Tourmaline Bio (TRML) 10-K 19 Mar 24 2023 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Mar. 15, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Current Fiscal Year End Date	--12-31
Document Period End Date	Dec. 31, 2023
Document Transition Report	false
Entity File Number	001-40384
Entity Registrant Name	Tourmaline Bio, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	83-2377352
Entity Address, Address Line One	27 West 24th Street
Entity Address, Address Line Two	Suite 702
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10010
City Area Code	646
Local Phone Number	481-9832
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	TRML
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 89.9
Entity Common Stock, Shares Outstanding		25,646,509
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement (the “2024 Proxy Statement”) for its 2024 Annual Meeting of Stockholders, which the Registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the Registrant’s fiscal year ended December 31, 2023, are incorporated by reference into Part III of this Annual Report on Form 10-K.
Entity Central Index Key	0001827506
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2023
Auditor Information [Abstract]
Auditor Firm ID	34
Auditor Name	Deloitte & Touche LLP
Auditor Location	Morristown, New Jersey

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 140,726	$ 8,258
Short-term investments	62,225	0
Prepaid expenses and other current assets	5,923	54
Total current assets	208,874	8,312
Property and equipment, net	85	81
Restricted cash	227	216
Operating lease right-of-use asset	362	489
Other non-current assets	747	0
Total assets	210,295	9,098
Current liabilities
Accounts payable	1,071	401
Accrued expenses and other current liabilities	3,710	800
Operating lease liability, current portion	221	162
Total current liabilities	5,002	1,363
Operating lease liability, net of current portion	194	342
Other liabilities	57	0
Total liabilities	5,253	1,705
Commitments and Contingencies (Note 13)
Series A convertible preferred stock, $0.0001 par value – no shares authorized, issued or outstanding as of December 31, 2023; 27,125,000 shares authorized, issued and outstanding as of December 31, 2022	0	27,125
Stockholders’ equity (deficit)
Series A convertible preferred stock, $0.0001 par value – no shares authorized, issued or outstanding as of December 31, 2023; 27,125,000 shares authorized, issued and outstanding as of December 31, 2022	0	0
Common stock, $0.0001 par value – 140,000,000 voting shares authorized and 20,337,571 voting shares issued and outstanding as of December 31, 2023, 10,000,000 non-voting shares authorized and no non-voting shares issued or outstanding as of December 31, 2023; 50,000,000 shares authorized and 867,499 shares issued and outstanding as of December 31, 2022	2	0
Additional paid-in capital	267,024	195
Accumulated other comprehensive income	67	0
Accumulated deficit	(62,051)	(19,927)
Total stockholders’ equity (deficit)	205,042	(19,732)
Total liabilities, convertible preferred stock and stockholders’ equity (deficit)	$ 210,295	$ 9,098

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Convertible preferred stock, par value ( usd per share)	$ 0.0001	$ 0.0001
Convertible preferred stock, shares issued (in shares)	0	27,125,000
Convertible preferred stock, shares authorized (in shares)	0	27,125,000
Convertible preferred stock, shares outstanding (in shares)	0	27,125,000
Undesignated preferred stock, par value (usd per share)	$ 0.0001	$ 0.0001
Undesignated preferred stock, shares authorized (in shares)	10,000,000	0
Undesignated preferred stock, shares outstanding (in shares)	0	0
Undesignated preferred stock, shares issued (in shares)	0	0
Common stock, par value (usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	140,000,000	50,000,000
Common stock, shares, issued (in shares)	20,337,571	867,499
Common stock, shares, outstanding (in shares)	20,337,571	867,499
Nonvoting Common Stock
Common stock, shares authorized (in shares)	10,000,000
Common stock, shares, issued (in shares)	0
Common stock, shares, outstanding (in shares)	0

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating expenses:
Research and development	$ 32,368	$ 17,526
General and administrative	13,041	2,175
Total operating expenses	45,409	19,701
Loss from operations	(45,409)	(19,701)
Other income, net	3,285	0
Net loss	$ (42,124)	$ (19,701)
Net loss per share, basic (usd per share)	$ (8.87)	$ (22.46)
Net loss per share, diluted (usd per share)	$ (8.87)	$ (22.46)
Weighted-average, common shares outstanding, basic (in shares)	4,747	877
Weighted-average, common shares outstanding, diluted (in shares)	4,747	877
Other comprehensive income
Unrealized gain on short-term investments	$ 67	$ 0
Comprehensive loss	$ (42,057)	$ (19,701)

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Units/Stock and Members'/Stockholders' (Deficit) Equity - USD ($) $ in Thousands		Total	Common Units		Common Stock		Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Series A Convertible Preferred Units	Series A Convertible Preferred Stock
Beginning balance (in shares) at Dec. 31, 2021										0	0
Beginning balance at Dec. 31, 2021										$ 0	$ 0
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series A convertible preferred units, net of issuance costs (in shares)										27,125,000
Issuance of Series A convertible preferred units, net of issuance costs										$ 27,125
Conversion of convertible preferred stock to common stock in connection with reverse merger (in shares)										27,125,000	(27,125,000)
Conversion of convertible preferred stock to common stock in connection with reverse merger										$ 27,125	$ (27,125)
Ending balance at Dec. 31, 2022		$ 27,125								$ 0	$ 27,125
Ending balance (in shares) at Dec. 31, 2022		27,125,000								0	27,125,000
Beginning balance (in shares) at Dec. 31, 2021	[1]		867,499		0
Beginning balance at Dec. 31, 2021		$ (226)	$ 0		$ 0		$ 0	$ 0	$ (226)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of common units to common stock (in shares)	[1]		(867,499)		867,499
Stock-based compensation expense, including acceleration and settlement of former Talaris Therapeutics, Inc. stock-based awards in connection with reverse merger		$ 195					195
Issuance of common stock from exercise of stock options, including early exercises (in shares)		0
Unrealized gain on short-term investments		$ 0
Net loss		(19,701)							(19,701)
Ending balance at Dec. 31, 2022		$ (19,732)	$ 0		$ 0		195	0	(19,927)
Ending balance (in shares) at Dec. 31, 2022		867,499	0	[1]	867,499	[1]
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series A convertible preferred units, net of issuance costs (in shares)											92,200,000
Issuance of Series A convertible preferred units, net of issuance costs											$ 91,823
Issuance of Series A convertible preferred stock pursuant to anti-dilution provision of license agreement with Pfizer Inc. (in shares)											8,823,529
Issuance of Series A convertible preferred stock pursuant to anti-dilution provision of license agreement with Pfizer Inc.											$ 8,824
Conversion of convertible preferred stock to common stock in connection with reverse merger (in shares)											(128,148,529)
Conversion of convertible preferred stock to common stock in connection with reverse merger											$ (127,772)
Ending balance at Dec. 31, 2023		$ 0								$ 0	$ 0
Ending balance (in shares) at Dec. 31, 2023		0								0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of convertible preferred stock to common stock in connection with reverse merger (in shares)		10,222,414			10,222,414	[1]
Conversion of convertible preferred stock to common stock in connection with reverse merger		$ 127,772			$ 1		127,771
Issuance of common stock in the pre-closing financing, net of issuance costs (in shares)	[1]				4,092,035
Issuance of common stock in the pre-closing financing, net of issuance costs		70,468					70,468
Stock Issued During Period, Value, Reverse Recapitalization					$ 1
Issuance of common stock to former stockholders of Talaris Therapeutics, Inc. in connection with reverse merger (in shares)	[1]				4,459,651
Issuance of common stock to former stockholders of Talaris Therapeutics, Inc. in connection with reverse merger		68,892					68,891
Reverse Merger transaction costs		(6,112)					(6,112)
Stock-based compensation expense, including acceleration and settlement of former Talaris Therapeutics, Inc. stock-based awards in connection with reverse merger		$ 5,769					5,769
Issuance of common stock from exercise of stock options, including early exercises (in shares)		695,142			695,142	[1]
Issuance of common stock from exercise of stock options, including early exercises		$ 7					7
Vesting of early exercised stock options		35					35
Issuance of common stock upon vesting of restricted stock units (in shares)	[1]				830
Unrealized gain on short-term investments		67						67
Net loss		(42,124)							(42,124)
Ending balance at Dec. 31, 2023		$ 205,042	$ 0		$ 2		$ 267,024	$ 67	$ (62,051)
Ending balance (in shares) at Dec. 31, 2023		20,337,571	0	[1]	20,337,571	[1]
[1] * Amounts have been restated for the impact of the reverse merger outlined further within Notes 1 and 3 and the May 3, 2022 stock split outlined further within Note 10.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating activities:
Net loss	$ (42,124)	$ (19,701)
Adjustments to reconcile net loss to net cash used in operating activities:
In-process research and development expense	8,824	12,125
Stock-based compensation	5,769	195
Non-cash lease expense	126	15
Depreciation on property and equipment	33	6
Accretion of discount on short-term investments	(522)	0
Realized gain on short-term investments	(17)	0
Other non-cash items	(2)	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,615)	(54)
Other non-current assets	(747)	0
Accounts payable	(44)	193
Accrued expenses and other current liabilities	2,325	763
Operating lease liabilities	(87)	0
Net cash used in operating activities	(28,081)	(6,458)
Investing activities:
Purchases of property and equipment	(56)	(68)
Acquisition of in-process research and development	0	(5,000)
Purchases of investments	(16,604)	0
Maturities of investments	20,500	0
Net cash provided by (used in) investing activities	3,840	(5,068)
Financing activities:
Proceeds from issuance of Series A convertible preferred stock, net of issuance costs	91,823	20,000
Proceeds from exercises of stock options	144	0
Payment of reverse merger costs	(6,107)	0
Proceeds from pre-merger financing, net of issuance costs	70,468	0
Cash acquired in connection with reverse merger	392	0
Proceeds from issuance of related party note payable	0	250
Repayment of related party note payable	0	(400)
Net cash provided by financing activities	156,720	19,850
Net increase in cash, cash equivalents and restricted cash	132,479	8,324
Cash, cash equivalents and restricted cash—Beginning of period	8,474	150
Cash, cash equivalents and restricted cash—End of period	140,953	8,474
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	140,726	8,258
Restricted cash	227	216
Total cash, cash equivalents and restricted cash	140,953	8,474
Non-cash investing and financing activities:
Right-of use asset obtained in exchange for new operating lease liability	0	491
Issuance of Series A convertible preferred stock in exchange for acquired in-process research and development	8,824	7,125
Purchases of property and equipment included in accounts payable and accrued expenses	0	19
Unpaid reverse merger costs included in accounts payable	$ 5	$ 0

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Nature of Business Overview Tourmaline Bio, Inc. (the “Company”) is a late-stage clinical biotechnology company focused on developing transformative medicines that dramatically improve the lives of patients with life-altering immune and inflammatory diseases. The Company is developing TOUR006, a fully human monoclonal antibody that selectively binds to interleukin-6, a key proinflammatory cytokine involved in the pathogenesis of many autoimmune and inflammatory disorders. The Company’s corporate headquarters are in New York, New York. The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive clinical testing and regulatory approval, prior to commercialization. These efforts will require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from product sales. Reverse Merger and Pre-Merger Financing Transaction On October 19, 2023, the Company completed its reverse merger with Tourmaline Sub, Inc. (formerly Tourmaline Bio, Inc.) (“Legacy Tourmaline”) in accordance with the terms of the Agreement and Plan of Merger, dated as of June 22, 2023 (the “Merger Agreement”), by and among the Company, Terrain Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of the Company (“Merger Sub”), and Legacy Tourmaline, pursuant to which, among other matters, Merger Sub merged with and into Legacy Tourmaline, with Legacy Tourmaline surviving as a wholly owned subsidiary of the Company (the “Reverse Merger”). In connection with the completion of the Reverse Merger, the Company changed its name from “Talaris Therapeutics, Inc.” to “Tourmaline Bio, Inc.,” and the business conducted by the Company became primarily the business conducted by Legacy Tourmaline. References to “the Company” refer to Legacy Tourmaline for periods prior to the closing of the Reverse Merger, and to Tourmaline Bio, Inc. (formerly Talaris Therapeutics, Inc., or “Talaris”) for all other periods, as the context requires. Immediately prior to the effective time of the Reverse Merger, Talaris effected a 1-for-10 reverse stock split of its common stock (the “Reverse Stock Split”). At the effective time of the Reverse Merger, the Company issued an aggregate of 15,877,090 shares of Company common stock to the Legacy Tourmaline stockholders, based on the exchange ratio of approximately 0.07977 shares of Company common stock for each share of Legacy Tourmaline common stock, including those shares of Legacy Tourmaline common stock issued upon the conversion of Legacy Tourmaline Series A convertible preferred stock and those shares of the Legacy Tourmaline common stock issued in the Pre-Merger Financing Transaction (as defined below), resulting in 20,336,741 shares of Company common stock being issued and outstanding following the effective time of the Reverse Merger. At the effective time of the Reverse Merger, Legacy Tourmaline’s 2022 Equity Incentive Plan was assumed by the Company, and each outstanding and unexercised option to purchase shares of Legacy Tourmaline common stock immediately prior to the effective time of the Reverse Merger was assumed by the Company and converted into an option to purchase shares of Company common stock, with necessary adjustments to the number of shares and exercise price to reflect the exchange ratio. The Reverse Merger was accounted for as a reverse recapitalization in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”). Under this method of accounting, Legacy Tourmaline was deemed to be the accounting acquirer for financial reporting purposes. This determination was primarily based on the expectation that, immediately following the Reverse Merger: (i) Legacy Tourmaline’s stockholders own a substantial majority of the voting rights in the combined company; (ii) Legacy Tourmaline’s largest stockholders retain the largest interest in the combined company; (iii) Legacy Tourmaline designated a majority (five of seven) of the initial members of the board of directors of the combined company; and (iv) Legacy Tourmaline’s executive management team became the management team of the combined company. Accordingly, for accounting purposes: (i) the Reverse Merger was treated as the equivalent of Legacy Tourmaline issuing stock to acquire the net assets of Talaris; (ii) the net assets of Talaris are recorded at their acquisition-date fair value in the consolidated financial statements of Legacy Tourmaline and (iii) the reported historical operating results of the combined company prior to the Reverse Merger are those of Legacy Tourmaline. Historical common share figures of Legacy Tourmaline have been retroactively restated based on the exchange ratio of 0.07977. Additional information regarding the accounting for the Reverse Merger is included in Note 3, “Reverse Merger”. Concurrently with the execution and delivery of the Merger Agreement, and in order to provide Legacy Tourmaline with additional capital for its development programs, Legacy Tourmaline entered into a Securities Purchase Agreement (the “Private Placement Agreement”), with certain investors named therein (the “Private Placement Investors”), pursuant to which, subject to the terms and conditions of the Private Placement Agreement, immediately prior to the effective time of the Reverse Merger, Legacy Tourmaline issued and sold, and the Private Placement Investors purchased 4,092,035 shares (as effected by the exchange ratio described above) of Legacy Tourmaline common stock for gross proceeds of approximately $75.0 million (the “Pre-Merger Financing Transaction”). Liquidity As of December 31, 2023, the Company had cash, cash equivalents, and investments of $203.0 million. As outlined further within Note 17, “Subsequent Events”, the Company completed a public offering of its common stock in January 2024 (the “January 2024 Offering”), resulting in net proceeds of $161.3 million after deducting underwriting discounts and commissions and offering expenses. The Company expects that its existing cash, cash equivalents and investments, including the net proceeds received from the January 2024 Offering, will enable it to fund its expected operating expenses and capital expenditure requirements for at least 12 months from March 19, 2024, the filing date of this Annual Report on Form 10-K. The Company expects to finance its future cash needs through a combination of equity or debt financings, collaborations, licensing arrangements and strategic alliances.

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and US GAAP, as found in the Accounting Standards Codification (“ASC”) of the Financial Accounting Standards Board (“FASB”). The consolidated financial statements include the accounts of Tourmaline Bio, Inc. and its wholly owned subsidiary, Tourmaline Sub, Inc. All intercompany transactions and balances have been eliminated in consolidation. Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision-maker in deciding how to allocate resources and assess performance. The Company’s chief operating decision maker, the Company’s chief executive officer, views the Company’s operations and manages its business as a single operating segment. The Company operates only in the United States. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, accrued expenses and stock-based compensation expense. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. Actual results could differ from those estimates. Fair Value of Financial Instruments ASC Topic 820, Fair Value Measurement , (“ASC 820”) establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. • Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Cash Equivalents Cash equivalents are highly-liquid investments that are readily convertible into cash with original maturities of three months or less when purchased. These assets include investments in money market funds that invest in U.S. Treasury and government agency obligations. Cash equivalents are reflected at fair value based on quoted market prices, as further described in Note 5, “Fair Value Measurements”. Investments Investments consist of securities with original maturities greater than three months when purchased. Short-term investments consist of investments that are available for use in current operations. Long-term investments consist of investments with maturities of greater than one year that are not available for use in current operations. The Company did not maintain any long-term investments as of December 31, 2023 or 2022. The Company classifies all of its investments as available-for-sale securities. Accordingly, these investments are recorded at fair value. Realized gains and losses and amortization and accretion of discounts and premiums are included in “Other income, net”. Unrealized gains and losses on available-for-sale securities are included in “Accumulated other comprehensive income” as a component of stockholders’ equity (deficit) until realized. For available-for-sale debt securities in unrealized loss positions, the Company is required to assess whether to record an allowance for credit losses using an expected loss model. A credit loss is limited to the amount by which the amortized cost of an investment exceeds its fair value. A previously-recognized credit loss may be decreased in subsequent periods if the Company’s estimate of fair value for the investment increases. To determine whether to record a credit loss, the Company considers, among other factors, adverse conditions related to the security, industry, or geographic area, failure of the issuer to make scheduled payments, and changes in the issuer’s credit rating. Property and Equipment Property and equipment are recorded at cost and consist of computer and office equipment and leasehold improvements. The Company capitalizes property and equipment that is acquired for research and development activities and that has alternative future use. Expenditures for repairs and maintenance are recorded to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. Leasehold improvements are depreciated over the lesser of their useful lives or the term of the lease. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method. Impairment of Long-Lived Assets The Company reviews long-lived assets when events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. Recoverability is measured by comparing the carrying value of the asset to the future undiscounted cash flows from the use and eventual disposition of the asset. If an asset is considered to be impaired, the impairment loss to be recognized is measured as the amount by which the carrying value of the asset exceeds its fair value. Leases The Company accounts for leases pursuant to ASC Topic 842, Leases (“ASC 842”). Upon the adoption ASC 842, the Company elected to utilize certain practical expedients, which among other things, permit the Company to not separate lease and non-lease components. Additionally, the Company elected an accounting policy whereby it does not apply the recognition requirements of ASC 842 to short-term leases with a term of 12 months or less. The Company determines if an arrangement is or contains a lease by evaluating whether the arrangement conveys the right to use an identified asset and whether the Company obtains substantially all of the economic benefits from and has the ability to direct the use of the asset. If a lease is determined to exist, at the lease commencement date, the Company recognizes a lease liability and a right-of-use (“ROU”) asset representing its right to use the underlying asset over the lease term. The Company determines the lease term at the lease commencement date, with the lease term including periods covered by renewal options that are reasonably certain of being exercised and periods covered by termination options that are reasonably certain of not being exercised. The initial measurement of the lease liability is calculated on the basis of the present value of the remaining lease payments and the ROU asset is measured on the basis of this liability, adjusted by prepaid and accrued rent, lease incentives, and initial direct costs. The subsequent measurement of a lease is dependent on whether the lease is classified as an operating lease or a finance lease. Operating lease cost is recognized on a straight-line basis over the lease term, with the cost presented as a component of general and administrative expenses in the consolidated statements of operations and comprehensive loss. The Company has not recognized any financing leases to date. The Company’s lease requires other payments such as costs related to service components, real estate taxes, common area maintenance, and insurance. These costs are generally variable in nature and based on the actual costs incurred and required by the lease. As the Company has elected to not separate lease and non-lease components for all classes of underlying assets, all variable costs associated with the lease are expensed in the period incurred and presented and disclosed as variable lease costs. ASC 842 requires that a lessee use the rate implicit in the lease when measuring the lease liability and ROU asset, unless that rate is not readily determinable. When the rate implicit in the lease is not readily determinable, the Company uses its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of future lease payments. The Company gives consideration to the Company’s credit standing, the term of the lease, total lease payments and adjusts for the impacts of collateral, as necessary, when calculating its incremental borrowing rates. Research and Development Expenses Expenditures relating to research and development are expensed as incurred. Research and development expenses include external expenses incurred under arrangements with third parties; consulting costs; salaries and personnel-related costs, including non-cash stock-based compensation expense; license fees to acquire in-process research and development that does not have an alternative future use and other expenses. Non-refundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. Where contingent milestone payments are due to third parties under research and development or license agreements, the milestone payment obligations are expensed when the related milestone events are achieved. As part of the process of preparing the consolidated financial statements, the Company is required to estimate its accrued research and development expenses as of each balance sheet date. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. This process involves reviewing open contracts, communicating with internal personnel to identify services that have been performed on the Company’s behalf and estimating the level of service performed and the associated cost incurred for the service when the Company has not yet been invoiced or otherwise notified of the actual cost. The Company periodically confirms the accuracy of its estimates with its service providers and makes adjustments if necessary. The majority of the Company’s service providers invoice monthly in arrears for services performed or when contractual milestones are met. The financial terms of agreements with these service providers are subject to negotiation, vary from contract-to-contract and may result in uneven payment flows. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense. Intellectual Property Expenses The Company expenses legal costs related to patent applications as they are incurred. Such costs are classified as general and administrative expenses within the consolidated statements of operations and comprehensive loss. Stock-Based Compensation The Company accounts for stock-based payments in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). This guidance requires all stock-based payments, including grants of stock options and restricted common units, to be recognized as expense in the consolidated statements of operations and comprehensive loss based on their grant date fair values. For stock options granted to employees, non-employees and members of the Company’s Board of Directors for their services on the Board of Directors, the Company estimates the grant date fair value of each stock option using the Black-Scholes option-pricing model. For stock-based payments subject to service-based vesting conditions, the Company recognizes stock-based compensation expense equal to the grant date fair value of stock-based payment on a straight-line basis over the requisite service period. Prior to the Company being publicly-traded, Legacy Tourmaline estimated the grant date fair value of its common stock using an appropriate valuation methodology, in accordance with the framework of the American Institute of Certified Public Accountants’ Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation . Each valuation methodology included estimates and assumptions that required the Company’s judgment. These estimates and assumptions included a number of objective and subjective factors, including external market conditions, guideline public company information, the prices at which the Company sold convertible preferred stock to third parties in arms’ length transactions, the rights and preferences of securities senior to the Company’s common stock at the time and the likelihood of achieving a liquidity event such as an initial public offering or sale. Significant changes to the assumptions used in the valuations could result in different fair values at each valuation date. In addition to the grant date fair value of the Company’s common stock, the Black‑Scholes option pricing model requires the input of certain subjective assumptions, including (i) the calculation of expected term of the stock-based payment, (ii) the risk‑free interest rate, (iii) the expected stock price volatility and (iv) the expected dividend yield. The Company uses the simplified method as prescribed by SEC Staff Accounting Bulletin No. 107 to calculate the expected term for stock options granted to employees as the Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The Company determines the risk‑free interest rate based on a treasury instrument whose term is consistent with the expected term of the stock options. Because the Company has only been publicly-traded for a short period of time, there is a lack of Company‑specific historical and implied volatility data. Accordingly, the Company bases its estimates of expected volatility on the historical volatility of a group of publicly-traded companies with similar characteristics to itself, including stage of product development and therapeutic focus within the life sciences industry. Historical volatility is calculated over a period of time commensurate with the expected term of the stock-based payment. The Company uses an assumed dividend yield of zero as the Company has never paid dividends on its common stock, nor does it expect to pay dividends on its common stock in the foreseeable future. The Company accounts for forfeitures of all stock-based payments when such forfeitures occur . Income Taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes , which provides for deferred taxes using an asset and liability approach. 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 financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. A valuation allowance against deferred tax assets is recorded if, based on the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions using a more-likely-than-not threshold for recognizing and resolving uncertain tax positions. The evaluation of uncertain tax positions is based on factors, including, but not limited to, changes in the law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, new audit activity and changes in facts or circumstances related to a tax position. Interest and penalty charges, if any, related to income taxes would be classified as a component of the “Provision for income taxes” in the consolidated statements of operations and comprehensive loss. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders is presented in conformity with the two-class method required for participating securities. The Company considers its Series A convertible preferred stock and common stock issued subject to repurchase (related to early exercised stock options) to be participating securities. Net loss is attributed to common stockholders and participating securities based on their participation rights. Net loss attributable to common stockholders is not allocated to the Series A convertible preferred stock or common stock issued subject to repurchase as these holders do not have a contractual obligation to share in any losses. Under the two-class method, basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share attributable to common stockholders includes the effect, if any, from common stock issued subject to repurchase and the potential exercise or conversion of securities such as stock options and convertible preferred stock, which would result in the issuance of incremental shares of common stock. The Company has not adjusted its weighted average number of common shares outstanding in the calculation of diluted loss per share attributable to common stockholders as the Company reported a net loss for all periods presented and the effect of the aforementioned securities is anti-dilutive. Concentration of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk primarily consist of cash, cash equivalents and investments. Cash balances are deposited with federally-insured financial institutions in the United States and may, at times, exceed federally-insured limits. The Company maintains its cash, cash equivalents and investments with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. The Company’s cash equivalents are comprised of money market funds that are invested in U.S. Treasury and government agency obligations. The Company’s investments are comprised of commercial paper, government securities, and corporate debt securities. Credit risk in these securities is reduced as a result of the Company’s investment policy to limit the amount invested in any single issuer and to only invest in securities of a high credit quality. The Company has no significant off-balance sheet risk such as foreign exchange contracts, option contracts or other foreign hedging arrangements. Recently Adopted Accounting Pronouncements In June 2016, the FASB issued Accounting Standards Update (“ASU”) 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . This standard requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and it establishes additional disclosure requirements related to credit risks. For available-for-sale debt securities with expected credit losses, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. This guidance was originally effective for annual reporting periods beginning after December 15, 2020 and interim periods within fiscal years beginning after December 31, 2021, and early adoption was permitted. In November 2019, the FASB subsequently issued ASU 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates , whereby the effective date of this standard was deferred to annual reporting periods beginning after December 15, 2022, including interim periods within those annual reporting periods, and early adoption is still permitted. Accordingly, the Company adopted this new standard effective January 1, 2023, and the adoption of ASU 2016-13 did not have an impact on the consolidated financial statements. Recent Accounting Pronouncements - Yet to be Adopted In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures . This guidance is intended to improve reportable segment disclosure requirements through enhanced disclosures as well as clarify that entities with a single reportable segment are subject to new and existing segment reporting requirements. This guidance is effective for annual periods in fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. Entities must apply this guidance on a retrospective basis. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statements. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures

Reverse Merger

Reverse Merger	12 Months Ended
	Dec. 31, 2023
Reverse Recapitalization [Abstract]
Reverse Merger	Reverse Merger As described in Note 1, “Nature of Business”, Merger Sub merged with and into Legacy Tourmaline, with Legacy Tourmaline surviving as a wholly owned subsidiary of the Company on October 19, 2023. The Reverse Merger was accounted for as a reverse recapitalization in accordance with U.S. GAAP with Legacy Tourmaline as the accounting acquirer of Talaris. Under reverse recapitalization accounting, the assets and liabilities of Talaris were recorded at their fair value in Tourmaline’s financial statements at the effective time of the Merger. No goodwill or intangible assets were recognized. Consequently, the consolidated financial statements of the Company reflect the operations of Legacy Tourmaline for accounting purposes together with a deemed issuance of shares, equivalent to the shares held by the former stockholders of Talaris, the legal acquirer, and a recapitalization of the equity of Legacy Tourmaline, the accounting acquirer. The Company acquired the following assets and liabilities as part of the Reverse Merger (in thousands): Amount Cash and cash equivalents $ 392 Short-term investments 65,515 Prepaid expenses and other current assets 4,254 Accounts payable (726) Accrued expenses (543) Net assets acquired $ 68,892 The Company incurred $2.9 million in stock-based compensation expense as a result of the acceleration of vesting and settlement of Talaris share-based awards at the time of the Reverse Merger. In the consolidated statement of operations and comprehensive loss for the year ended December 31, 2023, $1.4 million and $1.5 million were recorded as research and development expense and general and administrative expense, respectively. Additionally, the Company incurred transaction costs of $6.1 million, which were recorded as a reduction to additional paid-in capital in the consolidated statement of convertible preferred stock and stockholders’ equity for the year ended December 31, 2023.

Pfizer License Agreement

Pfizer License Agreement	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Pfizer License Agreement	Pfizer License Agreement On May 3, 2022 (the “Effective Date”), the Company entered into a License Agreement (the “Pfizer License Agreement”) with Pfizer Inc. (“Pfizer”), pursuant to which the Company obtained an exclusive, sublicensable, royalty-bearing, worldwide right to use and license under certain know-how for the development, commercialization and manufacture of PF-04236921 (the “Compound”, now known as TOUR006) and any pharmaceutical or biopharmaceutical product incorporating the Compound (the “Product”), for the treatment, diagnosis, or prevention of any and all diseases, disorders, illnesses and conditions in humans and animals. In consideration for the license and other rights the Company received under the Pfizer License Agreement, the Company paid Pfizer an upfront payment of $5.0 million and issued to Pfizer 7,125,000 Series A preferred units of Tourmaline Bio, LLC (the predecessor of Legacy Tourmaline), which subsequently converted to 7,125,000 shares of Series A convertible preferred stock of Legacy Tourmaline, representing a 15% interest in the Company on a fully-diluted basis at the time of issuance. The units were issued for $1.00 per unit, representing a total value of $7.1 million. In accordance with ASC Topic 805, Business Combinations , the Pfizer License Agreement was accounted for as an asset acquisition as the licensed compound represented substantially all of the fair value of the gross assets acquired. On the Effective Date, the licensed compound had not yet received regulatory approval and did not have an alternative use. Accordingly, the total consideration transferred of $12.1 million was recorded as research and development expense in the consolidated statement of operations and comprehensive loss for the year ended December 31, 2022. As additional consideration for the license, the Company is obligated to pay Pfizer up to $128.0 million upon the achievement of specific development and regulatory milestones. The Company is also obligated to pay Pfizer up to $525.0 million upon the first achievement of specific sales milestones. The Company is also obligated to pay Pfizer a marginal royalty rate in the low double digits (less than 15%), subject to specified royalty reductions. The royalty term, on a Product-by-Product and country-by-country basis, begins on the first commercial sale of such Product and expires upon the later of twelve years following the date of the first commercial sale or the expiration of regulatory exclusivity protecting such Product. In the event the Company completes a Significant Transaction (as defined in the Pfizer License Agreement), the Company will be obligated to pay Pfizer a one-time payment in the low-eight digits (up to $20.0 million); the amount of such payment is based on the timing of the transaction. As of December 31, 2023, the Company does not owe any milestone or royalties under the Pfizer License Agreement and no such milestones or royalties have been paid to date. The Pfizer License Agreement originally contained an anti-dilution provision allowing Pfizer to maintain a 15% interest in the Company on a fully-diluted basis unless and until certain thresholds are met, whereupon the anti-dilution provision would no longer apply. As outlined further within Note 9, “Convertible Preferred Stock”, on May 2, 2023, the Company issued 8,823,529 additional shares of Series A convertible preferred stock to Pfizer pursuant this anti-dilution provision. The Company recognized research and development expense of $8.8 million related to this issuance of Series A convertible preferred stock. Subsequent to the issuance of these additional shares of Series A convertible preferred stock, the anti-dilution provision is no longer in force and effect.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company measures the fair value of money market funds based on quoted prices in active markets for identical securities. Investments also include commercial paper and government securities which are valued either based on recent trades of securities in inactive markets or based on quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data. The carrying amounts reflected in the consolidated balance sheets for cash, prepaid expenses and other current assets, accounts payable and accrued expenses and other current liabilities approximate their fair values, due to their short-term nature. Assets measured at fair value on a recurring basis as of December 31, 2023 were as follows (in thousands): Total Level 1 Level 2 Level 3 Money market funds, included in cash and cash equivalents $ 4,604 $ 4,604 $ — $ — Short-term investments: Commercial paper 32,555 — 32,555 — Government securities 26,724 7,907 18,817 — Corporate debt securities 2,947 — 2,947 — Total $ 66,830 $ 12,511 $ 54,319 $ —

Investments

Investments	12 Months Ended
	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Cash equivalents and short-term investments as of December 31, 2023 were comprised as follows (in thousands): Amortized Cost Unrealized Gains Unrealized Losses Fair Value Money market funds, included in cash and cash equivalents $ 4,604 $ — $ — $ 4,604 Short-term investments: Commercial paper 32,515 44 (4) 32,555 Government securities 26,703 25 (4) 26,724 Corporate debt securities 2,941 6 — 2,947 Total $ 66,763 $ 75 $ (8) $ 66,830 The Company maintained no cash equivalents or investments as of December 31, 2022. As of December 31, 2023, the aggregate fair value of securities that were in an unrealized loss position for less than twelve months was $49.3 million. The Company held no securities that were in an unrealized loss position for more than twelve months as of December 31, 2023. Based upon its assessment of securities in an unrealized loss position, the Company did not record any allowances for credit losses during the year ended December 31, 2023.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net as of December 31, 2023 and 2022 was comprised as follows (in thousands): Estimated Useful Life December 31, 2023 2022 Leasehold improvements Shorter of useful life or remaining lease term $ 74 $ 64 Computer and office equipment 3 years 49 23 Total property and equipment, gross 123 87 Less: accumulated depreciation (38) (6) Total property and equipment, net $ 85 $ 81 Depreciation expense was less than $0.1 million for each of the years ended December 31, 2023 and 2022.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2023
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities as of December 31, 2023 and 2022 were comprised as follows (in thousands): December 31, 2023 2022 Accrued bonus $ 1,994 $ 446 Accrued clinical and manufacturing costs 438 185 Accrued consulting fees 692 81 Accrued legal fees 237 54 Other accrued expenses and other current liabilities 349 34 Total accrued expenses and other current liabilities $ 3,710 $ 800

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2023
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	Convertible Preferred Stock On April 18, 2022, the Company entered into a Securities Purchase Agreement (the “Initial Series A Securities Purchase Agreement”) with various entities and individuals for the purchase of Series A convertible preferred units. As part of the Initial Series A Securities Purchase Agreement, the Company authorized the issuance and sale of up to 20,000,000 shares of its Series A convertible preferred units at a price of $1.00 per unit for total proceeds of $20.0 million. The Series A convertible preferred units were convertible into the Company’s Common Units at a 1:1 ratio. The obligations of the parties to purchase and sell the Series A convertible preferred units were subject to the Company entering into the Pfizer License Agreement. As outlined further within Note 4, “Pfizer License Agreement”, the Company also issued to Pfizer 7,125,000 Series A convertible preferred units in May 2022 conjunction with the Pfizer License Agreement. On September 2, 2022, Legacy Tourmaline converted from Tourmaline Bio, LLC, a Delaware limited liability company, to Tourmaline Bio, Inc., a Delaware corporation (the “Conversion”). As part of the Conversion, Series A convertible preferred units were converted at a 1:1 ratio to shares of Series A convertible preferred stock. Upon the Conversion, the Company was authorized to issue up to 27,125,000 shares of Series A convertible preferred stock with a par value of $0.0001. The Company subsequently entered into a Series A Preferred Stock Purchase Agreement on May 2, 2023 (the “Closing Date”) with various entities and individuals for the purchase of additional shares of Series A convertible preferred stock (the “Series A Extension”). On the Closing Date, the Company authorized the issuance and sale of 92,200,000 shares of Series A convertible preferred stock at a price of $1.00 per share for total gross proceeds of $92.2 million. In addition, pursuant to the anti-dilution provision of the Pfizer License Agreement, the Company issued 8,823,529 additional shares of Series A convertible preferred stock to Pfizer in connection with the Series A Extension and recognized corresponding research and development expense of $8.8 million during the second quarter of 2023. The additional shares of Series A convertible preferred stock had the same terms, conditions, rights and preferences as the Series A convertible preferred stock issued during the year ended December 31, 2022. Upon consummation of the Series A Extension, the anti-dilution provision of the Pfizer License Agreement was no longer in force and effect. Prior to the completion of the Reverse Merger, the Company classified its Series A convertible preferred stock outside of permanent equity as the shares had redemption features that were not entirely within the control of the Company. Upon the consummation of the Reverse Merger, all outstanding shares of Series A convertible preferred stock were converted into 10,222,414 shares of common stock. No shares of preferred stock were outstanding as of December 31, 2023.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2023
Equity [Abstract]
Common Stock	Common Stock On May 3, 2022, the Company effected a stock split, and each common unit in Tourmaline Bio, LLC was exchanged for 6.39697802 common units. Subsequently, as part of the September 2, 2022 Conversion outlined within Note 9 “Convertible Preferred Stock”, the Company converted all its equity interests of Tourmaline Bio, LLC into equity interests of Tourmaline Bio, Inc. Each common unit in the LLC was exchanged for 1.00 shares of the Company’s common stock. As of December 31, 2023, the Company was authorized to issue 140,000,000 shares of voting common stock and 10,000,000 shares of non-voting common stock. Holders of voting common stock are entitled to one vote per share. In addition, holders of voting common stock are entitled to receive dividends, if and when declared by the Company’s Board of Directors. As of December 31, 2023, no dividends had been declared. As of December 31, 2023 and 2022, the Company had reserved for future issuance the following number of shares of common stock: December 31, 2023 2022 Conversion of outstanding Series A convertible preferred stock — 2,163,764 Exercises of outstanding stock options under 2022 Equity Incentive Plan 1,403,409 404,673 Exercises of outstanding stock options under 2023 Equity Incentive Plan 1,042,291 — Vesting of restricted stock units under 2023 Equity Incentive Plan 19,113 — Common stock subject to repurchase related to early exercised stock options 388,943 — Future issuances under 2022 Equity Incentive Plan — 353,142 Future issuances under 2023 Equity Incentive Plan 971,444 — Future issuances under 2023 Employee Stock Purchase Plan 203,367 — Total shares reserved for future issuance 4,028,567 2,921,579

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation 2022 Equity Incentive Plan On September 2, 2022, the Board of Directors and the stockholders of the Company adopted the 2022 Equity Incentive Plan (the “2022 Plan”), which provided for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards and other stock awards to employees, consultants, and non-employee directors of the Company. 2023 Equity Incentive Plan On October 17, 2023, the Company adopted the 2023 Equity Incentive Plan (the “2023 Plan”) which became effective upon completion of the Reverse Merger. The 2023 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards and other forms of awards to employees, consultants, and non-employee directors of the Company. The terms of stock award agreements, including vesting requirements, are determined by the Company’s Board of Directors and are subject to the provisions of the 2023 Plan. The term of each stock option shall be no more than ten years from the date of grant. Following the effectiveness of the 2023 Plan, no further grants will be made under the 2022 Plan; however, any outstanding equity awards granted under the 2022 Plan will continue to be governed by the terms of the 2022 Plan. The 2023 Plan initially provided for the issuance of up to 2,033,677 shares of common stock (the “Initial EIP Share Reserve”). Subject to any other adjustments as defined in the 2023 Plan, such aggregate number of shares of common stock will automatically increase on January 1st of each year for a period of ten years commencing on January 1, 2024 and ending on (and including) January 1, 2033, in an amount equal to 5% of the total number of shares of common stock issued and outstanding determined as of the day prior to such increase; provided, however that the board of directors may act prior to January 1st of a given year to provide that the increase for such year will be a lesser number of shares of common stock. The aggregate maximum number of shares of common stock that may be issued pursuant to the exercise of incentive stock options is three multiplied by the Initial EIP Share Reserve. As of December 31, 2023, there were 971,444 shares available for issuance under the 2023 Plan. 2023 Employee Stock Purchase Plan On October 17, 2023, the Company adopted the 2023 Employee Stock Purchase Plan (the “2023 ESPP”), which became effective upon completion of the Reverse Merger. The maximum number of shares of common stock that may be issued under the 2023 ESPP will not exceed 203,367 shares (the “Initial ESPP Share Reserve”), plus the number of shares of common stock that are automatically added on January 1st of each year for a period of up to ten years commencing on January 1, 2024 and ending on (and including) January 1, 2033, in an amount equal to the lesser of (x) 1% of the total number of shares of common stock issued and outstanding determined as of the day prior to such increase and (y) a number of shares equal to three times the Initial ESPP Share Reserve. Notwithstanding the foregoing, the board of directors may act prior to the first day of any calendar year to provide that there will be no January 1st increase in the share reserve for such calendar year or that the increase in the share reserve for such calendar year will be a lesser number of shares of common stock than would otherwise occur pursuant to the preceding sentence. No offering periods under the 2023 ESPP had been initiated as of December 31, 2023. Total stock-based compensation expense recognized in the consolidated statements of operations and comprehensive loss for the years ended December 31, 2023 and 2022 was as follows (in thousands): Year Ended December 31, 2023 2022 Research and development $ 2,322 $ 165 General and administrative 3,447 30 Total stock-based compensation expense $ 5,769 $ 195 Stock Option Activity The estimated grant-date fair value of the Company’s stock options was calculated using the Black-Scholes option pricing model, based on the following assumptions: Year Ended December 31, 2023 2022 Risk-free interest rate 3.4% – 4.8% 3.7% – 4.4% Dividend yield —% —% Volatility 82.2% – 86.1% 83.1% – 86.3% Expected term (in years) 5.5 – 6.1 3.3 – 6.1 The weighted-average fair value of the Company’s common stock utilized in the valuation of stock options granted during the years ended December 31, 2023 and 2022 was $8.33 and $4.39 per share, respectively. Using the Black-Scholes option pricing model, the weighted-average grant date fair value of stock options granted during the year ended December 31, 2023 and 2022 was $6.60 and $4.26 per share, respectively. The following table summarizes changes in stock option activity during the year ended December 31, 2023: Options Weighted- Weighted- Aggregate Intrinsic Value Outstanding as of December 31, 2022 404,673 $ 0.14 7.2 $ 1,722 Granted 2,736,169 $ 8.33 Exercised (695,142) $ 0.21 Cancelled — $ — Outstanding as of December 31, 2023 2,445,700 $ 9.29 9.6 $ 41,320 Exercisable as of December 31, 2023 23,896 $ 11.02 9.7 $ 362 The aggregate intrinsic value of stock options exercised during the year ended December 31, 2023 was $1.8 million. No stock options were exercised during the year ended December 31, 2022. As of December 31, 2023, the total unrecognized stock-based compensation expense related to unvested stock options was $16.8 million, which the Company expects to recognize over a weighted-average period of approximately 3.5 years. Early Exercise of Stock Options The 2022 Plan and certain stock options issued under the 2022 Plan were amended in February 2023 to permit the stock option holder to early exercise at any time between the grant date and the vesting date. The amendment did not result in any incremental stock-based compensation expense. For the year ended December 31, 2023, certain employees, advisors and non-employee directors early exercised 647,386 stock options. In the event of termination of an employee, advisor or non-employee director, the Company can repurchase early exercised and unvested stock options for a period of six months following the later of (i) the termination date of the employee or non-employee director or (ii) the exercise date. The Company received $0.1 million in cash proceeds related to the early exercise of stock options during the year ended December 31, 2023. As a result of the aforementioned repurchase right, the Company initially records the proceeds received from the early exercise of stock options as a liability in the consolidated balance sheets. Amounts are reclassified to additional paid-in capital when the underlying stock options vest and the Company’s right of repurchase lapses. The aggregate liability associated with the early exercise of stock options was $0.1 million as of December 31, 2023. As of December 31, 2023, 388,943 early exercised stock options remain unvested. No stock options were early exercised during the year ended December 31, 2022, and consequently there were no unvested early exercised stock options as of that date. The shares of common stock subject to repurchase related to early exercised stock options are legally outstanding, as each holder is deemed to be a common stockholder that has dividend and voting rights during the vesting term. Restricted Stock Unit Activity The following table summarizes changes in restricted stock unit activity during the year ended December 31, 2023: Shares Weighted- Unvested as of December 31, 2022 — $ — Granted 19,943 11.89 Vested (830) 11.89 Cancelled — — Unvested as of December 31, 2023 19,113 $ 11.89 The total grant date fair value of restricted stock units vested for the year ended December 31, 2023 was less than $0.1 million. As of December 31, 2023, the total unrecognized stock-based compensation expense related to unvested restricted stock units was $0.2 million, which the Company expects to recognize over a weighted-average period of approximately 3.7 years.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company recorded no income tax benefit for the net loss incurred for the years ended December 31, 2023 and 2022 due to its uncertainty of realizing a benefit from such losses. All of the Company’s operating losses since inception have been generated in the United States. A reconciliation of the federal statutory income tax rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2023 2022 U.S. federal statutory income tax rate 21.0% 21.0% LLC period net book loss —% (14.9%) Federal valuation allowance (22.4%) (5.9%) Tax credit carryforwards 1.6% —% Permanent items, including stock-based compensation (0.2%) (0.2%) Effective tax rate —% —% The principal components of the Company’s deferred tax assets and liabilities as of December 31, 2023 and 2022 were comprised as follows (in thousands): December 31, 2023 2022 Deferred tax assets: Capitalized research and development expenses $ 28,753 $ 3,462 Net operating loss carryforwards 5,483 261 Tax credit carryforwards 693 — Stock-based compensation expense 781 — Operating lease liability 114 106 Accrued expenses — 93 Other 61 32 Total deferred tax assets 35,885 3,954 Less: valuation allowance (34,040) (3,851) Net deferred tax assets 1,845 103 Deferred tax liabilities: Operating lease right-of-use asset (100) (103) Accretion (1,745) — Total deferred tax liabilities (1,845) (103) Net deferred taxes $ — $ — As of December 31, 2023, the Company had federal and state net operating loss (“NOL”) carryforwards of $16.7 million and $28.2 million respectively. Federal NOLs may be carried forward indefinitely. State NOLs expire at various dates from 2038 through 2043. As of December 31, 2023, the Company had federal research and development tax credit carryforwards of $0.7 million which expire in 2043. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are composed primarily of capitalized research and development expenses and net operating loss carryforwards. Management has considered the Company’s history of net losses incurred since inception and the probability of future losses to conclude it is more likely than not that the Company will not recognize the benefits of deferred tax assets. As a result, the Company has established a valuation allowance for the full amount of its net deferred tax assets as of December 31, 2023. The increase in the valuation allowance of $30.2 million during the year ended December 31, 2023 was primarily due to the additional operating loss generated by the Company. NOL and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50% as defined under Sections 382 and 383 in the Internal Revenue Code (“IRC”). This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the Company’s value immediately prior to the ownership change. As a result of ownership changes in the Company from its inception through December 31, 2023, the Company’s NOL and tax credit carryforwards allocable to the periods preceding each such ownership change could be subject to limitations under IRC Section 382, however the Company has not yet completed an IRC Section 382 study. The Company had no unrecognized tax benefits as of either December 31, 2023 or 2022. The Company has not conducted a study of its research and development credit carryforwards generated during any year. This study, once completed, may result in an adjustment to the Company’s research and development credit carryforwards. However, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credit carryforwards, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated statements of operations and comprehensive loss if an adjustment were required. The Company files income tax returns in the United States federal tax jurisdiction and various state jurisdictions. Since the Company is in a loss carryforward position, it is generally subject to examination by federal and state tax authorities for all tax years in which a loss carryforward is available.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Litigation From time to time, the Company may become subject to legal proceedings, claims and litigation arising in the ordinary course of business. From time to time, the Company may be involved in legal proceedings arising in the ordinary course of its business. Between July 25 and October 3, 2023, Talaris received eleven demand letters (the “Demands”) regarding the Proxy Statement (as defined below). In addition, three lawsuits were filed (captioned Wieder v. Talaris Therapeutics, Inc., et al., No. 1:23-cv-08355 (S.D.N.Y. filed Sept. 21, 2023), Carlisle v. Talaris Therapeutics, Inc., et al., No. 1:23-cv-08520 (S.D.N.Y. filed Sept. 27, 2023), and Roberts v. Talaris Therapeutics, Inc., et al., No. 1:23-cv-01063 (D. Del. filed Sept. 27, 2023)) (the “Lawsuits,” and together with the Demands, the “Actions”), in each case, by purported stockholders of Talaris challenging the proposed Reverse Merger and the disclosures in the definitive proxy statement filed by Talaris with the SEC on July 20, 2023, and as amended on August 25, 2023 and September 11, 2023 (the “Proxy Statement”). The Actions generally alleged that certain disclosures in the Proxy Statement were false or misleading and asserted claims against Talaris and its Board of Directors for violations of Sections 14(a) and 20(a) of the Exchange Act of 1934. The purported stockholders sought unspecified monetary damages and an award of costs and expenses, including reasonable attorney’s fees. On October 10, 2023, Talaris filed a Form 8-K to update and supplement the Proxy Statement, which contained certain additional disclosures relating to the Reverse Merger (the “Supplemental Disclosures”). Thereafter, plaintiffs in the Lawsuits voluntarily dismissed their complaints, and opposing counsel (for the stockholders in the Actions) requested a mootness fee in connection with the Supplemental Disclosures. The Reverse Merger subsequently closed on October 19, 2023. Thereafter, the parties engaged in a negotiation over payment of a potential mootness fee(s) to resolve all the fee demands. On February 13, 2024, the parties entered into an agreement, under which the Company agreed to pay a total of approximately $0.2 million to resolve all the fee demands and the stockholders released all claims in connection with the Reverse Merger. This amount was recognized as general and administrative expense by the Company during the year ended December 31, 2023 and has been included within “Accrued expenses and other current liabilities” on the consolidated balance sheet as of December 31, 2023. New York Office Lease During the year ended December 31, 2022, the Company entered into a non-cancelable operating lease for its corporate offices in New York, New York (the “New York Office Lease”). The lease expires on February 28, 2026. The Company provided the landlord of the New York Office Lease with a security deposit in the form of a $0.2 million letter of credit, which is recorded as restricted cash on the consolidated balance sheets as of December 31, 2023 and 2022. The Company recorded an ROU asset and corresponding lease liability related to the New York Office Lease on the consolidated balance sheets as of December 31, 2023 and 2022. As there was no rate implicit in the New York Office Lease, the Company estimated its incremental borrowing rate. Based on this analysis, the Company calculated a discount rate of 15.6% for the New York Office Lease. As of December 31, 2023, the future minimum lease payments due under the New York Office Lease are as follows (in thousands): Year Ending December 31, Amount 2024 $ 221 2025 227 2026 38 Total lease payments 486 Less: effect of discounting (71) Total operating lease liability $ 415

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2023
Retirement Benefits [Abstract]
401(k) Savings Plan	401(k) Savings Plan The Company implemented a defined-contribution savings plan under Section 401(k) of the IRC (the “401(k) Plan”) during the year ended December 31, 2023. The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation, subject to statutory limitations. The Company did not make any matching contributions to the 401(k) Plan during the year ended December 31, 2023.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions On October 1, 2021, and April 4, 2022, the Company entered into promissory note agreements with an equity investor, KVP Capital LP (“KVP”), for $0.2 million and $0.3 million aggregate principal amounts, payable on demand. The promissory notes were recorded at carrying value and did not bear interest. The issuance of the Series A convertible preferred units on April 18, 2022 triggered the repayment of the promissory notes. There was no gain or loss recognized upon the extinguishment of the promissory notes during the year ended December 31, 2022. In May 2023, an advisor affiliated with Fourth Avenue FF Opportunities LP – Series Z, previously a beneficial owner the Company’s outstanding capital stock, exercised stock options to purchase 75,782 shares of the Company’s common stock for $0.13 per share. The Company subsequently repurchased the shares from the advisor at $2.76 per share, equivalent to fair value as of the repurchase date, for an aggregate purchase price of $0.2 million. Fourth Avenue FF Opportunities LP – Series Z then purchased the shares from the Company at the same amount $2.76 per share for an aggregate purchase price of $0.2 million . As of December 31, 2023 and 2022, there were no amounts due to or from any related party.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share The following common stock equivalents have been excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive: December 31, 2023 2022 Series A convertible preferred stock — 2,163,764 Outstanding stock options under 2022 Equity Incentive Plan 1,403,409 374,282 Outstanding stock options under 2023 Equity Incentive Plan 1,042,291 — Unvested restricted stock units under 2023 Equity Incentive Plan 18,697 — Common stock subject to repurchase related to early exercised stock options 388,943 — Total 2,853,340 2,538,046

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events The Company has evaluated subsequent events for recognition and disclosure purposes through March 19, 2024, the filing date of this Annual Report on Form 10-K. Except for the matters described below, the Company has concluded that no other events or transactions have occurred that require disclosure in the consolidated financial statements. January 2024 Offering On January 25, 2024, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Jefferies LLC, Piper Sandler & Co., Guggenheim Securities, LLC and Truist Securities, Inc. (collectively, the “Underwriters”) in connection with the offering, issuance and sale by the Company of 4,615,384 shares of the Company’s common stock at a public offering price of $32.50 per share, less underwriting discounts and commissions, pursuant to an effective shelf registration statement on Form S-3 (Registration No. 333-266875). The Company granted the underwriters a 30-day option to purchase up to 692,307 shares of common stock at the public offering price, less the underwriting discounts and commissions, which was exercised by the Underwriters in full on January 25, 2024. The January 2024 Offering closed on January 29, 2024.

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and US GAAP, as found in the Accounting Standards Codification (“ASC”) of the Financial Accounting Standards Board (“FASB”).
Segment Information	Segment Information
Use of Estimates	Use of Estimates
Fair Value of Financial Instruments	Fair Value of Financial Instruments ASC Topic 820, Fair Value Measurement , (“ASC 820”) establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. • Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.
Cash Equivalents	Cash Equivalents Cash equivalents are highly-liquid investments that are readily convertible into cash with original maturities of three months or less when purchased. These assets include investments in money market funds that invest in U.S. Treasury and government agency obligations. Cash equivalents are reflected at fair value based on quoted market prices, as further described in Note 5, “Fair Value Measurements”.
Investments	Investments Investments consist of securities with original maturities greater than three months when purchased. Short-term investments consist of investments that are available for use in current operations. Long-term investments consist of investments with maturities of greater than one year that are not available for use in current operations. The Company did not maintain any long-term investments as of December 31, 2023 or 2022. The Company classifies all of its investments as available-for-sale securities. Accordingly, these investments are recorded at fair value. Realized gains and losses and amortization and accretion of discounts and premiums are included in “Other income, net”. Unrealized gains and losses on available-for-sale securities are included in “Accumulated other comprehensive income” as a component of stockholders’ equity (deficit) until realized. For available-for-sale debt securities in unrealized loss positions, the Company is required to assess whether to record an allowance for credit losses using an expected loss model. A credit loss is limited to the amount by which the amortized cost of an investment exceeds its fair value. A previously-recognized credit loss may be decreased in subsequent periods if the Company’s estimate of fair value for the investment increases. To determine whether to record a credit loss, the Company considers, among other factors, adverse conditions related to the security, industry, or geographic area, failure of the issuer to make scheduled payments, and changes in the issuer’s credit rating.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost and consist of computer and office equipment and leasehold improvements. The Company capitalizes property and equipment that is acquired for research and development activities and that has alternative future use. Expenditures for repairs and maintenance are recorded to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. Leasehold improvements are depreciated over the lesser of their useful lives or the term of the lease. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets when events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. Recoverability is measured by comparing the carrying value of the asset to the future undiscounted cash flows from the use and eventual disposition of the asset. If an asset is considered to be impaired, the impairment loss to be recognized is measured as the amount by which the carrying value of the asset exceeds its fair value.
Leases	Leases The Company accounts for leases pursuant to ASC Topic 842, Leases (“ASC 842”). Upon the adoption ASC 842, the Company elected to utilize certain practical expedients, which among other things, permit the Company to not separate lease and non-lease components. Additionally, the Company elected an accounting policy whereby it does not apply the recognition requirements of ASC 842 to short-term leases with a term of 12 months or less. The Company determines if an arrangement is or contains a lease by evaluating whether the arrangement conveys the right to use an identified asset and whether the Company obtains substantially all of the economic benefits from and has the ability to direct the use of the asset. If a lease is determined to exist, at the lease commencement date, the Company recognizes a lease liability and a right-of-use (“ROU”) asset representing its right to use the underlying asset over the lease term. The Company determines the lease term at the lease commencement date, with the lease term including periods covered by renewal options that are reasonably certain of being exercised and periods covered by termination options that are reasonably certain of not being exercised. The initial measurement of the lease liability is calculated on the basis of the present value of the remaining lease payments and the ROU asset is measured on the basis of this liability, adjusted by prepaid and accrued rent, lease incentives, and initial direct costs. The subsequent measurement of a lease is dependent on whether the lease is classified as an operating lease or a finance lease. Operating lease cost is recognized on a straight-line basis over the lease term, with the cost presented as a component of general and administrative expenses in the consolidated statements of operations and comprehensive loss. The Company has not recognized any financing leases to date. The Company’s lease requires other payments such as costs related to service components, real estate taxes, common area maintenance, and insurance. These costs are generally variable in nature and based on the actual costs incurred and required by the lease. As the Company has elected to not separate lease and non-lease components for all classes of underlying assets, all variable costs associated with the lease are expensed in the period incurred and presented and disclosed as variable lease costs. ASC 842 requires that a lessee use the rate implicit in the lease when measuring the lease liability and ROU asset, unless that rate is not readily determinable. When the rate implicit in the lease is not readily determinable, the Company uses its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of future lease payments. The Company gives consideration to the Company’s credit standing, the term of the lease, total lease payments and adjusts for the impacts of collateral, as necessary, when calculating its incremental borrowing rates.
Research and Development Expenses	Research and Development Expenses Expenditures relating to research and development are expensed as incurred. Research and development expenses include external expenses incurred under arrangements with third parties; consulting costs; salaries and personnel-related costs, including non-cash stock-based compensation expense; license fees to acquire in-process research and development that does not have an alternative future use and other expenses. Non-refundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. Where contingent milestone payments are due to third parties under research and development or license agreements, the milestone payment obligations are expensed when the related milestone events are achieved. As part of the process of preparing the consolidated financial statements, the Company is required to estimate its accrued research and development expenses as of each balance sheet date. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. This process involves reviewing open contracts, communicating with internal personnel to identify services that have been performed on the Company’s behalf and estimating the level of service performed and the associated cost incurred for the service when the Company has not yet been invoiced or otherwise notified of the actual cost. The Company periodically confirms the accuracy of its estimates with its service providers and makes adjustments if necessary. The majority of the Company’s service providers invoice monthly in arrears for services performed or when contractual milestones are met. The financial terms of agreements with these service providers are subject to negotiation, vary from contract-to-contract and may result in uneven payment flows. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense.
Intellectual Property Expenses	Intellectual Property Expenses The Company expenses legal costs related to patent applications as they are incurred. Such costs are classified as general and administrative expenses within the consolidated statements of operations and comprehensive loss.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based payments in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). This guidance requires all stock-based payments, including grants of stock options and restricted common units, to be recognized as expense in the consolidated statements of operations and comprehensive loss based on their grant date fair values. For stock options granted to employees, non-employees and members of the Company’s Board of Directors for their services on the Board of Directors, the Company estimates the grant date fair value of each stock option using the Black-Scholes option-pricing model. For stock-based payments subject to service-based vesting conditions, the Company recognizes stock-based compensation expense equal to the grant date fair value of stock-based payment on a straight-line basis over the requisite service period. Prior to the Company being publicly-traded, Legacy Tourmaline estimated the grant date fair value of its common stock using an appropriate valuation methodology, in accordance with the framework of the American Institute of Certified Public Accountants’ Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation . Each valuation methodology included estimates and assumptions that required the Company’s judgment. These estimates and assumptions included a number of objective and subjective factors, including external market conditions, guideline public company information, the prices at which the Company sold convertible preferred stock to third parties in arms’ length transactions, the rights and preferences of securities senior to the Company’s common stock at the time and the likelihood of achieving a liquidity event such as an initial public offering or sale. Significant changes to the assumptions used in the valuations could result in different fair values at each valuation date. In addition to the grant date fair value of the Company’s common stock, the Black‑Scholes option pricing model requires the input of certain subjective assumptions, including (i) the calculation of expected term of the stock-based payment, (ii) the risk‑free interest rate, (iii) the expected stock price volatility and (iv) the expected dividend yield. The Company uses the simplified method as prescribed by SEC Staff Accounting Bulletin No. 107 to calculate the expected term for stock options granted to employees as the Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The Company determines the risk‑free interest rate based on a treasury instrument whose term is consistent with the expected term of the stock options. Because the Company has only been publicly-traded for a short period of time, there is a lack of Company‑specific historical and implied volatility data. Accordingly, the Company bases its estimates of expected volatility on the historical volatility of a group of publicly-traded companies with similar characteristics to itself, including stage of product development and therapeutic focus within the life sciences industry. Historical volatility is calculated over a period of time commensurate with the expected term of the stock-based payment. The Company uses an assumed dividend yield of zero as the Company has never paid dividends on its common stock, nor does it expect to pay dividends on its common stock in the foreseeable future. The Company accounts for forfeitures of all stock-based payments when such forfeitures occur .
Income Taxes	Income Taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes , which provides for deferred taxes using an asset and liability approach. 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 financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. A valuation allowance against deferred tax assets is recorded if, based on the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions using a more-likely-than-not threshold for recognizing and resolving uncertain tax positions. The evaluation of uncertain tax positions is based on factors, including, but not limited to, changes in the law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, new audit activity and changes in facts or circumstances related to a tax position. Interest and penalty charges, if any, related to income taxes would be classified as a component of the “Provision for income taxes” in the consolidated statements of operations and comprehensive loss.
Net Loss per Share	Net Loss per Share Basic and diluted net loss per share attributable to common stockholders is presented in conformity with the two-class method required for participating securities. The Company considers its Series A convertible preferred stock and common stock issued subject to repurchase (related to early exercised stock options) to be participating securities. Net loss is attributed to common stockholders and participating securities based on their participation rights. Net loss attributable to common stockholders is not allocated to the Series A convertible preferred stock or common stock issued subject to repurchase as these holders do not have a contractual obligation to share in any losses. Under the two-class method, basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share attributable to common stockholders includes the effect, if any, from common stock issued subject to repurchase and the potential exercise or conversion of securities such as stock options and convertible preferred stock, which would result in the issuance of incremental shares of common stock. The Company has not adjusted its weighted average number of common shares outstanding in the calculation of diluted loss per share attributable to common stockholders as the Company reported a net loss for all periods presented and the effect of the aforementioned securities is anti-dilutive.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially expose the Company to concentrations of credit risk primarily consist of cash, cash equivalents and investments. Cash balances are deposited with federally-insured financial institutions in the United States and may, at times, exceed federally-insured limits. The Company maintains its cash, cash equivalents and investments with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. The Company’s cash equivalents are comprised of money market funds that are invested in U.S. Treasury and government agency obligations. The Company’s investments are comprised of commercial paper, government securities, and corporate debt securities. Credit risk in these securities is reduced as a result of the Company’s investment policy to limit the amount invested in any single issuer and to only invest in securities of a high credit quality.
Recently Adopted Accounting Pronouncements and Yet to be Adopted	Recently Adopted Accounting Pronouncements In June 2016, the FASB issued Accounting Standards Update (“ASU”) 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . This standard requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and it establishes additional disclosure requirements related to credit risks. For available-for-sale debt securities with expected credit losses, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. This guidance was originally effective for annual reporting periods beginning after December 15, 2020 and interim periods within fiscal years beginning after December 31, 2021, and early adoption was permitted. In November 2019, the FASB subsequently issued ASU 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates , whereby the effective date of this standard was deferred to annual reporting periods beginning after December 15, 2022, including interim periods within those annual reporting periods, and early adoption is still permitted. Accordingly, the Company adopted this new standard effective January 1, 2023, and the adoption of ASU 2016-13 did not have an impact on the consolidated financial statements. Recent Accounting Pronouncements - Yet to be Adopted In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures . This guidance is intended to improve reportable segment disclosure requirements through enhanced disclosures as well as clarify that entities with a single reportable segment are subject to new and existing segment reporting requirements. This guidance is effective for annual periods in fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. Entities must apply this guidance on a retrospective basis. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statements. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures

Reverse Merger (Tables)

Reverse Merger (Tables)	12 Months Ended
	Dec. 31, 2023
Reverse Recapitalization [Abstract]
Schedule Of Reverse Capitalization	The Company acquired the following assets and liabilities as part of the Reverse Merger (in thousands): Amount Cash and cash equivalents $ 392 Short-term investments 65,515 Prepaid expenses and other current assets 4,254 Accounts payable (726) Accrued expenses (543) Net assets acquired $ 68,892

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis	Assets measured at fair value on a recurring basis as of December 31, 2023 were as follows (in thousands): Total Level 1 Level 2 Level 3 Money market funds, included in cash and cash equivalents $ 4,604 $ 4,604 $ — $ — Short-term investments: Commercial paper 32,555 — 32,555 — Government securities 26,724 7,907 18,817 — Corporate debt securities 2,947 — 2,947 — Total $ 66,830 $ 12,511 $ 54,319 $ —

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Debt Securities, Available-for-Sale	Cash equivalents and short-term investments as of December 31, 2023 were comprised as follows (in thousands): Amortized Cost Unrealized Gains Unrealized Losses Fair Value Money market funds, included in cash and cash equivalents $ 4,604 $ — $ — $ 4,604 Short-term investments: Commercial paper 32,515 44 (4) 32,555 Government securities 26,703 25 (4) 26,724 Corporate debt securities 2,941 6 — 2,947 Total $ 66,763 $ 75 $ (8) $ 66,830

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property and equipment, net as of December 31, 2023 and 2022 was comprised as follows (in thousands): Estimated Useful Life December 31, 2023 2022 Leasehold improvements Shorter of useful life or remaining lease term $ 74 $ 64 Computer and office equipment 3 years 49 23 Total property and equipment, gross 123 87 Less: accumulated depreciation (38) (6) Total property and equipment, net $ 85 $ 81

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2023
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued expenses and other current liabilities as of December 31, 2023 and 2022 were comprised as follows (in thousands): December 31, 2023 2022 Accrued bonus $ 1,994 $ 446 Accrued clinical and manufacturing costs 438 185 Accrued consulting fees 692 81 Accrued legal fees 237 54 Other accrued expenses and other current liabilities 349 34 Total accrued expenses and other current liabilities $ 3,710 $ 800

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2023
Equity [Abstract]
Schedule of Stock by Class	As of December 31, 2023 and 2022, the Company had reserved for future issuance the following number of shares of common stock: December 31, 2023 2022 Conversion of outstanding Series A convertible preferred stock — 2,163,764 Exercises of outstanding stock options under 2022 Equity Incentive Plan 1,403,409 404,673 Exercises of outstanding stock options under 2023 Equity Incentive Plan 1,042,291 — Vesting of restricted stock units under 2023 Equity Incentive Plan 19,113 — Common stock subject to repurchase related to early exercised stock options 388,943 — Future issuances under 2022 Equity Incentive Plan — 353,142 Future issuances under 2023 Equity Incentive Plan 971,444 — Future issuances under 2023 Employee Stock Purchase Plan 203,367 — Total shares reserved for future issuance 4,028,567 2,921,579

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount	Total stock-based compensation expense recognized in the consolidated statements of operations and comprehensive loss for the years ended December 31, 2023 and 2022 was as follows (in thousands): Year Ended December 31, 2023 2022 Research and development $ 2,322 $ 165 General and administrative 3,447 30 Total stock-based compensation expense $ 5,769 $ 195
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions	The estimated grant-date fair value of the Company’s stock options was calculated using the Black-Scholes option pricing model, based on the following assumptions: Year Ended December 31, 2023 2022 Risk-free interest rate 3.4% – 4.8% 3.7% – 4.4% Dividend yield —% —% Volatility 82.2% – 86.1% 83.1% – 86.3% Expected term (in years) 5.5 – 6.1 3.3 – 6.1
Share-Based Payment Arrangement, Option, Activity	The following table summarizes changes in stock option activity during the year ended December 31, 2023: Options Weighted- Weighted- Aggregate Intrinsic Value Outstanding as of December 31, 2022 404,673 $ 0.14 7.2 $ 1,722 Granted 2,736,169 $ 8.33 Exercised (695,142) $ 0.21 Cancelled — $ — Outstanding as of December 31, 2023 2,445,700 $ 9.29 9.6 $ 41,320 Exercisable as of December 31, 2023 23,896 $ 11.02 9.7 $ 362
Share-Based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity	The following table summarizes changes in restricted stock unit activity during the year ended December 31, 2023: Shares Weighted- Unvested as of December 31, 2022 — $ — Granted 19,943 11.89 Vested (830) 11.89 Cancelled — — Unvested as of December 31, 2023 19,113 $ 11.89

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of the federal statutory income tax rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2023 2022 U.S. federal statutory income tax rate 21.0% 21.0% LLC period net book loss —% (14.9%) Federal valuation allowance (22.4%) (5.9%) Tax credit carryforwards 1.6% —% Permanent items, including stock-based compensation (0.2%) (0.2%) Effective tax rate —% —%
Schedule of Deferred Tax Assets and Liabilities	The principal components of the Company’s deferred tax assets and liabilities as of December 31, 2023 and 2022 were comprised as follows (in thousands): December 31, 2023 2022 Deferred tax assets: Capitalized research and development expenses $ 28,753 $ 3,462 Net operating loss carryforwards 5,483 261 Tax credit carryforwards 693 — Stock-based compensation expense 781 — Operating lease liability 114 106 Accrued expenses — 93 Other 61 32 Total deferred tax assets 35,885 3,954 Less: valuation allowance (34,040) (3,851) Net deferred tax assets 1,845 103 Deferred tax liabilities: Operating lease right-of-use asset (100) (103) Accretion (1,745) — Total deferred tax liabilities (1,845) (103) Net deferred taxes $ — $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Lessee, Operating Lease, Liability, to be Paid, Maturity	As of December 31, 2023, the future minimum lease payments due under the New York Office Lease are as follows (in thousands): Year Ending December 31, Amount 2024 $ 221 2025 227 2026 38 Total lease payments 486 Less: effect of discounting (71) Total operating lease liability $ 415

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following common stock equivalents have been excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive: December 31, 2023 2022 Series A convertible preferred stock — 2,163,764 Outstanding stock options under 2022 Equity Incentive Plan 1,403,409 374,282 Outstanding stock options under 2023 Equity Incentive Plan 1,042,291 — Unvested restricted stock units under 2023 Equity Incentive Plan 18,697 — Common stock subject to repurchase related to early exercised stock options 388,943 — Total 2,853,340 2,538,046

Nature of Business (Details)

Nature of Business (Details) $ in Millions		1 Months Ended
	Oct. 19, 2023 USD ($) shares	Jan. 31, 2024 USD ($)	Dec. 31, 2023 USD ($) shares	Dec. 31, 2022 shares
Class of Stock [Line Items]
Stock split ratio, common stock	0.1
Exchange ratio	0.07977
Common stock, shares, issued (in shares) | shares	20,336,741		20,337,571	867,499
Cash, cash equivalents and investments | $			$ 203
Private Placement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares) | shares	4,092,035
Consideration received on transaction | $	$ 75
January 2024 Offering | Subsequent Event
Class of Stock [Line Items]
Consideration received on transaction | $		$ 161.3
Common Stock
Class of Stock [Line Items]
Stock issued during period, shares, new issues (in shares) | shares	15,877,090

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2023 segment
Accounting Policies [Abstract]
Number of operating segments	1

Reverse Merger - Narrative (Det

Reverse Merger - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Oct. 19, 2023	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Reverse Recapitalization [Line Items]
Stock-based compensation expenses	$ 2,900	$ 5,769	$ 195
Payment of reverse merger costs	6,100	6,107	0
Goodwill	0
Intangible assets	0
Research and development
Schedule Of Reverse Recapitalization [Line Items]
Stock-based compensation expenses	1,400	2,322	165
General and administrative
Schedule Of Reverse Recapitalization [Line Items]
Stock-based compensation expenses	$ 1,500	$ 3,447	$ 30

Reverse Merger - Schedule Of Ne

Reverse Merger - Schedule Of Net Assets Acquired (Details) $ in Thousands	Oct. 19, 2023 USD ($)
Reverse Recapitalization [Abstract]
Cash and cash equivalents	$ 392
Short-term investments	65,515
Prepaid expenses and other current assets	4,254
Accounts payable	(726)
Accrued expenses	(543)
Net assets acquired	$ 68,892

Pfizer License Agreement (Detai

Pfizer License Agreement (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended	12 Months Ended
	May 02, 2023	May 03, 2022	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense				$ 32,368	$ 17,526
Pfizer License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment		$ 5,000
Consideration transferred					$ 12,100
Royalty rate payment		15%
Expected timing satisfaction, period		12 years
Maximum payment on the timing of transaction		$ 20,000
Pfizer License Agreement | Development and Regulatory Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contingent consideration, liability		128,000
Pfizer License Agreement | Sales Milestones
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contingent consideration, liability		$ 525,000
Series A Convertible Preferred Units | Pfizer License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares issued under license agreement (in shares)		7,125,000
Shares issued, price per share (usd per share)		$ 1
Equity interest issued and issuable		$ 7,100
Series A Convertible Preferred Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense			$ 8,800
Series A Convertible Preferred Stock | Pfizer License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares issued under license agreement (in shares)		7,125,000
Issuance of Series A convertible preferred stock pursuant to anti-dilution provision of license agreement with Pfizer Inc. (in shares)	8,823,529
Research and development expense	$ 8,800
Series A Convertible Preferred Stock | Pfizer Inc. | Pfizer License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Interest percent		15%

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value, Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash and cash equivalents		$ 0
Fair Value	$ 66,830	$ 0
Total	66,830
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	32,555
Government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	26,724
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2,947
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	12,511
Level 1 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0
Level 1 | Government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	7,907
Level 1 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	54,319
Level 2 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	32,555
Level 2 | Government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	18,817
Level 2 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2,947
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	0
Level 3 | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0
Level 3 | Government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0
Level 3 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0
Money market funds, included in cash and cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash and cash equivalents	4,604
Money market funds, included in cash and cash equivalents | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash and cash equivalents	4,604
Money market funds, included in cash and cash equivalents | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash and cash equivalents	0
Money market funds, included in cash and cash equivalents | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash and cash equivalents	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Cash and cash equivalents, fair value disclosure		$ 0
Investments	$ 66,830	0
Liabilities, fair value disclosure	$ 0	$ 0

Investments - Debt Securities,

Investments - Debt Securities, Available-for-Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	$ 66,763
Unrealized Gains	75
Unrealized Losses	(8)
Fair Value	66,830	$ 0
Money market funds, included in cash and cash equivalents | Cash and Cash Equivalents
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	4,604
Unrealized Gains	0
Unrealized Losses	0
Fair Value	4,604
Commercial paper
Schedule of Held-to-Maturity Securities [Line Items]
Fair Value	32,555
Commercial paper | Short-Term Investments
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	32,515
Unrealized Gains	44
Unrealized Losses	(4)
Fair Value	32,555
Government securities
Schedule of Held-to-Maturity Securities [Line Items]
Fair Value	26,724
Government securities | Short-Term Investments
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	26,703
Unrealized Gains	25
Unrealized Losses	(4)
Fair Value	26,724
Corporate debt securities
Schedule of Held-to-Maturity Securities [Line Items]
Fair Value	2,947
Corporate debt securities | Short-Term Investments
Schedule of Held-to-Maturity Securities [Line Items]
Amortized Cost	2,941
Unrealized Gains	6
Unrealized Losses	0
Fair Value	$ 2,947

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Investments	$ 66,830	$ 0
Cash and cash equivalents, fair value disclosure		$ 0
Unrealized loss position, less than 12 months	49,300
Unrealized loss position, more than 12 months	$ 0

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 123	$ 87
Less: accumulated depreciation	(38)	(6)
Total property and equipment, net	85	81
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 74	$ 64
Computer and office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	3 years	3 years
Total property and equipment, gross	$ 49	$ 23

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued bonus	$ 1,994	$ 446
Accrued clinical and manufacturing costs	438	185
Accrued consulting fees	692	81
Accrued legal fees	237	54
Other accrued expenses and other current liabilities	349	34
Total accrued expenses and other current liabilities	$ 3,710	$ 800

Convertible Preferred Stock (De

Convertible Preferred Stock (Details) $ / shares in Units, $ in Thousands			3 Months Ended	12 Months Ended
	May 02, 2023 USD ($) $ / shares shares	Apr. 18, 2022 USD ($) $ / shares shares	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Sep. 02, 2022 $ / shares shares	May 03, 2022 shares	Dec. 31, 2021 shares
Class of Stock [Line Items]
Convertible preferred stock, shares authorized (in shares)				0	27,125,000
Convertible preferred stock, par value ( usd per share) | $ / shares				$ 0.0001	$ 0.0001
Research and development expense | $				$ 32,368	$ 17,526
Conversion of convertible preferred stock to common stock in connection with reverse merger (in shares)				10,222,414
Convertible preferred stock, shares outstanding (in shares)				0	27,125,000
Undesignated preferred stock, shares authorized (in shares)				10,000,000	0
Shares outstanding (in shares)				0	0
Stock issued (in shares)				0	0
Series A Convertible Preferred Units
Class of Stock [Line Items]
Conversion ratio		1
Convertible preferred stock, shares outstanding (in shares)				0	0			0
Series A Convertible Preferred Units | Pfizer License Agreement
Class of Stock [Line Items]
Shares issued under license agreement (in shares)							7,125,000
Series A Convertible Preferred Units | Initial Series A Securities Purchase Agreement
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)		20,000,000
Price per share (usd per share) | $ / shares		$ 1
Consideration received on transaction | $		$ 20,000
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Conversion ratio						1
Convertible preferred stock, shares authorized (in shares)						27,125,000
Convertible preferred stock, par value ( usd per share) | $ / shares						$ 0.0001
Research and development expense | $			$ 8,800
Convertible preferred stock, shares outstanding (in shares)				0	27,125,000			0
Series A Convertible Preferred Stock | Pfizer License Agreement
Class of Stock [Line Items]
Shares issued under license agreement (in shares)							7,125,000
Issuance of Series A convertible preferred stock pursuant to anti-dilution provision of license agreement with Pfizer Inc. (in shares)	8,823,529
Research and development expense | $	$ 8,800
Series A Convertible Preferred Stock | Series A Extension
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	92,200,000
Price per share (usd per share) | $ / shares	$ 1
Consideration received on transaction | $	$ 92,200

Common Stock - Narrative (Detai

Common Stock - Narrative (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) vote shares	Dec. 31, 2022 shares	Sep. 02, 2022	May 03, 2022 shares
Class of Stock [Line Items]
Common unit, outstanding (in shares)				6.39697802
Common stock, conversion ratio			1
Common stock, shares authorized (in shares)	140,000,000	50,000,000
Number of votes for each share of common stock | vote	1
Dividends, common stock | $	$ 0
Nonvoting Common Stock
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	10,000,000

Common Stock - Schedule of Shar

Common Stock - Schedule of Shares Reserved For Future Issuance (Details) - shares	Dec. 31, 2023	Oct. 17, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	4,028,567		2,921,579
2022 Equity Incentive Plan
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	0		353,142
2023 Equity Incentive Plan
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	971,444	2,033,677	0
2023 ESPP
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	203,367		0
Restricted Stock Units (RSUs)
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	19,113		0
Common stock subject to repurchase related to early exercised stock options
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	388,943		0
Employee Stock Option | 2022 Equity Incentive Plan
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	1,403,409		404,673
Employee Stock Option | 2023 Equity Incentive Plan
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	1,042,291		0
Series A convertible preferred stock
Class of Stock [Line Items]
Shares reserved for future issuance (in shares)	0		2,163,764

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Oct. 17, 2023 shares	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)		4,028,567	2,921,579
Share-based compensation arrangement by share-based payment award, fair value assumptions, weighted average fair value of common stock (usd per share) | $ / shares			$ 4.39
Share-based compensation arrangement by share-based payment award, options, grants in period, weighted average grant date fair value (usd per share) | $ / shares		$ 6.60	$ 4.26
Share-based compensation arrangement by share-based payment award, options, exercises in period, intrinsic value | $		$ 1,800
Share-based compensation arrangement by share-based payment award, options, exercises in period (in shares)		695,142	0
Share-based payment arrangement, nonvested award, option, cost not yet recognized, amount | $		$ 16,800
Proceeds from stock options exercised | $		144	$ 0
Deferred compensation share-based arrangements, liability, current | $		$ 100
Employee Stock Option
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, fair value assumptions, weighted average fair value of common stock (usd per share) | $ / shares		$ 8.33
Share-based payment arrangement, nonvested award, cost not yet recognized, period for recognition		3 years 6 months
Restricted Stock Units (RSUs)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)		19,113	0
Share-based payment arrangement, nonvested award, cost not yet recognized, period for recognition		3 years 8 months 12 days
Share-based compensation arrangement by share-based payment award, equity instruments other than options, vested in period, fair value | $		$ 100
Share-based payment arrangement, nonvested award, excluding option, cost not yet recognized, amount | $		$ 200
Common stock subject to repurchase related to early exercised stock options
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)		388,943	0
Share-based compensation arrangement by share-based payment award, options, exercises in period (in shares)		647,386	0
Share-based compensation arrangement by share-based payment award, repurchase of options, period		6 months
Share-based compensation arrangement by share-based payment award, options, nonvested, number of shares (in shares)		388,943
2023 Equity Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)	2,033,677	971,444	0
Share-based compensation arrangement by share-based payment award, number of annual increase of shares authorized, period	10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Percentage of Outstanding Stock Maximum	5%
Share-based compensation arrangement by share-based payment award, maximum number of shares authorized, multiple of share reserve	3
2023 Equity Incentive Plan | Employee Stock Option
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, expiration period	10 years
Shares reserved for future issuance (in shares)		1,042,291	0
2023 ESPP
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares reserved for future issuance (in shares)		203,367	0
2023 ESPP | Employee Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of annual increase of shares authorized, period	10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Percentage of Outstanding Stock Maximum	1%
Share-based compensation arrangement by share-based payment award, number of shares authorized (in shares)	203,367
Share-based compensation arrangement by share-based payment award, maximum number of shares authorized, multiple of share reserve	3

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands		12 Months Ended
	Oct. 19, 2023	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	$ 2,900	$ 5,769	$ 195
Research and development
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	1,400	2,322	165
General and administrative
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,500	$ 3,447	$ 30

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Valuation Assumptions (Details) - Employee Stock Option	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Risk-free interest rate (minimum)	3.40%	3.70%
Risk-free interest rate (maximum)	4.80%	4.40%
Dividend yield	0%	0%
Volatility (minimum)	82.20%	83.10%
Volatility (maximum)	86.10%	86.30%
Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	3 years 3 months 18 days
Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Options
Beginning balance, outstanding (in shares)	404,673
Granted (in shares)	2,736,169
Exercised (in shares)	(695,142)	0
Cancelled (in shares)	0
Ending balance, outstanding (in shares)	2,445,700	404,673
Exercisable (in shares)	23,896
Weighted- Average Exercise Price
Beginning balance, outstanding (usd per share)	$ 0.14
Granted (usd per share)	8.33
Exercised (usd per share)	0.21
Cancelled (usd per share)	0
Ending balance, outstanding (usd per share)	9.29	$ 0.14
Exercisable (usd per share)	$ 11.02
Stock Options Additional Disclosures
Weighted average remaining contractual term, outstanding	9 years 7 months 6 days	7 years 2 months 12 days
Weighted average remaining contractual term, exercisable	9 years 8 months 12 days
Aggregate intrinsic value, outstanding	$ 41,320	$ 1,722
Aggregate intrinsic value, exercisable	$ 362

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Shares
Beginning balance, unvested, outstanding (in shares) | shares	0
Granted (in shares) | shares	19,943
Vested (in shares) | shares	(830)
Forfeited (in shares) | shares	0
Ending balance, unvested, outstanding (in shares) | shares	19,113
Weighted- Average Grant Date Fair Value per Share
Beginning balance, unvested (usd per share) | $ / shares	$ 0
Granted (usd per share) | $ / shares	11.89
Vested (usd per share) | $ / shares	11.89
Cancelled (usd per share) | $ / shares	0
Ending balance, unvested (usd per share) | $ / shares	$ 11.89

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating Loss Carryforwards [Line Items]
Income tax expense (benefit)	$ 0	$ 0
Tax credit carryforward	700,000
Increase (decrease) in valuation allowance	30,200,000
Unrecognized tax benefits	0	$ 0
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	16,700,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 28,200,000

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax rate	21%	21%
LLC period net book loss	0%	(14.90%)
Federal valuation allowance	(22.40%)	(5.90%)
Tax credit carryforwards	1.60%	0%
Permanent items, including stock-based compensation	(0.20%)	(0.20%)
Effective tax rate	0%	0%

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Capitalized research and development expenses	$ 28,753	$ 3,462
Net operating loss carryforwards	5,483	261
Tax credit carryforwards	693	0
Stock-based compensation expense	781	0
Operating lease liability	114	106
Accrued expenses	0	93
Other	61	32
Total deferred tax assets	35,885	3,954
Less: valuation allowance	(34,040)	(3,851)
Net deferred tax assets	1,845	103
Deferred tax liabilities:
Operating lease right-of-use asset	(100)	(103)
Accretion	(1,745)	0
Total deferred tax liabilities	(1,845)	(103)
Net deferred taxes	$ 0	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) $ in Millions		2 Months Ended	12 Months Ended
	Feb. 13, 2024 USD ($)	Oct. 03, 2023 letter lawsuit	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Loss Contingencies [Line Items]
Demand letters | letter		11
Number of lawsuits | lawsuit		3
Security deposit			$ 0.2	$ 0.2
Company calculated discount rate			15.60%
Operating lease expense			$ 0.2	0.1
Operating lease, payments			0.2
Short-term lease, cost			0	0
Variable lease, cost			$ 0	$ 0
Remaining lease term			2 years 2 months 12 days
Subsequent Event
Loss Contingencies [Line Items]
Litigation settlement	$ 0.2

Commitments and Contingencies_2

Commitments and Contingencies - Lessee, Operating Lease, Liability, to be Paid, Maturity (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2024	$ 221
2025	227
2026	38
Total lease payments	486
Less: effect of discounting	(71)
Total operating lease liability	$ 415

401(k) Savings Plan (Details)

401(k) Savings Plan (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Retirement Benefits [Abstract]
Define contribution plan	$ 0

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended	12 Months Ended
	Jun. 01, 2023	May 31, 2023	May 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Apr. 04, 2022	Oct. 01, 2021
Related Party Transaction [Line Items]
Share-based compensation arrangement by share-based payment award, options, exercises in period (in shares)				695,142	0
Exercised (usd per share)				$ 0.21
Shares acquired, average cost per share (usd per share)		$ 2.76
Treasury stock, value, acquired, cost method	$ 0.2
Investor | KVP Capital LP Promissory Note
Related Party Transaction [Line Items]
Debt instrument, face amount						$ 0.3	$ 0.2
Gain (loss) on extinguishment of debt					$ 0
Affiliated Entity
Related Party Transaction [Line Items]
Share-based compensation arrangement by share-based payment award, options, exercises in period (in shares)			75,782
Exercised (usd per share)		$ 0.13

Net Loss per Share (Details)

Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	2,853,340	2,538,046
Series A convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	0	2,163,764
Employee Stock Option | 2022 Equity Incentive Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	1,403,409	374,282
Employee Stock Option | 2023 Equity Incentive Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	1,042,291	0
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	18,697	0
Common stock subject to repurchase related to early exercised stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	388,943	0

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent Event - USD ($) $ / shares in Units, $ in Millions		1 Months Ended
	Jan. 25, 2024	Jan. 31, 2024
Underwriting Agreement
Subsequent Event [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	4,615,384
Price per share (usd per share)	$ 32.50
Over-Allotment Option
Subsequent Event [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	692,307
Maximum number of shares available for underwriters (in shares)	30
January 2024 Offering
Subsequent Event [Line Items]
Gross proceeds from issuance initial public offering		$ 172.5
Consideration received on transaction		$ 161.3