in shares)		2,839,749
Sale of stock, price (in dollars per share)		$ 0.00002
Restricted stock awards
Class of Stock [Line Items]
Vesting period		48 months
Forfeited in period (in shares)	591,613
Shares unvested (in shares)	562,032		207,060	562,032
Vested (in shares)			354,972	621,196

Common Stock - Schedule of Comm

Common Stock - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	20,101,379	48,458,034
Shares available for future grants under Equity Incentive Plan
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	3,526,392	1,570,353
Outstanding stock options
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	9,630,623	5,036,946
Outstanding stock options \| Options assumed upon ValenzaBio acquisition
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	938,440	0
Performance-based restricted stock units
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	2,964,072	0
Outstanding restricted stock units
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	2,166,016	1,107,213
ESPP Shares available for future grants
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	875,836	0
Redeemable convertible preferred stock
Class of Stock [Line Items]
Total shares reserved for future issuance (in shares)	0	40,743,522

Equity Incentive Plan - Narrati

Equity Incentive Plan - Narrative (Details) - USD ($)						1 Months Ended			12 Months Ended
Equity Incentive Plan - Narrative (Details) - USD ($)	Aug. 16, 2023	May 09, 2023	May 04, 2023	Mar. 23, 2023	Jan. 04, 2023	Aug. 31, 2023	Apr. 30, 2023	Jul. 31, 2020	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total shares reserved for future issuance (in shares)									20,101,379	48,458,034
Common stock, issued (in shares)									97,865,890	97,865,890
Common stock, outstanding (in shares)									2,767,359	2,767,359
Share-based and cash-based compensation, maximum			$ 750,000
Fair value of shares vested										$ 10,600,000
Weighted-average grant date fair value, grants in period (in dollars per share)										$ 8.8732
Options granted (in shares)									6,196,917
Exercisable (in dollars per share)									$ 4.4577
Exercises in period (in shares)									330,506
Options expired (in dollars per share)									$ 18
Total stock-based compensation expense									$ 47,318,000	$ 4,052,000	$ 233,000
Accrued compensation and other current liabilities									$ 6,833,000	4,237,000
Issuance of common stock under the employee stock purchase plan (in shares)									24,164
Issuance of common stock under the employee stock purchase plan									$ 149,000
Research and Development Expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense									12,652,000	1,373,000	214,000
General and Administrative Expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense									$ 34,666,000	$ 2,679,000	19,000
Nonemployee
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based and cash-based compensation, maximum			$ 1,000,000
Stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total shares reserved for future issuance (in shares)									9,630,623	5,036,946
Expiration period									10 years
Total stock-based compensation expense									$ 23,281,000	$ 2,035,000	$ 233,000
Expected dividend yield									0%	0%	0%
ESPP Shares available for future grants
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total shares reserved for future issuance (in shares)									875,836	0
Purchase price of common stock							85%
Number of shares authorized (in shares)							900,000
Percentage of eligible compensation for payroll deductions to purchase stock							15%
Annual increase, period							10 years
Annual increase as percentage of shares outstanding							1%
Maximum number of shares available over award term							2,700,000
Total stock-based compensation expense									$ 202,000	$ 0	$ 0
Accrued compensation and other current liabilities									$ 100,000
Unvested RSUs outstanding
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total shares reserved for future issuance (in shares)									2,166,016	1,107,213
Vesting period	4 years
Total stock-based compensation expense									$ 11,726,000	$ 0	0
Shares granted (in shares)	1,725,168								1,725,168	1,107,213
Accelerated vesting of awards (in shares)				138,401
Fair value				$ 8,000,000
Vested (in shares)									640,416
Shares unvested (in shares)									2,166,016	1,107,213
Granted (in dollars per share)									$ 28.15
Unvested RSUs outstanding \| August 16, 2023 Awards
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense									$ 5,800,000
Unvested RSUs outstanding \| Tranche One
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting rights, percentage	25%
Unvested RSUs outstanding \| Tranche Two
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting rights, percentage	25%
Unvested RSUs outstanding \| Tranche Three
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting rights, percentage	25%
Unvested RSUs outstanding \| Tranche Four
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Award vesting rights, percentage	25%
Unvested RSUs outstanding \| Chief Executive Officer
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense		$ 5,500,000
Vested (in shares)		640,416
Issued (in shares)		303,237
Withheld for tax withholding obligation (in shares)		337,179
Withheld for tax withholding obligation		$ 8,300,000
Performance-based restricted stock units
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total shares reserved for future issuance (in shares)									2,964,072	0
Expiration period									3 years
Total stock-based compensation expense									$ 12,109,000	$ 0	0
Shares granted (in shares)									3,135,104
Vested (in shares)									0
Shares unvested (in shares)									2,964,072	0
Target number of shares (in shares)						3,135,104
Target number of shares, percentage						150%
Share price (in dollars per share)									$ 26,970,000
Expected volatility									87.71%
Risk-free interest rate									4.47%
Expected dividend yield									0%
Granted (in dollars per share)									$ 27.43
Weighted-average recognition period									2 years 3 months 18 days
Unrecognized stock-based compensation expense									$ 65,400,000
Unrecognized stock-based compensation expense, maximum									86,600,000
Restricted stock awards
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Vesting period								48 months
Total stock-based compensation expense									$ 0	$ 2,017,000	$ 0
Vested (in shares)									354,972	621,196
Shares unvested (in shares)									207,060	562,032
2023 Equity Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total shares reserved for future issuance (in shares)			12,000,000						3,526,392,000,000
Percentage of outstanding stock maximum			500%
Vesting period			4 years
2023 Equity Incentive Plan \| Stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issuable (in shares)			56,762,538
2023 Equity Incentive Plan \| Stock options \| Stockholder, 10% or More
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expiration period			5 years
2023 Equity Incentive Plan \| Stock options \| Minimum \| Stockholder, 10% or More
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Purchase price of common stock			110%
2020 Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock, issued (in shares)			6,920,846
Common stock, outstanding (in shares)			6,920,846
Options assumed upon ValenzaBio acquisition
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Options granted (in shares)					1,249,811
Exercisable (in dollars per share)					$ 3.6736
Exercises in period (in shares)									311,371
Options expired (in dollars per share)									$ 2.4921
Unrecognized stock-based compensation expense									$ 65,500,000
Options assumed upon ValenzaBio acquisition \| ValenzaBio Asset Acquisition
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense									4,900,000
Options assumed upon ValenzaBio acquisition \| ValenzaBio Asset Acquisition \| Research and Development Expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense									3,100,000
Options assumed upon ValenzaBio acquisition \| ValenzaBio Asset Acquisition \| General and Administrative Expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense									$ 1,800,000
Options assumed upon ValenzaBio acquisition \| Stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total shares reserved for future issuance (in shares)									938,440	0
Weighted-average recognition period									3 years 2 months 12 days
Options assumed upon ValenzaBio acquisition \| Stock options \| ValenzaBio Asset Acquisition
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense					$ 4,900,000
Options assumed upon ValenzaBio acquisition \| Unvested RSUs outstanding
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unrecognized stock-based compensation expense									$ 41,700,000
Options assumed upon ValenzaBio acquisition \| Restricted stock awards \| ValenzaBio Asset Acquisition
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense					$ 900,000

Equity Incentive Plan - Summary

Equity Incentive Plan - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Options
Outstanding, beginning balance (in shares)	5,036,946
Options granted (in shares)	6,196,917
Options exercised (in shares)	(330,506)
Options expired (in shares)	(10,653)
Options forfeited (in shares)	(1,262,081)
Outstanding, ending balance (in shares)	9,630,623	5,036,946
Exercisable (in shares)	1,661,322
Vested and expected to vest (in shares)	9,630,623
Weighted- Average Exercise Price Per Share
Outstanding, beginning balance (in dollars per share)	$ 4.7872
Options granted (in dollars per share)	14.9001
Options exercised (in dollars per share)	5.1507
Options expired (in dollars per share)	18
Options forfeited (in dollars per share)	10.9333
Outstanding, ending balance (in dollars per share)	10.4619	$ 4.7872
Exercisable (in dollars per share)	4.4577
Vested and expected to vest (in dollars per share)	$ 10.4619
Weighted-Average Remaining Contractual Term
Outstanding	9 years	9 years 6 months
Exercisable	8 years 1 month 6 days
Vested and expected to vest	9 years
Aggregate Intrinsic Value
Outstanding	$ 12,007	$ 5,488
Exercisable	5,226
Vested and expected to vest	$ 12,007

Equity Incentive Plan - Summa_2

Equity Incentive Plan - Summary of Restricted Stock Unit Activity (Details) - Restricted stock units - $ / shares		12 Months Ended
	Aug. 16, 2023	Dec. 31, 2023	Dec. 31, 2022
Number of Shares
Outstanding at beginning of period (in shares)		1,107,213
Shares granted (in shares)	1,725,168	1,725,168	1,107,213
Vested (in shares)		(640,416)
Forfeited (in shares)		(25,949)
Outstanding at end of period (in shares)		2,166,016	1,107,213
Weighted-Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share)		$ 5.42
Granted (in dollars per share)		28.15
Vested (in dollars per share)		6.65
Forfeited (in dollars per share)		26.97
Outstanding at end of period (in dollars per share)		$ 22.90	$ 5.42

Equity Incentive Plan - Summa_3

Equity Incentive Plan - Summary of Performance Share Activity (Details) - Performance-based restricted stock units	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Number of Shares
Outstanding at beginning of period (in shares) \| shares	0
Shares granted (in shares) \| shares	3,135,104
Vested (in shares) \| shares	0
Forfeited (in shares) \| shares	(171,032)
Outstanding at end of period (in shares) \| shares	2,964,072
Weighted-Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) \| $ / shares	$ 0
Granted (in dollars per share) \| $ / shares	27.43
Vested (in dollars per share) \| $ / shares	0
Forfeited (in dollars per share) \| $ / shares	27.43
Outstanding at end of period (in dollars per share) \| $ / shares	$ 27.43

Equity Incentive Plan - Schedul

Equity Incentive Plan - Schedule of Valuation Assumptions (Details) - Stock options	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected volatility minimum	85.17%	96.33%	99.97%
Expected volatility maximum	94.74%	102.81%	100.78%
Expected dividend yield	0%	0%	0%
Risk-free interest rate minimum	3.30%	1.69%	0.87%
Risk-free interest rate maximum	4.80%	3.96%	0.97%
Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)	5 years 9 months 7 days	5 years 10 months 17 days	5 years 11 months 4 days
Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days	6 years 21 days

Equity Incentive Plan - Sched_2

Equity Incentive Plan - Schedule of Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	$ 47,318	$ 4,052	$ 233
Restricted stock units
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	11,726	0	0
Performance-based restricted stock units
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	12,109	0	0
Stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	23,281	2,035	233
ESPP
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	202	0	0
Restricted stock awards
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	0	2,017	0
Research and development expenses
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	12,652	1,373	214
General and administrative expenses
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	$ 34,666	$ 2,679	$ 19

Related Party Transactions (Det

Related Party Transactions (Details) $ in Thousands	12 Months Ended
Related Party Transactions (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Related Party
Related Party Transaction [Line Items]
Payment for consulting and due diligence fees	$ 10

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Schedule of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net loss	$ (381,641)	$ (64,772)	$ (41,839)
Denominator:
Weighted average common shares outstanding (in shares)	70,647,093	3,271,978	2,843,305
Less: Weighted-average common shares subject to repurchase (in shares)	(397,513)	(1,714,444)	(2,155,907)
Weighted-average common shares outstanding, basic (in shares)	70,249,580	1,557,534	687,398
Weighted-average common shares outstanding, diluted (in shares)	70,249,580	1,557,534	687,398
Net loss per share attributable to common stockholder, basic (in shares)	$ (5.43)	$ (41.59)	$ (60.87)
Net loss per share attributable to common stockholder, diluted (in shares)	$ (5.43)	$ (41.59)	$ (60.87)

Net Loss Per Share Attributab_4

Net Loss Per Share Attributable to Common Stockholders - Schedule of Outstanding Shares Of Potentially Dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	13,029,495	47,449,713	18,542,553
Outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	9,630,623	5,036,946	481,994
Outstanding stock options \| ValenzaBio Asset Acquisition
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	938,440	0	0
Unvested RSUs outstanding
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,166,016	1,107,213	0
Common stock subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	207,060	562,032	1,774,841
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	87,356	0	0
Redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	40,743,522	16,285,718

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 0	$ 0
Valuation allowance	98,716,000	23,737,000		$ 100,000
Valuation allowance, increase	75,000,000	14,700,000	$ 8,900,000
Accrued interest and penalties related to unrecognized tax benefits	$ 0	$ 0

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory rate	21%	21%	21%
State taxes	0.07%	0.71%	0.26%
Other permanent differences	(1.03%)	(0.43%)	(0.11%)
Research credits	1.12%	1.40%	0.19%
Change in valuation allowance	(14.38%)	(22.68%)	(21.34%)
IPR&D	(6.78%)	0%	0%
Effective income tax rate	0%	0%	0%

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2020
Deferred Tax Assets:
Net operating loss carry forwards	$ 19,640	$ 6,203
Capitalized R&E expenditures	52,911	10,814
Intangibles	14,439	4,785
Research credits	6,898	1,259
Lease liability	298	0
Other	4,782	676
Total deferred tax assets	98,968	23,737
Less: Valuation allowance	(98,716)	(23,737)	$ (100)
Net deferred tax assets	252	0
Right-of-use asset (ROU)	(252)	0
Net deferred tax liability	(252)	0
Total net deferred tax assets	$ 0	$ 0

Income Taxes - Summary of Opera

Income Taxes - Summary of Operating Loss Carryforwards and Tax Credit Carryforwards (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Federal
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 92,703
Tax credits	8,320
California
Operating Loss Carryforwards [Line Items]
Net operating losses	6,820
Tax credits	$ 1,110

Income Taxes - Summary of Uncer

Income Taxes - Summary of Uncertain Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 516	$ 48	$ 0
Increase in tax positions in the current period	1,600	468	48
Additions for tax positions of prior years	233	0	0
Ending balance	$ 2,348	$ 516	$ 48

Subsequent Events (Details)

Subsequent Events (Details) $ in Millions	1 Months Ended	3 Months Ended
Subsequent Events (Details) $ in Millions	Nov. 30, 2023 milligram	Mar. 31, 2024 USD ($)
Vendor Programming Error, One
Subsequent Event [Line Items]
Vendor programming error, number of milligrams \| milligram	160
Vendor programming error, period	14 days
Vendor Programming Error, Two
Subsequent Event [Line Items]
Vendor programming error, number of milligrams \| milligram	80
Vendor programming error, period	28 days
Forecast \| Subsequent Event
Subsequent Event [Line Items]
Proceeds from legal settlements \| $		$ 30
Litigation settlement, amount awarded from other party, service credit \| $		$ 5