Apogee Therapeutics (APGE) 10-Q 13 Nov 23 2023 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Nov. 06, 2023
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2023
Entity File Number	001-41740
Entity Registrant Name	Apogee Therapeutics, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	88-0588063
Entity Address, Address Line One	221 Crescent St.
Entity Address, Address Line Two	Building 17
Entity Address, Address Line Three	Suite 102b
Entity Address, City or Town	Waltham
Entity Address State Or Province	MA
Entity Address, Postal Zip Code	02453
City Area Code	650
Local Phone Number	394-5230
Title of 12(b) Security	Common Stock, par value $0.00001 per share
Trading Symbol	APGE
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Central Index Key	0001974640
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Amendment Flag	false
Voting Common Stock
Entity Common Stock, Shares Outstanding		37,187,654
Nonvoting Common Stock
Entity Common Stock, Shares Outstanding		13,486,642

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 188,269	$ 151,890
Marketable securities	234,585
Prepaid expenses and other current assets	3,567	165
Total current assets	426,421	152,055
Total assets	426,421	152,055
Current liabilities:
Accounts payable	1,208	418
Accrued expenses	15,970	9,562
Total current liabilities	17,178	9,980
Total liabilities	17,178	9,980
Commitments and contingencies (Note 8)
Preferred Units		177,467
Stockholders' equity/members' deficit:
Common Units; no units authorized, issued and outstanding at September 30, 2023; 5,000,000 units authorized, issued and outstanding as of December 31, 2022		2,251
Incentive Units; no units authorized, issued and outstanding at September 30, 2023; 12,412,473 units authorized, 9,648,374 issued and 1,625,086 outstanding as of December 31, 2022		2,142
Preferred Stock; 10,000,000 authorized, $0.00001 par value, no shares issued and outstanding September 30, 2023; No shares authorized, issued and outstanding at December 31, 2022
Additional paid-in capital	501,143
Accumulated other comprehensive income	135
Accumulated deficit	(92,035)	(39,785)
Total stockholders' equity/members' deficit	409,243	(35,392)
Total liabilities, preferred units and stockholders' equity/members' deficit	$ 426,421	152,055
Series A Preferred Units
Current liabilities:
Preferred Units		28,971
Series B Preferred Units
Current liabilities:
Preferred Units		$ 148,496

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Preferred Units, units authorized		65,089,212
Preferred Units, units issued		65,089,212
Preferred Units, units outstanding		65,089,212
Preferred Units, liquidation value		$ 169,000
Common Units, units authorized	0	5,000,000
Common Units, units issued	5,000,000	5,000,000
Common Units, units outstanding	5,000,000	5,000,000
Incentive Units, units authorized	0	12,412,473
Incentive Units, units issued	0	9,648,374
Incentive Units, units outstanding	0	1,625,086
Preferred stock, shares authorized	10,000,000	0
Preferred stock, par value	$ 0.00001
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, shares authorized	400,000,000	0
Common stock, par value	$ 0.00001
Common stock, shares, issued	50,674,296	0
Common stock, shares outstanding	48,017,621	0
Series A Preferred Units
Preferred Units, units authorized	0	20,000,000
Preferred Units, units issued	20,000,000	20,000,000
Preferred Units, units outstanding	20,000,000	20,000,000
Series B Preferred Units
Preferred Units, units authorized	0	45,089,212
Preferred Units, units issued	45,089,212	45,089,212
Preferred Units, units outstanding	45,089,212	45,089,212

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENT OF OPERATIONS (UNAUDITED) - USD ($) $ in Thousands		3 Months Ended		8 Months Ended	9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2023
Operating expenses:
Research and development	[1]	$ 17,069	$ 9,885	$ 15,578	$ 39,470
General and administrative	[2]	7,236	622	1,050	16,378
Total operating expenses		24,305	10,507	16,628	55,848
Loss from operations		(24,305)	(10,507)	(16,628)	(55,848)
Other income (expense), net:
Interest income		3,465			3,598
Other financing expense			(9,150)	(9,150)
Total other income (expense), net		3,465	(9,150)	(9,150)	3,598
Net loss		$ (20,840)	$ (19,657)	$ (25,778)	$ (52,250)
Net loss per unit, basic		$ (0.51)	$ (9.46)	$ (17)	$ (3.04)
Net loss per unit, diluted		$ (0.51)	$ (9.46)	$ (17)	$ (3.04)
Weighted-average common units outstanding, basic		41,231,379	2,078,804	1,516,736	17,209,842
Weighted-average common units outstanding, diluted		41,231,379	2,078,804	1,516,736	17,209,842
[1] Includes related-party amounts of $6,624 for the three months ended September 30, 2023, $9,596 for the three months ended September 30, 2022, $21,083 for the nine months ended September 30, 2023 and $15,219 for the period from February 4, 2022 (inception) to September 30, 2022. Includes related-party amounts of $9 for the three months ended September 30, 2023, none for the three months ended September 30, 2022, $53 for the nine months ended September 30, 2023 and $273 for the period from February 4, 2022 (inception) to September 30, 2022.

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENT OF OPERATIONS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands		3 Months Ended		8 Months Ended	9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2023
Research and development	[1]	$ 17,069	$ 9,885	$ 15,578	$ 39,470
General and administrative	[2]	7,236	622	1,050	16,378
Related Party
Research and development		6,624	9,596	15,219	21,083
General and administrative		$ 9	$ 0	$ 273	$ 53
[1] Includes related-party amounts of $6,624 for the three months ended September 30, 2023, $9,596 for the three months ended September 30, 2022, $21,083 for the nine months ended September 30, 2023 and $15,219 for the period from February 4, 2022 (inception) to September 30, 2022. Includes related-party amounts of $9 for the three months ended September 30, 2023, none for the three months ended September 30, 2022, $53 for the nine months ended September 30, 2023 and $273 for the period from February 4, 2022 (inception) to September 30, 2022.

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE LOSS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		8 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2023
CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE LOSS (UNAUDITED)
Net Income (Loss)	$ (20,840)	$ (19,657)	$ (25,778)	$ (52,250)
Change in unrealized gains on marketable securities, net of tax	135			135
Comprehensive loss	$ (20,705)	$ (19,657)	$ (25,778)	$ (52,115)

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENT OF PREFERRED UNITS AND STOCKHOLDERS' EQUITY/MEMBERS' DEFICIT (UNAUDITED) - USD ($) $ in Thousands	Series A Preferred Units	Series B Preferred Units	COMMON UNITS	INCENTIVE UNITS	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED DEFICIT	ACCUMULATED OTHER COMPREHENSIVE INCOME	Total
Beginning balance at Feb. 03, 2022	$ 0	$ 0
Beginning balance (in shares) at Feb. 03, 2022	0	0
Ending balance at Mar. 31, 2022	$ 3,771
Ending balance (in shares) at Mar. 31, 2022	5,000,000,000
Beginning balance at Feb. 03, 2022							$ 0		$ 0
Beginning balance (in shares) at Feb. 03, 2022	0	0
MEMBERS' DEFICIT
Net Income (Loss)							(4,305)		(4,305)
Ending balance at Mar. 31, 2022			$ 1,688				(4,305)		(2,617)
Ending balance (in shares) at Mar. 31, 2022			1,250,000,000
Beginning balance at Feb. 03, 2022	$ 0	$ 0
Beginning balance (in shares) at Feb. 03, 2022	0	0
PREFERRED UNITS
Issuance of Series A Preferred Units initial closing, net of a net tranche option liability of $1,050 and issuance costs of $179	$ 3,771
Issuance of Series A Preferred Unitsinitial closing, net of a net tranche option liability of $1,050 and issuance costs of $179 (in shares)	5,000,000
Ending balance at Jun. 30, 2022	$ 3,771
Ending balance (in shares) at Jun. 30, 2022	5,000,000
Beginning balance at Feb. 03, 2022							0		0
Beginning balance (in shares) at Feb. 03, 2022	0	0
MEMBERS' DEFICIT
Issuance of Common Units in payment of option fee			$ 1,688						1,688
Common stock issued in IPO, net of issuance costs of $29,666			$ 1,688						1,688
Issuance of Common Units in payment of option fee (in shares)			1,250,000
Common stock issued in IPO, net of issuance costs of $29,666 (in shares)			1,250,000
Ending balance at Jun. 30, 2022			$ 1,688				(6,121)		(4,433)
Ending balance (in shares) at Jun. 30, 2022			1,250,000
Beginning balance at Feb. 03, 2022	$ 0	$ 0
Beginning balance (in shares) at Feb. 03, 2022	0	0
Ending balance at Sep. 30, 2022	$ 8,171
Ending balance (in shares) at Sep. 30, 2022	10,000,000,000
Beginning balance at Feb. 03, 2022							0		0
Beginning balance (in shares) at Feb. 03, 2022	0	0
MEMBERS' DEFICIT
Net Income (Loss)									(25,778)
Ending balance at Sep. 30, 2022			$ 1,688				(25,778)		(24,090)
Ending balance (in shares) at Sep. 30, 2022			2,500,000,000
Beginning balance at Mar. 31, 2022	$ 3,771
Beginning balance (in shares) at Mar. 31, 2022	5,000,000,000
Ending balance at Jun. 30, 2022	$ 3,771
Ending balance (in shares) at Jun. 30, 2022	5,000,000
Beginning balance at Mar. 31, 2022			$ 1,688				(4,305)		(2,617)
Beginning balance (in shares) at Mar. 31, 2022	5,000,000,000
Beginning balance (in shares) at Mar. 31, 2022			1,250,000,000
MEMBERS' DEFICIT
Net Income (Loss)							(1,816)		(1,816)
Ending balance at Jun. 30, 2022			$ 1,688				(6,121)		(4,433)
Ending balance (in shares) at Jun. 30, 2022			1,250,000
Beginning balance (in shares) at Jun. 30, 2022	5,000,000
PREFERRED UNITS
Issuance of Series A Preferred Units initial closing, net of a net tranche option liability of $1,050 and issuance costs of $179	$ 5,000,000
Issuance of Series A Preferred Unitsinitial closing, net of a net tranche option liability of $1,050 and issuance costs of $179 (in shares)	5,000,000
Reclassification of tranche rights upon issuance of preferred units	$ (600)
Ending balance at Sep. 30, 2022	$ 8,171
Ending balance (in shares) at Sep. 30, 2022	10,000,000,000
Beginning balance (in shares) at Jun. 30, 2022	5,000,000
MEMBERS' DEFICIT
Conversion of preferred, common, and incentive units into common stock (in shares)			1,250,000,000
Net Income (Loss)							(19,657)		(19,657)
Ending balance at Sep. 30, 2022			$ 1,688				(25,778)		(24,090)
Ending balance (in shares) at Sep. 30, 2022			2,500,000,000
Beginning balance at Dec. 31, 2022	$ 28,971	$ 148,496							$ 177,467
Beginning balance (in shares) at Dec. 31, 2022	20,000,000	45,089,212							65,089,212
Ending balance at Mar. 31, 2023	$ 28,971	$ 148,496
Ending balance (in shares) at Mar. 31, 2023	20,000,000	45,089,212
Beginning balance at Dec. 31, 2022			$ 2,251	$ 2,142			(39,785)		$ (35,392)
Beginning balance (in shares) at Dec. 31, 2022	20,000,000	45,089,212							65,089,212
Beginning balance (in shares) at Dec. 31, 2022			5,000,000	1,625,086
MEMBERS' DEFICIT
Equity-based compensation expense				$ 1,274					$ 1,274
Net Income (Loss)							(12,525)		(12,525)
Ending balance at Mar. 31, 2023			$ 2,251	$ 3,416			(52,310)		(46,643)
Ending balance (in shares) at Mar. 31, 2023			5,000,000	1,625,086
Beginning balance at Dec. 31, 2022	$ 28,971	$ 148,496							$ 177,467
Beginning balance (in shares) at Dec. 31, 2022	20,000,000	45,089,212							65,089,212
Ending balance (in shares) at Sep. 30, 2023	20,000,000	45,089,212
Beginning balance at Dec. 31, 2022			$ 2,251	$ 2,142			(39,785)		$ (35,392)
Beginning balance (in shares) at Dec. 31, 2022	20,000,000	45,089,212							65,089,212
Beginning balance (in shares) at Dec. 31, 2022			5,000,000	1,625,086
MEMBERS' DEFICIT
Change in unrealized gains on marketable securities, net of tax									$ 135
Net Income (Loss)									(52,250)
Ending balance at Sep. 30, 2023						$ 501,143	(92,035)	$ 135	409,243
Ending balance (in shares) at Sep. 30, 2023					48,017,621,000
Beginning balance at Mar. 31, 2023	$ 28,971	$ 148,496
Beginning balance (in shares) at Mar. 31, 2023	20,000,000	45,089,212
Ending balance at Jun. 30, 2023	$ 28,971	$ 148,496
Ending balance (in shares) at Jun. 30, 2023	20,000,000	45,089,212
Beginning balance at Mar. 31, 2023			$ 2,251	$ 3,416			(52,310)		(46,643)
Beginning balance (in shares) at Mar. 31, 2023	20,000,000	45,089,212
Beginning balance (in shares) at Mar. 31, 2023			5,000,000	1,625,086
MEMBERS' DEFICIT
Vesting of incentive units				$ 856,457
Equity-based compensation expense				1,113					1,113
Net Income (Loss)							(18,885)		(18,885)
Ending balance at Jun. 30, 2023			$ 2,251	$ 4,529			(71,195)		(64,415)
Ending balance (in shares) at Jun. 30, 2023			5,000,000	2,481,543
Beginning balance (in shares) at Jun. 30, 2023	20,000,000	45,089,212
PREFERRED UNITS
Conversion of preferred, common, and incentive units into common stock	$ (28,971)	$ (148,496)
Conversion of preferred, common, and incentive units into common stock (in shares)	(20,000,000,000)	(45,089,212,000)
Ending balance (in shares) at Sep. 30, 2023	20,000,000	45,089,212
Beginning balance (in shares) at Jun. 30, 2023	20,000,000	45,089,212
MEMBERS' DEFICIT
Vesting of incentive units (in shares)				65,881,000
Conversion of preferred, common, and incentive units into common stock			$ (2,251)	$ (4,686)
Conversion of preferred, common, and incentive units into common stock (in shares)			(5,000,000,000)	(2,547,424,000)	27,597,438,000
Issuance of Common Units in payment of option fee						315,391			315,391
Common stock issued in IPO, net of issuance costs of $29,666						315,391			315,391
Issuance of Common Units in payment of option fee (in shares)					20,297,500,000
Common stock issued in IPO, net of issuance costs of $29,666 (in shares)					20,297,500,000
Vesting of restricted common stock (in shares)					122,683,000
Share-based compensation expense				$ 157		1,348			1,505
Change in unrealized gains on marketable securities, net of tax								135	135
Equity-based compensation expense						184,404			177,467
Net Income (Loss)							(20,840)		(20,840)
Ending balance at Sep. 30, 2023						$ 501,143	$ (92,035)	$ 135	$ 409,243
Ending balance (in shares) at Sep. 30, 2023					48,017,621,000

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENT OF PREFERRED UNITS AND STOCKHOLDERS' EQUITY/MEMBERS' DEFICIT (UNAUDITED) (Parenthetical) $ in Thousands	5 Months Ended
	Jun. 30, 2022 USD ($)
Series A Preferred Units
Net tranche option liability	$ 1,050
Issuance costs	$ 179

CONDENSED CONSOLIDATED STATEM_6

CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	8 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2023
Cash flows from operating activities:
Net loss	$ (25,778)	$ (52,250)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Equity-based compensation expense		3,892
Loss on remeasurement of tranche option liability	9,150
Non-cash research and development license expense	1,688
Amortization of discounts on marketable securities		(232)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets		(3,402)
Accounts payable	36	577
Accrued expenses	7,666	6,408
Net cash used in operating activities	(7,238)	(45,007)
Cash flows from investing activities:
Purchase of marketable securities		(234,218)
Net cash used in investing activities		(234,218)
Cash flows from financing activities:
Proceeds from issuance of Series A Preferred Units and the tranche option, net	9,821
Proceeds from issuance of common stock, net of issuance costs		315,604
Net cash (used in) provided by financing activities	9,821	315,604
Increase (decrease) in cash	2,583	36,379
Cash, beginning of period		151,890
Cash, end of period	2,583	188,269
Supplemental disclosures of non-cash activities:
Exchange of 72,570,755 preferred, common, and incentive units in connection with the Reorganization (Note 1)		184,404
Settlement of Series A Preferred Units tranche obligation	$ 600
Deferred financing issuance costs in accounts payable		$ 213

CONDENSED CONSOLIDATED STATEM_7

CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (UNAUDITED) (Parenthetical) - shares		9 Months Ended
	Jul. 18, 2023	Sep. 30, 2023
CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS (UNAUDITED)
Conversion of preferred, common and incentive units (in shares)	24,987,750	72,570,755

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2023
Nature of the Business
Nature of the Business	1. Apogee Therapeutics, Inc., together with its consolidated subsidiary (collectively, “Apogee” or the “Company”), a successor to Apogee Therapeutics, LLC, is a biotechnology company seeking to develop differentiated biologics for the treatment of atopic dermatitis, asthma, chronic obstructive pulmonary disease and related inflammatory and immunology indications with high unmet need. The Company’s antibody programs are designed to overcome limitations of existing therapies by leveraging clinically validated mechanisms and incorporating advanced antibody engineering to optimize half-life and other properties designed. The Company commenced its operations in February 2022 as a Delaware limited liability company named Apogee Therapeutics, LLC. The Company was founded by leading healthcare investors, Fairmount Funds and Venrock Healthcare Capital Partners and has since assembled a management team of drug developers with significant experience in clinical development. As a result of the Reorganization (as defined below) and in connection with the Company’s initial public offering (“IPO”) in July 2023, the Company directly wholly owns the assets of Apogee Therapeutics, LLC, including the stock of its subsidiary. The Company operates as a virtual company and, thus, does not maintain a corporate headquarters or other significant facilities. In addition, the Company engages third parties, including Paragon Therapeutics, Inc. (“Paragon”), who is also a related party, to perform ongoing research and development and other services on its behalf. In February 2022, the Company entered into an antibody discovery and option agreement with Paragon, which was subsequently amended in November 2022 (as amended, the “2022 Option Agreement”). Under the terms of the 2022 Option Agreement, Paragon identifies, evaluates and develops antibodies directed against certain mutually agreed therapeutic targets of interest to the Company. The 2022 Option Agreement initially included two selected targets, IL-13 and IL-4R α In November 2022, the Company exercised its option available under the 2022 Option Agreement with respect to the IL-13 Research Program (as defined below) and, in April 2023, the Company exercised its options available under the 2022 Option Agreement with respect to the IL-4Rα Research Program and OX40L Research Program. Upon such exercises, the parties entered into associated license agreements for each target. Under the terms of each license agreement, Paragon granted to the Company an exclusive, worldwide, royalty-bearing, sublicensable right and license with respect to certain information, patent rights and sequence information related to antibodies directed at the respective target to use, make, sell, import, export and otherwise exploit the antibodies directed at the respective target. The Company is solely responsible for the development, manufacture and commercialization of IL-13, IL-4Rα and OX40L products at its own cost and expense. On July 13, 2023, the Company completed a reorganization, pursuant to which the members of Apogee Therapeutics, LLC contributed their units in Apogee Therapeutics, LLC to Apogee Therapeutics, Inc. in exchange for shares of common stock or non-voting common stock of Apogee Therapeutics, Inc. and Apogee Therapeutics, LLC became a wholly-owned subsidiary of Apogee Therapeutics, Inc. (the “Reorganization”), as follows: ● holders of Series A Preferred Units of Apogee Therapeutics, LLC received 7,678,000 shares of non-voting common stock of Apogee Therapeutics, Inc.; ● holders of Series B Preferred Units of Apogee Therapeutics, LLC received 11,501,108 shares of common stock and 5,808,642 shares of non-voting common stock of Apogee Therapeutics, Inc.; ● holders of common units of Apogee Therapeutics, LLC received 1,919,500 shares of common stock of Apogee Therapeutics, Inc.; ● holders of vested incentive units of Apogee Therapeutics, LLC received 690,188 shares of common stock of Apogee Therapeutics, Inc.; and ● holders of unvested incentive units of Apogee Therapeutics, LLC received 2,779,358 shares of restricted common stock of Apogee Therapeutics, Inc. On July 18, 2023, the Company completed its IPO, pursuant to which it issued and sold an aggregate of 20,297,500 shares of its common stock (inclusive of 2,647,500 shares pursuant to the exercise of the underwriters’ overallotment option in full) at the IPO price of $17.00 per share for net cash proceeds of $315.4 million, after deducting underwriting discounts and commissions and other offering expenses, including $0.2 million in deferred financing issuance costs in accounts payable as of September 30, 2023. The shares of Apogee Therapeutics, Inc. began trading on the Nasdaq Global Market on July 14, 2023 under the ticker symbol APGE. The Company is subject to risks and uncertainties common to early stage companies in the biotechnology industry, including, but not limited to, completing preclinical studies and clinical trials, obtaining regulatory approval for its programs, market acceptance of products, development by competitors of new technological innovations, dependence on key personnel, the ability to attract and retain qualified employees, reliance on third-party organizations, protection of proprietary technology, compliance with government regulations, and the ability to raise additional capital to fund operations. The Company’s two most advanced programs currently under development, APG777 and APG808, as well as other programs, will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure, and extensive compliance reporting capabilities. Even if the Company’s development efforts are successful, it is uncertain when, if ever, the Company will realize revenue from product sales. The Company has primarily funded its operations with proceeds from the sales of preferred units and common stock and has not generated any revenue since inception. As a result, the Company will need substantial additional funding to support its continued operations and growth strategy. Until such a time as the Company can generate significant revenue from product sales, if ever, the Company expects to finance its operations through the sale of equity, debt financings or other capital sources, including collaborations with other companies or other strategic transactions. The Company may be unable to raise additional funds or enter into such other agreements on favorable terms, or at all. If the Company fails to raise capital or enter into such agreements as, and when, needed, the Company may have to significantly delay, scale back or discontinue the development and commercialization of one or more of its programs. Company Liquidity The Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that the accompanying condensed consolidated financial statements are issued. The Company had an accumulated deficit of $92.0 million as of September 30, 2023. Further, the Company incurred a net loss of $52.3 million and experienced negative cash flows from operations of $45.0 million for the nine months ended September 30, 2023. Based on the Company’s current operating plan, it estimates that its existing cash and cash equivalents of $188.3 million, and marketable securities of $234.6 million as of September 30, 2023 will be sufficient to enable the Company to fund its operating expenses and capital requirements through at least the next twelve months from the issuance of these condensed consolidated financial statements. The Company is subject to those risks associated with any biotechnology company that has substantial expenditures for research and development. There can be no assurance that the Company’s research and development projects will be successful, that products developed will obtain necessary regulatory approval, or that any approved product will be commercially viable. In addition, the Company operates in an environment of rapid technological change and is largely dependent on the services of its employees and consultants. If the Company fails to become profitable or is unable to sustain profitability on a continuing basis, then it may be unable to continue its operations at planned levels and be forced to reduce its operations.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. There have been no material changes to the significant accounting policies as disclosed in Note 2 to the Company’s consolidated financial statements for the period from February 4, 2022 (inception) to December 31, 2022 included in the Company’s final prospectus filed with the Securities and Exchange Commission pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended (the “Securities Act”), on July 17, 2023, except as noted below. Basis of Presentation The condensed consolidated financial statements prior to the Reorganization include the accounts of Apogee Therapeutics, LLC and its wholly-owned subsidiary. The condensed consolidated financial statements subsequent to the Reorganization include the accounts of Apogee Therapeutics, Inc. and its wholly-owned subsidiary. These condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates of the Financial Accounting Standards Board (“FASB”). In the Company’s management opinion, the information furnished in these unaudited condensed consolidated financial statements reflect all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the financial position and results of operations for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. Principles of Consolidation The accompanying condensed consolidated financial statements include the accounts of Apogee Therapeutics, Inc. and its wholly-owned subsidiary, Apogee Biologics, Inc. All intercompany balances and transactions have been eliminated in consolidation. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original final maturities of three months or less from the date of purchase to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in interest-bearing money market funds and U.S. treasury securities. Available-For-Sale Securities The Company’s investments are comprised of U.S. government agency securities and U.S. treasury securities. Investments are classified at the time of purchase, based on management’s intent, as held-to-maturity, available-for-sale, or trading. All of the Company’s marketable security investments are classified as available-for-sale securities and are reported at fair market value using quoted prices in active markets for similar securities. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included as a component of other income within the condensed consolidated statements of operations and comprehensive loss. The Company assesses its available-for-sale securities under the available-for-sale security impairment model in ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Statements as of each reporting date in order to determine if a portion of any decline in fair value below carrying value is the result of a credit loss for its available-for-sale securities. The Company records credit losses for its available-for-sale securities in the condensed consolidated statements of operations and comprehensive loss as credit loss expense, which is limited to the difference between the fair value and the amortized cost of the security. To date, the Company has not recorded any credit losses on its available-for-sale securities. Declines in fair value below carrying value attributable to non-credit related factors are recorded as accumulated other comprehensive loss, which is a separate component of stockholders’ equity. The Company classifies its available-for-sale securities as current assets on the condensed consolidated balance sheets as they mature within one year from the balance sheet date. Equity-Based Compensation Prior to the Reorganization, the Company issued equity-based awards to employees, managers, executives, non-employees and service providers in the form of common units and incentive units. Subsequent to the Reorganization, the Company issued equity-based awards to employees, managers, executives, non-employees and service providers in the form of restricted common stock and stock options. The Company accounts for equity-based compensation awards in accordance with FASB ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). Due to the absence of an active market for the Company’s common units or incentive units prior to the completion of the IPO, the Company utilized methodologies in accordance with the framework of the American Institute of Certified Public Accountants Accounting and Valuation Guide, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common units and incentive units. The estimated fair value of the common units and incentive units was determined at each grant date based upon a variety of factors, including the illiquid nature of the common units, arm’s-length sales of the Company’s equity units (including preferred units), the effect of the rights and preferences of the preferred unit unitholders, and the prospects of a liquidity event. Among other factors are the Company’s financial position and historical financial performance, the status of technological developments within the Company’s research, the composition and ability of the current research and management team, an evaluation or benchmark of the Company’s competition, and the current business climate in the marketplace. Significant changes to the key assumptions underlying the factors used could have resulted in different fair values of the common units and incentive units at each valuation date. Subsequent to the completion of the IPO, the fair value of the Company’s common stock underlying its equity awards is based on the quoted market price of the Company’s common stock on the grant date. The Company estimates the fair value of its stock options using the Black-Scholes option pricing model, which uses as inputs the fair value of the Company’s common stock, and certain management estimates, including the expected stock price volatility, the expected term of the award, the risk-free rate, and expected dividends. Expected volatility is calculated based on reported volatility data for a representative group of publicly traded companies for which historical information is available. The Company selects companies with comparable characteristics with historical share price information that approximates the expected term of the equity-based awards. The Company computes the historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period that approximates the calculated expected term of the stock options. The Company will continue to apply this method until a sufficient amount of historical information regarding the volatility of its stock price becomes available. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant commensurate with the expected term assumption. The Company uses the simplified method, under which the expected term is presumed to be the midpoint between the vesting date and the end of the contractual term. The Company utilizes this method due to lack of historical exercise data. The expected dividend yield is assumed to be zero as the Company has no current plans to pay any dividends on common stock. The Company generally issues equity awards that are subject to either service-based vesting conditions and in limited instances, service-based and performance-based vesting conditions. Compensation expense for awards issued to grantees with service-based vesting conditions are recognized on a straight-line basis based on the grant date fair value over the associated requisite service period of the award, which is generally the vesting term. Compensation expense for awards to grantees with service-based and performance-based vesting conditions are recognized based on the grant-date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable. As of each reporting date, the Company estimates the probability that specified performance criteria will be met and does not recognize compensation expense until it is probable that the performance-based vesting condition will be achieved. The Company evaluates whether an equity award should be classified and accounted for as a liability award or equity award for all equity-based compensation awards granted. As of September 30, 2023, all of the Company’s equity-based awards were equity classified. Forfeitures are recognized as they occur. The Company classifies equity-based compensation expense in the accompanying condensed consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s salary and related costs are classified or in which the award recipient’s service payments are classified, as applicable. Concentrations of Credit Risk and Significant Suppliers Financial instruments that potentially expose the Company to credit risk primarily consist of cash and cash equivalents. The Company maintains its cash and cash equivalents with accredited financial institutions and, consequently, the Company does not believe it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Bank accounts in the United States are insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $250,000. As of September 30, 2023 and December 31, 2022, predominantly all of the Company’s primary operating accounts significantly exceeded the FDIC limits. The Company is dependent on third-party organizations to research, develop, manufacture and process its product candidates for its development programs. In particular, the Company relies on one third-party contract manufacturer to produce and process its two most advanced programs, APG777 and APG808, for preclinical and clinical activities. The Company expects to continue to be dependent on a small number of manufacturers to supply it with its requirements for all products. The Company’s research and development programs could be adversely affected by a significant interruption in the supply of the necessary materials. A significant amount of the Company’s research and development activities are performed under its agreements with Paragon (see Note 7). Off-Balance Sheet Risk As of September 30, 2023 and December 31, 2022, the Company had no off-balance sheet risks such as foreign exchange contracts, option contracts or other foreign hedging arrangements. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders' equity that result from transactions and events other than those with stockholders. The Company’s unrealized gains and losses on available-for-sale securities represent the only component of other comprehensive loss that are excluded from the reported net loss and that are presented in the condensed consolidated statements of comprehensive loss. Net Loss Per Share The Company follows the two-class method when computing net loss per share. Prior to the Reorganization, the Company issued units that met the definition of participating securities, including the Company’s Series A Preferred Units, the Series B Preferred Units, and vested incentive units (each a participating security), and subsequent to the Reorganization, the Company has two classes of common stock outstanding comprised of voting and non-voting shares. The rights of the holders of voting and non-voting shares are identical, except with respect to voting and conversion. Each share of non-voting stock may be converted into one share of voting stock at any time at the option of the stockholder, subject to certain beneficial ownership limitations. The two-class method determines net loss per unit and net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income for the period to be allocated between common and participating securities based upon their respective rights to share in the income as if all income for the period had been distributed. Prior to the Reorganization, during periods of loss, there was no allocation required under the two-class method since the participating securities did not have a contractual obligation to fund the losses of the Company. Subsequent to the Reorganization, net loss per share for each class of common stock issued is the same as they are entitled to the same liquidation and dividend rights. Prior to the Reorganization, the Company calculated basic net loss per common share by dividing net loss by the weighted-average number of common units outstanding for the period. Subsequent to the Reorganization, the Company calculates basic net loss per common share by dividing net loss by the weighted-average number of common shares outstanding for the period. The Company has generated a net loss in the periods presented so the basic and diluted net loss per unit and net loss per share are the same as the inclusion of the potentially dilutive securities would be anti-dilutive. For periods presented that include the Reorganization, including the three and nine months ended September 30, 2023, the weighted-average shares of common stock outstanding include the weighted average number of common units outstanding prior to the Reorganization.

Available-For-Sale Securities

Available-For-Sale Securities	9 Months Ended
	Sep. 30, 2023
Available-For-Sale Securities
Available-For-Sale Securities	3. The Company did not hold any available-for-sale securities as of December 31, 2022. The following is a summary of the Company’s investing portfolio as of September 30, 2023 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ AS OF SEPTEMBER 30, 2023 ​ ​ ​ ​ AMORTIZED ​ UNREALIZED ​ ​ ​ COST GAINS LOSSES FAIR VALUE Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. treasury securities ​ $ 59,685 ​ $ 8 ​ $ — ​ $ 59,693 Marketable securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. treasury securities ​ ​ 117,635 ​ ​ 6 ​ ​ (13) ​ ​ 117,628 Debt securities issued by U.S. government agencies ​ 116,823 ​ 148 ​ (14) ​ 116,957 ​ ​ $ 294,143 ​ $ 162 ​ $ (27) ​ $ 294,278 ​ As of September 30, 2023, the Company had seven securities with a total fair market value of $71.4 million in an unrealized loss position. The Company does not intend to sell its investments before recovery of the amortized cost basis of its debt securities at maturity and no allowance for credit losses was recorded as of September 30, 2023. All securities held by the Company have a maturity date of one year or less. ​ Securities are evaluated at the end of each reporting period. The Company did not record any impairment related to its available-for-sale securities during the three and nine months ended September 30, 2023.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2023
Fair Value Measurements
Fair Value Measurements	4 . The Company estimated the fair value of the Tranche Options, as defined below (see Note 9), at the time of issuance and subsequently remeasured them at each reporting period and prior to settlement, which occurred prior to December 31, 2022. The fair value of the Tranche Options was determined using a contingent forward model, which considered as inputs the estimated fair value of the preferred units as of each valuation date, the risk-free interest rate, probability of achievement, salvage value and estimated time to each tranche closing. The most significant assumptions in the contingent forward model impacting the fair value of the Tranche Options is the fair value of the Company’s Series A Preferred Unit, probability of achievement and time to the tranche closing as of each measurement date. The Company determined the fair value per share of the underlying preferred unit by taking into consideration the most recent sales of its preferred units, results obtained from third-party valuations and additional factors the Company deems relevant. The following table presents information about the Company’s financial assets and liabilities measured at fair value on a reoccurring basis and indicates the level of fair value hierarchy utilized to determine such values as of September 30, 2023 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ AS OF SEPTEMBER 30, 2023 ​ LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 103,776 ​ $ — ​ $ — ​ $ 103,776 U.S. treasury securities ​ ​ 59,693 ​ ​ — ​ ​ — ​ ​ 59,693 Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. treasury securities ​ ​ 117,628 ​ ​ — ​ ​ — ​ ​ 117,628 Debt securities issued by U.S. government agencies ​ — ​ 116,957 ​ — ​ 116,957 ​ ​ $ 281,097 ​ $ 116,957 ​ $ — ​ $ 398,054 ​ The following table provides a reconciliation of all assets and liabilities measured at fair value using Level 3 significant unobservable inputs which were settled during the period from February 4, 2022 (inception) to September 30, 2022 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PREFERRED UNIT PREFERRED UNIT PREFERRED UNIT ​ ​ TRANCHE OPTION ​ TRANCHE OPTION ​ TRANCHE OPTION, ​ ASSET (LIABILITY) NET Balance as of February 4, 2022 (inception) ​ $ — ​ $ — ​ $ — Issuance ​ 650 ​ (1,700) ​ (1,050) Change in fair value ​ ​ (50) ​ ​ (9,100) ​ ​ (9,150) Transfer to temporary equity upon settlement ​ (600) ​ — ​ (600) Balance as of September 30, 2022 ​ $ — ​ $ (10,800) ​ $ (10,800) ​

Prepaids and Other Current Asse

Prepaids and Other Current Assets	9 Months Ended
	Sep. 30, 2023
Prepaids and Other Current Assets
Prepaids and Other Current Assets	5. Prepaids and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ SEPTEMBER 30, DECEMBER 31, ​ ​ 2023 ​ 2022 Prepaid expenses ​ $ 2,156 ​ $ 108 Other current assets ​ 1,411 ​ 57 Total ​ $ 3,567 ​ $ 165 ​

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2023
Accrued Expenses
Accrued Expenses	6. Accrued Expenses Accrued expenses consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ SEPTEMBER 30, DECEMBER 31, ​ ​ 2023 ​ 2022 Accrued external research and development expenses ​ $ 13,057 ​ $ 8,847 Accrued other ​ 692 ​ 200 Accrued employee compensation ​ 2,221 ​ 515 Total ​ $ 15,970 ​ $ 9,562 ​

Other Significant Agreements Pa

Other Significant Agreements Paragon Option Agreement	9 Months Ended
	Sep. 30, 2023
Other Significant Agreements Paragon Option Agreement
Other Significant Agreements Paragon Option Agreement	7 . Paragon Option Agreements In February 2022, the Company entered into an antibody discovery and option agreement with Paragon, which was subsequently amended in November 2022 (as amended, the “2022 Option Agreement”). Under the terms of the 2022 Option Agreement, Paragon identifies, evaluates and develops antibodies directed against certain mutually agreed therapeutic targets of interest to the Company. The 2022 Option Agreement initially included two selected targets, IL-13 and IL-4R α Pursuant to the terms of the 2022 Option Agreement, the parties initiated certain research programs that generally focus on a particular target (each, a “Research Program”). Each Research Program is aimed at discovering, generating, identifying and/or characterizing antibodies directed to the respective target. For each Research Program, the parties established a research plan that sets forth the activities that will be conducted, and the associated research budget (each, a “Research Plan”). Upon execution of the 2022 Option Agreement, the Company and Paragon agreed on an initial Research Plan that outlined the services that will be performed commencing at inception of the arrangement related to IL-13 and IL-4R α of days following the delivery of the data package from Paragon related to the results of the Research Plan activities (the “Option Period”). There is no payment due upon exercise of an Option pursuant to the 2022 Option Agreement. Unless terminated earlier, the 2022 Option Agreement shall continue in force on a Research Program-by-Research Program basis until the earlier of: (i) the end of the Option Period for such Research Program, as applicable, if such Option is not exercised by the Company; and (ii) the effective date of the license agreement for such Research Program if the Company exercises its Option with respect to such Research Program (the “2022 Term”). Upon the expiration of the 2022 Term for all then-existing Research Programs, under the 2022 Option Agreement, the 2022 Option Agreement will automatically expire in its entirety. The Company may terminate the 2022 Option Agreement or any Research Program at any time for any or no reason upon 30 days 30 days In consideration for the exclusive options granted under the 2022 Option Agreement, the Company paid an upfront cash amount of $1.3 million and issued 1,250,000 common units to Paragon. Paragon was also entitled to up to an additional 3,750,000 of common units in exchange for the rights granted under the 2022 Option Agreement, which were issued in connection with the closings of the additional Tranche Options of the Series A Preferred Unit financing (see Note 9). Through December 31, 2022, the Company had issued a total of 5,000,000 common units to Paragon with an aggregate fair value of $2.2 million on the grant date. Under the 2022 Option Agreement, on a Research Program-by-Research Program basis following the finalization of the Research Plan for each respective Research Program, the Company is required to pay Paragon a nonrefundable fee in cash of $0.5 million. The Company is also obligated to compensate Paragon on a quarterly basis for its services performed under each Research Program based on the actual costs incurred. The Company expenses the service fees as the associated costs are incurred when the underlying services are rendered. Such amounts are classified within research and development expenses in the accompanying condensed consolidated statement of operations and comprehensive loss. The Company concluded that the rights obtained under the 2022 Option Agreement represent an asset acquisition whereby the underlying assets comprise in-process research and development assets with no alternative future use. The 2022 Option Agreement did not qualify as a business combination because substantially all of the fair value of the assets acquired was concentrated in the exclusive license options, which represent a group of similar identifiable assets. Therefore, the aggregate acquisition cost of $2.9 million, related to the upfront cash and equity payments, was recognized as acquired in-process research and development expense, which is reported as a component of research and development expense during the period from February 4, 2022 (inception) to September 30, 2022. Amounts paid as on-going development cost reimbursements associated with services being rendered under the related Research Programs is recognized as research and development expense when incurred. In November 2023, the Company entered into an additional antibody discovery and option agreement with Paragon (the “2023 Option Agreement,” and together with the 2022 Option Agreement, collectively the “Option Agreements”). Under the terms of the 2023 Option Agreement, Paragon identifies, evaluates and develops antibodies directed against certain mutually agreed therapeutic targets of interest to the Company. The 2023 Option Agreement initially includes one undisclosed target. Under the 2023 Option Agreement, the Company has the exclusive option to, on a research program-by-research program basis, be granted an exclusive, worldwide license to all of Paragon’s right, title and interest in and to the intellectual property resulting from the applicable research program to develop, manufacture and commercialize the antibodies and products directed to the selected targets Option. From time to time, the Company can choose to add additional targets to the collaboration by mutual agreement with Paragon. Pursuant to the terms of the 2023 Option Agreement, the parties may initiate Research Programs. Each Research Program is aimed at discovering, generating, identifying and/or characterizing antibodies directed to the respective target. For each Research Program, the parties must establish a Research Plan. The Company and Paragon will agree on an initial Research Plan that outlines the services that will be performed commencing at inception of the arrangement related to the undisclosed target. The Company’s exclusive option with respect to each Research Program is exercisable at its sole discretion at any time during the period beginning on the initiation of activities under the associated Research Program and ending a specified number of days following the delivery of the data package from Paragon related to the results of the Research Plan activities. There is no payment due upon exercise of an Option pursuant to the 2023 Option Agreement. Following entry into the 2023 Option Agreement, the Company and Paragon will negotiate a form of License Agreement to be entered into in the event that the Company exercises its exclusive option with respect to each Research Program, which License Agreement will include certain pre-agreed economic and other business terms. Unless terminated earlier, the 2023 Option Agreement shall continue in force on a Research Program-by-Research Program basis until the earlier of: (i) the end of the Option Period for such Research Program, as applicable, if such Option is not exercised by the Company; and (ii) the effective date of the license agreement for such Research Program if the Company exercises its Option with respect to such Research Program (the “2023 Term”). Upon the expiration of the 2023 Term for all then-existing Research Programs, under the 2023 Option Agreement, the 2023 Option Agreement will automatically expire in its entirety. The Company may terminate the 2023 Option Agreement or any Research Program at any time for any or no reason upon 30 days’ prior written notice to Paragon, provided that the Company must pay certain unpaid fees due to Paragon upon such termination, as well as any non-cancellable obligations reasonably incurred by Paragon in connection with its activities under any terminated Research Program. Each party has the right to terminate the 2023 Option Agreement or any Research Program upon (i) 30 days’ prior written notice of the other party’s material breach that remains uncured for the 30 day period and (ii) the other party’s bankruptcy. Under the 223 Option Agreement, on a Research Program-by-Research Program basis following the finalization of the Research Plan for each respective Research Program, the Company is required to pay Paragon a nonrefundable fee in cash of $2.0 million. The Company is also obligated to compensate Paragon on a quarterly basis for its services performed under each Research Program based on the actual costs incurred. The Company expenses the service fees as the associated costs are incurred when the underlying services are rendered. For the three months ended September 30, 2022 and for the period from February 4, 2022 (inception) to September 30, 2022, the Company recognized $9.6 million and $15.5 million, respectively, and for the three and nine months ended September 30, 2023, the Company recognized $4.4 million and $12.1 million, respectively, of research and development expense in connection with services provided by Paragon under the Option Agreements, including nonrefundable fees following the finalization of a Research Plan. Paragon License Agreements In November 2022, the Company exercised its option available under the 2022 Option Agreement with respect to the IL-13 Research Program. Upon such exercise, the parties entered into an associated license agreement (the “IL-13 License Agreement”). In April 2023, the Company exercised its option available under the 2022 Option Agreement with respect to the IL- 4Rα Research Program and OX40L Research Program. Upon such exercise, the parties entered into associated license agreements (the “IL-4Rα License Agreement” and the “OX40L License Agreement,” respectively, and collectively with the IL-13 License Agreement, the “License Agreements”). Under the terms of each of the License Agreements, Paragon granted to the Company an exclusive, worldwide, royalty-bearing, sublicensable right and license with respect to certain information, patent rights and sequence information related to antibodies directed at the respective target to use, make, sell, import, export and otherwise exploit the antibodies directed at the respective target. Pursuant to the License Agreements, the Company granted to Paragon a similar license (except that such license the Company granted to Paragon is non-exclusive) to the respective licenses with respect to multispecific antibodies that are directed at the respective target and one or more other antibodies. The Company was also granted a right of first negotiation with Paragon concerning the development, license and grant of rights to certain multispecific antibodies associated with each license. The Company is solely responsible for the continued development, manufacture and commercialization of products at its own cost and expense for each licensed target. The Company is obligated to pay Paragon up to $3.0 million upon the achievement of specific development and clinical milestones for the first product under each of the License Agreements that achieves such specified milestones, including a payment of $1.0 million upon the nomination of a development candidate and $2.0 million upon the first dosing of a human patient in a Phase 1 trial. Upon execution of the IL-13 License Agreement, the Company paid Paragon a $1.0 million fee for the nomination of a development candidate. In August 2023, the Company dosed its first participant in the Phase 1 trial of APG777 and incurred a milestone payment of $2.0 million to Paragon in the third quarter of 2023. The nomination of a development candidate under the IL-4Rα License Agreement and the OX40L License Agreement had not yet occurred as of September 30, 2023. Except for the two milestone payments totaling an aggregate of $3.0 million, no other milestone or royalty payments have become due to Paragon through September 30, 2023. In November 2023, the Company finalized the nomination of a development candidate under the IL-4Rα License Agreement and will make a milestone payment of $1.0 million to Paragon in the fourth quarter of 2023. The Company is also obligated to pay royalties to Paragon equal to a low-single digit percentage of net sales of any products under each of the License Agreements, and Paragon has a similar obligation to pay royalties to the Company with respect to the each of the multispecific licenses. Royalties are due on a product-by-product and country-by-country basis beginning upon the first commercial sale of each product and ending on the later of (i) 12 years after the first commercial sale of such product in such country and (ii) expiration of the last valid claim of a patent covering such product in such country (the “Royalty Term”). Unless earlier terminated, the License Agreements remain in effect until the expiration of the last-to-expire Royalty Term for any and all Products associated with the respective license. The Company may terminate the agreement in its entirety or on a country-by-country or product-by-product at any time for any or no reason upon 60 days’ advance written notice to Paragon, and either party may terminate for (i) the other party’s material breach that remains uncured for 90 days (or 30 days with respect to any failure to make payments) following notice of such breach and (ii) the other party’s bankruptcy. Upon any termination prior to the expiration of a License Agreement, all licenses and rights granted pursuant to such License Agreement will automatically terminate and revert to the granting party and all other rights and obligations of the parties will terminate. The Company concluded that each of the License Agreements constitutes an asset acquisition of in-process research and development assets with no alternative future use. Each of the arrangements did not qualify as a business combination because substantially all of the fair value of the assets acquired was concentrated in the license which comprises a single identifiable asset. Therefore, the aggregate acquisition cost for each license was recognized as research and development expense. No expense was recognized for the three months ended September 30, 2022 and for the period from February 4, 2022 (inception) to September 30, 2022, as a program candidate was not nominated until November 2022. For the three and nine months ended September 30, 2023, the Company recognized $2.3 million and $9.1 million, respectively, of research and development expense in connection with services provided by Paragon under the License Agreements. Biologics Master Services Agreement — WuXi Biologics (Hong Kong) Limited In June 2022, Paragon and WuXi Biologics (Hong Kong) Limited (“WuXi Biologics”) entered into a biologics master services agreement (the “WuXi Biologics MSA”), which was subsequently novated to the Company by Paragon in the second quarter of 2023. The WuXi Biologics MSA governs all development activities and GMP manufacturing and testing for APG777 and APG808 programs, as well as the Company’s other programs, on a work order basis. Under the WuXi Biologics MSA, the Company is obligated to pay WuXi Biologics a service fee and all non-cancellable obligations in the amount specified in each work order associated with the agreement for the provision of services. The WuXi Biologics MSA terminates on the later of (i) June 20, 2027 or (ii) the completion of services under all work orders executed by the parties prior to June 20, 2027, unless terminated earlier. The term of each work order terminates upon completion of the services under such work order, unless terminated earlier. The Company can terminate the WuXi Biologics MSA or any work order at any time upon 30 days’ prior written notice and immediately upon written notice if WuXi Biologics fails to obtain or maintain required material governmental licenses or approvals. Either party may terminate a work order (i) at any time upon six months’ prior notice with reasonable cause, provided however that if WuXi Biologics terminates a work order in such manner, no termination or cancellation fees shall be paid busy the Company and (ii) immediately for cause upon (a) the other party’s material breach that remains uncured for 30 days after notice of such breach, (b) the other party’s bankruptcy or (c) a force majeure event that prevents performance for a period of at least 90 days. For the three and nine months ended September 30, 2023, the Company recognized $6.4 million and $9.6 million, respectively, of research and development expense in connection with the WuXi Biologics MSA subsequent to novation. As of September 30, 2023, there were no non-cancelable obligations under the WuXi Biologics MSA. Cell Line License Agreement — WuXi Biologics (Hong Kong) Limited In June 2022, Paragon and WuXi Biologics entered into a cell line license agreement (the “Cell Line License Agreement”), which was subsequently novated to the Company by Paragon in the second quarter of 2023. Under the Cell Line License Agreement, the Company received a non-exclusive, worldwide, sublicensable license to certain of WuXi Biologics’s know-how, cell line, biological materials (the “WuXi Biologics Licensed Technology”) and media and feeds to make, have made, use, sell and import certain therapeutic products produced through the use of the cell line licensed by WuXi Biologics under the Cell Line License Agreement (the “WuXi Biologics Licensed Products”). Specifically, the WuXi Biologics Licensed Technology is used to manufacture a component of the APG777 and APG808 programs. In consideration for the license, the Company agreed to pay WuXi Biologics a non-refundable license fee of $150,000 for each licensed cell line. Additionally, if the Company manufactures all of its commercial supplies of bulk drug product with a manufacturer other than WuXi Biologics or its affiliates, it is required to make royalty payments to WuXi Biologics in an amount equal to a fraction of a single digit percentage of global net sales of WuXi Biologics Licensed Products manufactured by a third-party manufacturer (the “Royalty”). If the Company manufactures part of its commercial supplies of the WuXi Biologics Licensed Products with WuXi Biologics or its affiliates, then the Royalty will be reduced accordingly on a pro rata basis. The Cell Line License Agreement will continue indefinitely unless terminated (i) by the Company upon six months’ prior written notice and its payment of all undisputed amounts due to WuXi Biologics through the effective date of termination, (ii) by WuXi Biologics for a material breach by the Company that remains uncured for 60 days after written notice, (iii) by WuXi Biologics if the Company fails to make a payment and such failure continues for 30 days after receiving notice of such failure, or (iv) by either party upon the other party’s bankruptcy.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies
Commitments and Contingencies	8 . Other Contracts Currently, all of the Company’s preclinical and clinical drug manufacturing, storage, distribution or quality testing are outsourced to third-party manufacturers. As development programs progress and new process efficiencies are built, the Company expects to continually evaluate this strategy with the objective of satisfying demand for registration trials and, if approved, the manufacture, sale and distribution of commercial products. Under such agreements, the Company is contractually obligated to make certain payments to vendors upon early termination, primarily to reimburse them for their unrecoverable outlays incurred prior to cancellation as well as any amounts owed by the Company prior to early termination. The actual amounts the Company could pay in the future to the vendors under such agreements may differ from the purchase order amounts due to cancellation provisions. Indemnification Agreements The Company enters into standard indemnification agreements and/or indemnification sections in other agreements in the ordinary course of business. Pursuant to the agreements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements. The Company was not aware of any claims under these indemnification arrangements as of September 30, 2023 and December 31, 2022. Legal Proceedings The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of FASB ASC Topic 450, Contingencies ( “ ” )

Preferred Units

Preferred Units	9 Months Ended
	Sep. 30, 2023
Preferred Units
Preferred Units	9. As of December 31, 2022, the Company had authorized, issued outstanding Series A Preferred Units On February 24, 2022, the Company executed the Series A Preferred Unit Purchase Agreement (the “Series A Agreement”) to issue and sell up to 20,000,000 Series A Preferred Units at a purchase price of $1.00 per unit. In the initial closing on February 24, 2022, the Company issued 5,000,000 Series A Preferred Units at a purchase price of $1.00, resulting in gross cash proceeds to the Company of $5.0 million, and incurred $0.2 million of issuance costs. The Series A Agreement provided for three tranche option closings following the initial closing (the “Tranche Options”), which Tranche Option closings were subject to approval of the Board of Managers of Apogee Therapeutics, LLC (the “Board of Managers”), which was controlled by the holders of the Series A Preferred Units. The Board of Managers approved all such subsequent closings resulting in investors purchasing 5,000,000 Series A Preferred Units in each of the three subsequent Tranche Option closings throughout 2022. As a result, the Company received an aggregate of $20.0 million in gross proceeds associated with the Series A Agreement. The Company assessed the Tranche Options and concluded that they met the definition of a freestanding financial instrument, as the Tranche Options were legally detachable and separately exercisable from the Series A Preferred Units. Therefore, the Company allocated the proceeds between the Tranche Options and the Series A Preferred Units sold at the initial closing. As the Series A Preferred Units are contingently redeemable upon an event that is not completely within the control of the Company, the Tranche Options are classified as an asset or liability and are initially recorded at fair value. The Tranche Options are measured at fair value at each reporting period, through the settlement of the instrument. Since the Tranche Options are subject to fair value accounting, the Company allocated $1.1 million of the initial proceeds to the Tranche Options based on the fair value at the date of issuance with the remaining proceeds beings allocated to the Series A Preferred Units. Upon the Tranche Option closings in August and October 2022, the respective Tranche Option value was remeasured at fair value and then reclassified to Series A Preferred Units upon settlement. Series B Preferred Units On November 15, 2022, the Company executed the Series B Preferred Unit Purchase Agreement (the “Series B Agreement”) to issue and sell 45,089,212 Series B Preferred Units in a single closing at a purchase price of $3.30456 per unit, resulting in gross cash proceeds to the Company of $149.0 million. The Company incurred $0.5 million of issuance costs in connection with the issuance of the Series B Preferred Units. The Company’s preferred units as of December 31, 2022 consisted of the following (in thousands, except unit amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PREFERRED ​ ​ ​ ​ ​ ​ PREFERRED ​ UNITS ​ ​ ​ ​ ​ ​ ​ ​ UNITS ​ ISSUED AND ​ CARRYING ​ LIQUIDATION ​ ​ AUTHORIZED ​ OUTSTANDING ​ VALUE ​ PREFERENCE Series A Preferred Units 20,000,000 20,000,000 ​ $ 28,971 ​ $ 20,000 Series B Preferred Units 45,089,212 45,089,212 ​ 148,496 ​ 149,000 Total 65,089,212 65,089,212 ​ $ 177,467 ​ $ 169,000 ​ Embedded Securities Evaluation The Company assessed the Series A Preferred Units and the Series B Preferred Units for any features that may require separate accounting under FASB ASC Topic 815- Derivatives and Hedging

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2023
Common Stock.
Common Stock	10. In July 2023, the Company completed its IPO, selling an aggregate 20,297,500 shares of common stock. All outstanding preferred units were exchanged into 24,987,750 shares of common stock in connection with the IPO. Following the IPO, the Company is authorized to issue 400,000,000 shares of common stock, par value $0.00001. As of September 30, 2023, 50,674,296 and 48,017,621 shares of common stock were issued and outstanding, respectively. The 50,674,296 shares of common stock issued is comprised of 37,187,654 shares of voting common stock, and 13,486,642 shares of non-voting common stock, respectively. As of September 30, 2023, there are 2,656,675 shares of unvested restricted common stock included within the shares of common stock issued. ​ As of December 31, 2022, the Company had 5,000,000 common units authorized, issued outstanding

Equity-Based Compensation

Equity-Based Compensation	9 Months Ended
	Sep. 30, 2023
Equity-Based Compensation
Equity-Based Compensation	11 . Incentive Units Prior to the Reorganization, the Company periodically granted incentive units to employees, managers and executives, as well as to consultants and service providers of the Company. The incentive units represent a separate substantive class of members’ equity with defined rights. The incentive units represent profits interest in the increase in the value of the entity over a threshold value, or strike price, as determined at the time of grant. The strike price is established for tax compliance purposes related to Internal Revenue Service Revenue Procedure 93-27 and 2001-43 where the Company allocates equity value to separate classes of equity in a hypothetical liquidation transaction as of the date of grant. Each incentive unit issued includes a strike price determined by the Board of Managers. The strike price is based on an estimate of the amount a common unit would receive on the date of issuance of such incentive units in a hypothetical liquidation of the Company in which the Company sold its assets for their fair market value, satisfied its liabilities, and distributed the net proceeds to the holders of units in liquidation of the Company. The Company accounts for equity-based compensation in accordance with ASC 718. In accordance with ASC 718, compensation cost is measured at estimated fair value and is included as compensation expense over the vesting period during which service is provided in exchange for the award. The service-based incentive unit grants generally vest over a four-year service period, with the first 25% vesting on the 12-month anniversary of the vesting start date and the remaining vesting in equal monthly installments over The Company determined that incentive units issued to employees, managers, executives, non-employees and service providers are equity-based service payments and, as such, the Company measures and recognizes the related compensation expense in a manner consistent with its accounting policy for equity-based awards. The fair value of each incentive unit grant is estimated on the grant date using either an option pricing method (“OPM”), or a hybrid method, both of which use market approaches to estimate the Company’s enterprise value. The OPM treats common units, incentive units and preferred units as call options on the total equity value of a company, with exercise prices based on the value thresholds at which the allocation among the various holders of a company’s securities changes. Under this method, the incentive units have value only if the funds available for distribution to unitholders exceed the value of the preferred and common unit distribution preferences and the strike price with respect to such incentive unit at the time of the liquidity event. The hybrid method is a probability-weighted expected return method (“PWERM”), where the equity value is allocated in one or more of the scenarios using an OPM. The PWERM is a scenario-based methodology that estimates the fair value of each unit based upon an analysis of future values, assuming various outcomes. The incentive unit value is based on the probability-weighted value across the scenarios, considering the OPM to estimate the value within each scenario given the rights of each class of unit. A discount for lack of marketability of the incentive unit is then applied to arrive at an indication of fair value for the incentive unit. The following assumptions were used in determining the fair value of incentive units granted during the period: ​ ​ ​ ​ ​ ​ NINE MONTHS ​ ​ ENDED ​ ​ ​ SEPTEMBER 30, ​ ​ ​ 2023 ​ Risk free interest rate ​ 4.1% - 4.9% Expected dividend yield ​ 0.0% Expected term (in years) ​ 0.17 – 2 Expected volatility ​ 84% - 90% ​ The following table summarizes the Company’s unvested incentive unit activity: ​ ​ ​ ​ ​ ​ ​ ​ ​ WEIGHTED- ​ ​ ​ ​ AVERAGE ​ ​ NUMBER OF ​ GRANT DATE FAIR ​ ​ UNITS ​ VALUE PER UNIT Unvested incentive units as of December 31, 2022 8,023,288 ​ $ 1.20 Granted ​ 4,621,901 ​ $ 1.32 Vested ​ (922,338) ​ $ 1.54 Exchanged for unvested restricted common stock (11,722,851) ​ $ 1.22 Unvested incentive units as of September 30, 2023 — ​ $ — ​ Restricted Common Stock Concurrent with the Reorganization, all of the outstanding incentive units were exchanged into 3,469,546 shares of common stock, of which 2,779,358 were unvested restricted common stock. The following table provides a summary of the unvested restricted common stock award activity during the nine months ended September 30, 2023: ​ ​ ​ ​ ​ ​ ​ ​ ​ WEIGHTED- ​ ​ ​ ​ AVERAGE ​ ​ NUMBER OF ​ GRANT DATE FAIR ​ ​ SHARES ​ VALUE PER SHARE Unvested restricted common stock as of December 31, 2022 — ​ $ — Exchange of incentive units ​ 2,779,358 ​ $ 5.16 Vested (122,683) ​ $ 3.78 Unvested restricted common stock as of September 30, 2023 2,656,675 ​ $ 5.22 ​ 2023 Equity Incentive Plan In July 2023, in connection with the IPO, the Company’s Board of Directors (the “Board”) and stockholders approved the 2023 Equity Incentive Plan (the “2023 Plan”), which became effective on the date of the effectiveness of the registration statement for the IPO. The 2023 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, awards of restricted stock, restricted stock units and other stock-based awards. The number of shares of common stock reserved for issuance under the 2023 Plan is equal to 6,706,037 shares of common stock. The number of shares available for grant and issuance under the 2023 Plan will be automatically increased on January 1 of each year by a number of shares equal to up to 5% of the outstanding shares of common stock on such date. The Company uses the Black-Scholes option pricing model to estimate the fair value of stock options granted with the following assumptions: ​ ​ ​ ​ ​ ​ THREE MONTHS ​ ​ ENDED ​ ​ SEPTEMBER 30, ​ 2023 Common stock fair value ​ $17.00 - $23.60 Risk free interest rate ​ 1.8% - 2.1% Expected dividend yield ​ 0.0% Expected term (in years) ​ 5.75 - 6.25 Expected volatility ​ 96.8% - 99.9% ​ The following table provides a summary of stock option activity under the 2023 Plan during the nine months ended September 30, 2023: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ WEIGHTED- ​ WEIGHTED- ​ AGGREGATE ​ ​ ​ ​ AVERAGE ​ AVERAGE ​ INTRINSIC ​ ​ ​ ​ EXERCISE ​ REMAINING ​ VALUE ​ ​ OPTIONS ​ PRICE CONTRACTUAL TERM (IN THOUSANDS) Outstanding as of December 31, 2022 — ​ $ — ​ ​ — ​ $ — Granted ​ 637,546 ​ $ 20.28 ​ ​ 9.84 ​ $ — Outstanding as of September 30, 2023 ​ 637,546 ​ $ 20.28 ​ ​ 9.84 ​ $ 1,317 Vested and expected to vest as of September 30, 2023 637,546 ​ $ 20.28 ​ ​ 9.84 ​ $ 1,317 Exerciseable as of September 30, 2023 1,389 ​ $ 23.60 ​ ​ 9.89 ​ $ — ​ 2023 Employee Stock Purchase Plan In July 2023, the Board adopted and the Company’s stockholders approved the 2023 Employee Stock Purchase Plan, (the “ESPP”), which became effective on July 13, 2023. A total of 479,003 shares of common stock were reserved for issuance under the ESPP. As of September 30, 2023, no shares have been issued under the ESPP. Equity-Based Compensation Expense The following table presents the classification of equity-based compensation expense related to equity awards granted to employees, managers, executives, and service providers (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ THREE MONTHS NINE MONTHS FEBRUARY 4, 2022 ​ ​ ENDED SEPTEMBER 30, ​ ENDED SEPTEMBER 30, ​ (INCEPTION) to ​ ​ ​ 2023 ​ 2023 ​ SEPTEMBER 30, 2022 ​ Research and development expense ​ $ 417 ​ $ 755 ​ $ — ​ General and administrative expense ​ 1,088 ​ 3,137 ​ — ​ Total ​ $ 1,505 ​ $ 3,892 ​ $ — ​ ​ As of September 30, 2023, the total unrecognized compensation expense related to the Company’s unvested restricted stock and stock options was $21.4 million, which the Company expects to recognize over a weighted-average period of approximately 3.0 years. For the period from February 4, 2022 (inception) to September 30, 2022, the Company recognized an additional $1.7 million of equity-based compensation expense, in connection with the additional common units issued under the 2022 Option Agreement with Paragon. ​ In August 2023, the Board approved two option grants to the new Chairman of the Board, (1) to purchase 50,000 shares of the Company’s common stock under the 2023 Plan (“first option”), and (2) to purchase 100,000 shares of the Company’s common stock outside of the 2023 Plan (“second option”), in which the shares underlying both options will vest and become exercisable in equal monthly installments over a three-year period from August 2023. The second option is contingent upon approval of the shares underlying the award by the Company’s stockholders at the 2024 Annual Meeting of Stockholders and failure to obtain stockholder approval will result in the forfeiture of the award. Prior to receiving stockholder approval for the second option, neither a grant date nor a service inception date will occur, and no compensation cost is recognized for the award. Should stockholder approval be received at the 2024 Annual Meeting of Stockholders, a cumulative catch-up in equity-based compensation for the second option will be recognized on the date of stockholder approval .

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 2023
Related Parties
Related Parties	12. Related Parties Under the Option Agreements and the License Agreements, Paragon, a member of the Company which was founded by a Series A Unit investor, received upfront consideration in the form of common units, is entitled to receive milestone and royalty payments upon specific conditions and receives payments from the Company for providing ongoing services under the agreements (see Note 7). As of September 30, 2023 and December 31, 2022, $6.6 million and $8.0 million was due to Paragon, respectively. The Company incurred $6.6 million and $21.1 million of research and development expenses for the three and nine months ended September 30, 2023, respectively. The Company incurred $9.6 million and $15.2 million of research and development expenses for the three months ended September 30, 2022 and for the period from February 4, 2022 (inception) to September 30, 2022, respectively.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2023
Net Loss Per Share
Net Loss Per Share	13. Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PERIOD FROM ​ ​ ​ ​ ​ ​ ​ ​ NINE MONTHS FEBRUARY 4 ​ ​ ​ THREE MONTHS ENDED SEPTEMBER 30, ​ ENDED SEPTEMBER 30, ​ (INCEPTION) TO ​ ​ 2023 2022 2023 SEPTEMBER 30, 2022 Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss ​ $ (20,840) ​ $ (19,657) ​ $ (52,250) ​ $ (25,778) ​ Net loss attributable to common stockholders, basic and diluted ​ $ (20,840) ​ $ (19,657) ​ $ (52,250) ​ $ (25,778) ​ Denominator: ​ ​ ​ ​ ​ ​ ​ Weighted average shares of common stock outstanding, basic and diluted ​ ​ 41,231,379 ​ ​ 2,078,804 ​ ​ 17,209,842 ​ ​ 1,516,736 ​ Net loss per share attributable to common stockholders, basic and diluted ​ $ (0.51) ​ $ (9.46) ​ $ (3.04) ​ $ (17.00) ​ ​ The following potential common shares, presented based on amounts outstanding period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the period indicated because including them would have been anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PERIOD FROM ​ ​ ​ ​ ​ ​ NINE MONTHS FEBRUARY 4 ​ ​ ​ THREE MONTHS ENDED SEPTEMBER 30, ​ ENDED ​ (INCEPTION) TO ​ ​ 2023 2022 SEPTEMBER 30, 2023 SEPTEMBER 30, 2022 Series A Preferred Units — ​ 10,000,000 ​ — 10,000,000 ​ Stock options ​ 637,546 ​ — ​ 637,546 ​ — ​ Unvested restricted common stock 2,656,675 ​ — ​ 2,656,675 — ​ Total 3,294,221 ​ 10,000,000 ​ 3,294,221 10,000,000 ​ ​

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2023
Subsequent Events
Subsequent Events	14. The Company evaluated subsequent events through the date on which these financial statements were issued to ensure that these condensed consolidated financial statements include appropriate disclosure of events both recognized in the financial statements as of September 30, 2023 and events which occurred subsequently but not recognized in the financial statements. No subsequent events have occurred that require disclosure, except as disclosed below. ​ In November 2023, the Company finalized the nomination of a development candidate under the IL-4Rα License Agreement and will make a milestone payment of $1.0 million to Paragon in the fourth quarter of 2023. ​ In November 2023, the Company entered into the 2023 Option Agreement with Paragon. Under the terms of the 2023 Option Agreement, Paragon identifies, evaluates and develops antibodies directed against certain mutually agreed therapeutic targets of interest to the Company.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The condensed consolidated financial statements prior to the Reorganization include the accounts of Apogee Therapeutics, LLC and its wholly-owned subsidiary. The condensed consolidated financial statements subsequent to the Reorganization include the accounts of Apogee Therapeutics, Inc. and its wholly-owned subsidiary. These condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates of the Financial Accounting Standards Board (“FASB”). In the Company’s management opinion, the information furnished in these unaudited condensed consolidated financial statements reflect all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the financial position and results of operations for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period.
Principles of Consolidation	Principles of Consolidation The accompanying condensed consolidated financial statements include the accounts of Apogee Therapeutics, Inc. and its wholly-owned subsidiary, Apogee Biologics, Inc. All intercompany balances and transactions have been eliminated in consolidation.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original final maturities of three months or less from the date of purchase to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in interest-bearing money market funds and U.S. treasury securities.
Available-For-Sale Securities	Available-For-Sale Securities The Company’s investments are comprised of U.S. government agency securities and U.S. treasury securities. Investments are classified at the time of purchase, based on management’s intent, as held-to-maturity, available-for-sale, or trading. All of the Company’s marketable security investments are classified as available-for-sale securities and are reported at fair market value using quoted prices in active markets for similar securities. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included as a component of other income within the condensed consolidated statements of operations and comprehensive loss. The Company assesses its available-for-sale securities under the available-for-sale security impairment model in ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Statements as of each reporting date in order to determine if a portion of any decline in fair value below carrying value is the result of a credit loss for its available-for-sale securities. The Company records credit losses for its available-for-sale securities in the condensed consolidated statements of operations and comprehensive loss as credit loss expense, which is limited to the difference between the fair value and the amortized cost of the security. To date, the Company has not recorded any credit losses on its available-for-sale securities. Declines in fair value below carrying value attributable to non-credit related factors are recorded as accumulated other comprehensive loss, which is a separate component of stockholders’ equity. The Company classifies its available-for-sale securities as current assets on the condensed consolidated balance sheets as they mature within one year from the balance sheet date.
Equity-Based Compensation	Equity-Based Compensation Prior to the Reorganization, the Company issued equity-based awards to employees, managers, executives, non-employees and service providers in the form of common units and incentive units. Subsequent to the Reorganization, the Company issued equity-based awards to employees, managers, executives, non-employees and service providers in the form of restricted common stock and stock options. The Company accounts for equity-based compensation awards in accordance with FASB ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). Due to the absence of an active market for the Company’s common units or incentive units prior to the completion of the IPO, the Company utilized methodologies in accordance with the framework of the American Institute of Certified Public Accountants Accounting and Valuation Guide, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common units and incentive units. The estimated fair value of the common units and incentive units was determined at each grant date based upon a variety of factors, including the illiquid nature of the common units, arm’s-length sales of the Company’s equity units (including preferred units), the effect of the rights and preferences of the preferred unit unitholders, and the prospects of a liquidity event. Among other factors are the Company’s financial position and historical financial performance, the status of technological developments within the Company’s research, the composition and ability of the current research and management team, an evaluation or benchmark of the Company’s competition, and the current business climate in the marketplace. Significant changes to the key assumptions underlying the factors used could have resulted in different fair values of the common units and incentive units at each valuation date. Subsequent to the completion of the IPO, the fair value of the Company’s common stock underlying its equity awards is based on the quoted market price of the Company’s common stock on the grant date. The Company estimates the fair value of its stock options using the Black-Scholes option pricing model, which uses as inputs the fair value of the Company’s common stock, and certain management estimates, including the expected stock price volatility, the expected term of the award, the risk-free rate, and expected dividends. Expected volatility is calculated based on reported volatility data for a representative group of publicly traded companies for which historical information is available. The Company selects companies with comparable characteristics with historical share price information that approximates the expected term of the equity-based awards. The Company computes the historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period that approximates the calculated expected term of the stock options. The Company will continue to apply this method until a sufficient amount of historical information regarding the volatility of its stock price becomes available. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant commensurate with the expected term assumption. The Company uses the simplified method, under which the expected term is presumed to be the midpoint between the vesting date and the end of the contractual term. The Company utilizes this method due to lack of historical exercise data. The expected dividend yield is assumed to be zero as the Company has no current plans to pay any dividends on common stock. The Company generally issues equity awards that are subject to either service-based vesting conditions and in limited instances, service-based and performance-based vesting conditions. Compensation expense for awards issued to grantees with service-based vesting conditions are recognized on a straight-line basis based on the grant date fair value over the associated requisite service period of the award, which is generally the vesting term. Compensation expense for awards to grantees with service-based and performance-based vesting conditions are recognized based on the grant-date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable. As of each reporting date, the Company estimates the probability that specified performance criteria will be met and does not recognize compensation expense until it is probable that the performance-based vesting condition will be achieved. The Company evaluates whether an equity award should be classified and accounted for as a liability award or equity award for all equity-based compensation awards granted. As of September 30, 2023, all of the Company’s equity-based awards were equity classified. Forfeitures are recognized as they occur. The Company classifies equity-based compensation expense in the accompanying condensed consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s salary and related costs are classified or in which the award recipient’s service payments are classified, as applicable.
Concentrations of Credit Risk and Significant Suppliers	Concentrations of Credit Risk and Significant Suppliers Financial instruments that potentially expose the Company to credit risk primarily consist of cash and cash equivalents. The Company maintains its cash and cash equivalents with accredited financial institutions and, consequently, the Company does not believe it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Bank accounts in the United States are insured by the Federal Deposit Insurance Corporation (“FDIC”) up to $250,000. As of September 30, 2023 and December 31, 2022, predominantly all of the Company’s primary operating accounts significantly exceeded the FDIC limits. The Company is dependent on third-party organizations to research, develop, manufacture and process its product candidates for its development programs. In particular, the Company relies on one third-party contract manufacturer to produce and process its two most advanced programs, APG777 and APG808, for preclinical and clinical activities. The Company expects to continue to be dependent on a small number of manufacturers to supply it with its requirements for all products. The Company’s research and development programs could be adversely affected by a significant interruption in the supply of the necessary materials. A significant amount of the Company’s research and development activities are performed under its agreements with Paragon (see Note 7).
Off-Balance Sheet Risk	Off-Balance Sheet Risk As of September 30, 2023 and December 31, 2022, the Company had no off-balance sheet risks such as foreign exchange contracts, option contracts or other foreign hedging arrangements.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders' equity that result from transactions and events other than those with stockholders. The Company’s unrealized gains and losses on available-for-sale securities represent the only component of other comprehensive loss that are excluded from the reported net loss and that are presented in the condensed consolidated statements of comprehensive loss.
Net Loss Per Share	Net Loss Per Share The Company follows the two-class method when computing net loss per share. Prior to the Reorganization, the Company issued units that met the definition of participating securities, including the Company’s Series A Preferred Units, the Series B Preferred Units, and vested incentive units (each a participating security), and subsequent to the Reorganization, the Company has two classes of common stock outstanding comprised of voting and non-voting shares. The rights of the holders of voting and non-voting shares are identical, except with respect to voting and conversion. Each share of non-voting stock may be converted into one share of voting stock at any time at the option of the stockholder, subject to certain beneficial ownership limitations. The two-class method determines net loss per unit and net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income for the period to be allocated between common and participating securities based upon their respective rights to share in the income as if all income for the period had been distributed. Prior to the Reorganization, during periods of loss, there was no allocation required under the two-class method since the participating securities did not have a contractual obligation to fund the losses of the Company. Subsequent to the Reorganization, net loss per share for each class of common stock issued is the same as they are entitled to the same liquidation and dividend rights. Prior to the Reorganization, the Company calculated basic net loss per common share by dividing net loss by the weighted-average number of common units outstanding for the period. Subsequent to the Reorganization, the Company calculates basic net loss per common share by dividing net loss by the weighted-average number of common shares outstanding for the period. The Company has generated a net loss in the periods presented so the basic and diluted net loss per unit and net loss per share are the same as the inclusion of the potentially dilutive securities would be anti-dilutive. For periods presented that include the Reorganization, including the three and nine months ended September 30, 2023, the weighted-average shares of common stock outstanding include the weighted average number of common units outstanding prior to the Reorganization.

Available-For-Sale Securities (

Available-For-Sale Securities (Tables)	9 Months Ended
	Sep. 30, 2023
Available-For-Sale Securities
Schedule of Company's investing portfolio	The Company did not hold any available-for-sale securities as of December 31, 2022. The following is a summary of the Company’s investing portfolio as of September 30, 2023 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ AS OF SEPTEMBER 30, 2023 ​ ​ ​ ​ AMORTIZED ​ UNREALIZED ​ ​ ​ COST GAINS LOSSES FAIR VALUE Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. treasury securities ​ $ 59,685 ​ $ 8 ​ $ — ​ $ 59,693 Marketable securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. treasury securities ​ ​ 117,635 ​ ​ 6 ​ ​ (13) ​ ​ 117,628 Debt securities issued by U.S. government agencies ​ 116,823 ​ 148 ​ (14) ​ 116,957 ​ ​ $ 294,143 ​ $ 162 ​ $ (27) ​ $ 294,278

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Measurements
Schedule of financial assets and liabilities measured at fair value on a reoccurring basis	The following table presents information about the Company’s financial assets and liabilities measured at fair value on a reoccurring basis and indicates the level of fair value hierarchy utilized to determine such values as of September 30, 2023 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ AS OF SEPTEMBER 30, 2023 ​ LEVEL 1 LEVEL 2 LEVEL 3 TOTAL Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 103,776 ​ $ — ​ $ — ​ $ 103,776 U.S. treasury securities ​ ​ 59,693 ​ ​ — ​ ​ — ​ ​ 59,693 Marketable securities: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ U.S. treasury securities ​ ​ 117,628 ​ ​ — ​ ​ — ​ ​ 117,628 Debt securities issued by U.S. government agencies ​ — ​ 116,957 ​ — ​ 116,957 ​ ​ $ 281,097 ​ $ 116,957 ​ $ — ​ $ 398,054
Schedule of reconciliation of all assets measured at fair value using Level 3 significant unobservable inputs	The following table provides a reconciliation of all assets and liabilities measured at fair value using Level 3 significant unobservable inputs which were settled during the period from February 4, 2022 (inception) to September 30, 2022 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PREFERRED UNIT PREFERRED UNIT PREFERRED UNIT ​ ​ TRANCHE OPTION ​ TRANCHE OPTION ​ TRANCHE OPTION, ​ ASSET (LIABILITY) NET Balance as of February 4, 2022 (inception) ​ $ — ​ $ — ​ $ — Issuance ​ 650 ​ (1,700) ​ (1,050) Change in fair value ​ ​ (50) ​ ​ (9,100) ​ ​ (9,150) Transfer to temporary equity upon settlement ​ (600) ​ — ​ (600) Balance as of September 30, 2022 ​ $ — ​ $ (10,800) ​ $ (10,800) ​
Schedule of reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs	The following table provides a reconciliation of all assets and liabilities measured at fair value using Level 3 significant unobservable inputs which were settled during the period from February 4, 2022 (inception) to September 30, 2022 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PREFERRED UNIT PREFERRED UNIT PREFERRED UNIT ​ ​ TRANCHE OPTION ​ TRANCHE OPTION ​ TRANCHE OPTION, ​ ASSET (LIABILITY) NET Balance as of February 4, 2022 (inception) ​ $ — ​ $ — ​ $ — Issuance ​ 650 ​ (1,700) ​ (1,050) Change in fair value ​ ​ (50) ​ ​ (9,100) ​ ​ (9,150) Transfer to temporary equity upon settlement ​ (600) ​ — ​ (600) Balance as of September 30, 2022 ​ $ — ​ $ (10,800) ​ $ (10,800) ​

Prepaids and Other Current As_2

Prepaids and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2023
Prepaids and Other Current Assets
Schedule of prepaid expenses and other current assets	Prepaid expenses and other current assets consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ SEPTEMBER 30, DECEMBER 31, ​ ​ 2023 ​ 2022 Prepaid expenses ​ $ 2,156 ​ $ 108 Other current assets ​ 1,411 ​ 57 Total ​ $ 3,567 ​ $ 165 ​

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2023
Accrued Expenses
Schedule of components of accrued expenses	Accrued expenses consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ SEPTEMBER 30, DECEMBER 31, ​ ​ 2023 ​ 2022 Accrued external research and development expenses ​ $ 13,057 ​ $ 8,847 Accrued other ​ 692 ​ 200 Accrued employee compensation ​ 2,221 ​ 515 Total ​ $ 15,970 ​ $ 9,562 ​

Preferred Units (Tables)

Preferred Units (Tables)	9 Months Ended
	Sep. 30, 2023
Preferred Units
Schedule of preferred units	The Company’s preferred units as of December 31, 2022 consisted of the following (in thousands, except unit amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PREFERRED ​ ​ ​ ​ ​ ​ PREFERRED ​ UNITS ​ ​ ​ ​ ​ ​ ​ ​ UNITS ​ ISSUED AND ​ CARRYING ​ LIQUIDATION ​ ​ AUTHORIZED ​ OUTSTANDING ​ VALUE ​ PREFERENCE Series A Preferred Units 20,000,000 20,000,000 ​ $ 28,971 ​ $ 20,000 Series B Preferred Units 45,089,212 45,089,212 ​ 148,496 ​ 149,000 Total 65,089,212 65,089,212 ​ $ 177,467 ​ $ 169,000 ​

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Schedule of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ WEIGHTED- ​ WEIGHTED- ​ AGGREGATE ​ ​ ​ ​ AVERAGE ​ AVERAGE ​ INTRINSIC ​ ​ ​ ​ EXERCISE ​ REMAINING ​ VALUE ​ ​ OPTIONS ​ PRICE CONTRACTUAL TERM (IN THOUSANDS) Outstanding as of December 31, 2022 — ​ $ — ​ ​ — ​ $ — Granted ​ 637,546 ​ $ 20.28 ​ ​ 9.84 ​ $ — Outstanding as of September 30, 2023 ​ 637,546 ​ $ 20.28 ​ ​ 9.84 ​ $ 1,317 Vested and expected to vest as of September 30, 2023 637,546 ​ $ 20.28 ​ ​ 9.84 ​ $ 1,317 Exerciseable as of September 30, 2023 1,389 ​ $ 23.60 ​ ​ 9.89 ​ $ —
Schedule of equity-based compensation expense	The following table presents the classification of equity-based compensation expense related to equity awards granted to employees, managers, executives, and service providers (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ THREE MONTHS NINE MONTHS FEBRUARY 4, 2022 ​ ​ ENDED SEPTEMBER 30, ​ ENDED SEPTEMBER 30, ​ (INCEPTION) to ​ ​ ​ 2023 ​ 2023 ​ SEPTEMBER 30, 2022 ​ Research and development expense ​ $ 417 ​ $ 755 ​ $ — ​ General and administrative expense ​ 1,088 ​ 3,137 ​ — ​ Total ​ $ 1,505 ​ $ 3,892 ​ $ — ​
Incentive Units
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Schedule of fair value assumptions of share based payment	​ ​ ​ ​ ​ ​ NINE MONTHS ​ ​ ENDED ​ ​ ​ SEPTEMBER 30, ​ ​ ​ 2023 ​ Risk free interest rate ​ 4.1% - 4.9% Expected dividend yield ​ 0.0% Expected term (in years) ​ 0.17 – 2 Expected volatility ​ 84% - 90%
Schedule of activity of equity instrument other than option	​ ​ ​ ​ ​ ​ ​ ​ ​ WEIGHTED- ​ ​ ​ ​ AVERAGE ​ ​ NUMBER OF ​ GRANT DATE FAIR ​ ​ UNITS ​ VALUE PER UNIT Unvested incentive units as of December 31, 2022 8,023,288 ​ $ 1.20 Granted ​ 4,621,901 ​ $ 1.32 Vested ​ (922,338) ​ $ 1.54 Exchanged for unvested restricted common stock (11,722,851) ​ $ 1.22 Unvested incentive units as of September 30, 2023 — ​ $ —
Unvested restricted common stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Schedule of activity of equity instrument other than option	​ ​ ​ ​ ​ ​ ​ ​ ​ WEIGHTED- ​ ​ ​ ​ AVERAGE ​ ​ NUMBER OF ​ GRANT DATE FAIR ​ ​ SHARES ​ VALUE PER SHARE Unvested restricted common stock as of December 31, 2022 — ​ $ — Exchange of incentive units ​ 2,779,358 ​ $ 5.16 Vested (122,683) ​ $ 3.78 Unvested restricted common stock as of September 30, 2023 2,656,675 ​ $ 5.22
2023 Equity Incentive Plan | Employee Stock Option
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Schedule of fair value assumptions of share based payment	​ ​ ​ ​ ​ ​ THREE MONTHS ​ ​ ENDED ​ ​ SEPTEMBER 30, ​ 2023 Common stock fair value ​ $17.00 - $23.60 Risk free interest rate ​ 1.8% - 2.1% Expected dividend yield ​ 0.0% Expected term (in years) ​ 5.75 - 6.25 Expected volatility ​ 96.8% - 99.9%

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2023
Net Loss Per Share
Schedule of basic and diluted net loss per share attributable to common unitholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share data): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PERIOD FROM ​ ​ ​ ​ ​ ​ ​ ​ NINE MONTHS FEBRUARY 4 ​ ​ ​ THREE MONTHS ENDED SEPTEMBER 30, ​ ENDED SEPTEMBER 30, ​ (INCEPTION) TO ​ ​ 2023 2022 2023 SEPTEMBER 30, 2022 Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss ​ $ (20,840) ​ $ (19,657) ​ $ (52,250) ​ $ (25,778) ​ Net loss attributable to common stockholders, basic and diluted ​ $ (20,840) ​ $ (19,657) ​ $ (52,250) ​ $ (25,778) ​ Denominator: ​ ​ ​ ​ ​ ​ ​ Weighted average shares of common stock outstanding, basic and diluted ​ ​ 41,231,379 ​ ​ 2,078,804 ​ ​ 17,209,842 ​ ​ 1,516,736 ​ Net loss per share attributable to common stockholders, basic and diluted ​ $ (0.51) ​ $ (9.46) ​ $ (3.04) ​ $ (17.00) ​
Schedule of potential common units excluded from calculation of diluted net loss per share attributable to common unitholders	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ PERIOD FROM ​ ​ ​ ​ ​ ​ NINE MONTHS FEBRUARY 4 ​ ​ ​ THREE MONTHS ENDED SEPTEMBER 30, ​ ENDED ​ (INCEPTION) TO ​ ​ 2023 2022 SEPTEMBER 30, 2023 SEPTEMBER 30, 2022 Series A Preferred Units — ​ 10,000,000 ​ — 10,000,000 ​ Stock options ​ 637,546 ​ — ​ 637,546 ​ — ​ Unvested restricted common stock 2,656,675 ​ — ​ 2,656,675 — ​ Total 3,294,221 ​ 10,000,000 ​ 3,294,221 10,000,000 ​ ​

Nature of the Business (Details

Nature of the Business (Details) $ / shares in Units, $ in Thousands

1 Months Ended

2 Months Ended

3 Months Ended

5 Months Ended

8 Months Ended

9 Months Ended

Jul. 18, 2023 USD ($) $ / shares shares

Nov. 30, 2022 item

Mar. 31, 2022 USD ($)

Sep. 30, 2023 USD ($)

Jun. 30, 2023 USD ($)

Mar. 31, 2023 USD ($)

Sep. 30, 2022 USD ($)

Jun. 30, 2022 USD ($)

Jun. 30, 2022 shares

Sep. 30, 2022 USD ($)

Sep. 30, 2023 USD ($)

Jul. 13, 2023 shares

Dec. 31, 2022 USD ($)

Nature of the Business

Accumulated deficit | $

$ 92,035

$ 92,035

$ 39,785

Net loss | $

$ 4,305

20,840

$ 18,885

$ 12,525

$ 19,657

$ 1,816

$ 25,778

52,250

Negative cash flows from operations | $

7,238

45,007

Cash and cash equivalents | $

188,269

$ 2,583

$ 2,583

188,269

$ 151,890

Marketable securities | $

234,585

234,585

Net proceeds from IPO | $

$ 315,400

Deferred offering costs | $

$ 200

$ 200

IPO

Nature of the Business

Shares issued

20,297,500

Share price | $ / shares

$ 17

Underwriter option to purchase additional number of shares

2,647,500

Common Units

Nature of the Business

Shares issued

1,250,000

Apogee Therapeutics, LLC | Common Units

Nature of the Business

Common stock shares issued

1,919,500

Apogee Therapeutics, LLC | Vested incentive units

Nature of the Business

Common stock shares issued

690,188

Apogee Therapeutics, LLC | Unvested incentive units

Nature of the Business

Common stock shares issued

2,779,358

Apogee Therapeutics, LLC | Series A Preferred Units

Nature of the Business

Nonvoting common stock shares issued

7,678,000

Apogee Therapeutics, LLC | Series B Preferred Units

Nature of the Business

Nonvoting common stock shares issued

5,808,642

Common stock shares issued

11,501,108

Option Agreement | Related party | Paragon Therapeutics, Inc

Nature of the Business

Number of selected targets initially included under the agreement | item

2

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Summary of Significant Accounting Policies
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	$ 0	$ 0
Deferred offering costs	$ 0.2

Available-For-Sale Securities -

Available-For-Sale Securities - Schedule of Company's investing portfolio (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Available-For-Sale Securities
AMORTIZED COST	$ 294,143
UNREALIZED GAINS	162
UNREALIZED LOSSES	(27)
FAIR VALUE	294,278
U.S. treasury securities | Cash equivalents :
Available-For-Sale Securities
AMORTIZED COST	59,685
UNREALIZED GAINS	8
FAIR VALUE	59,693
U.S. treasury securities | Marketable securities
Available-For-Sale Securities
AMORTIZED COST	117,635
UNREALIZED GAINS	6
UNREALIZED LOSSES	(13)
FAIR VALUE	117,628
Debt securities issued by U.S. government agencies | Marketable securities
Available-For-Sale Securities
AMORTIZED COST	116,823
UNREALIZED GAINS	148
UNREALIZED LOSSES	(14)
FAIR VALUE	$ 116,957

Available-For-Sale Securities_2

Available-For-Sale Securities (Details) $ in Millions	Sep. 30, 2023 USD ($) security
Available-For-Sale Securities
Number of securities in unrealized loss position, less than 12 months | security	7
Value of securities in unrealized loss position, less than 12 months	$ 71.4
Allowance for credit loss	$ 0

Fair Value Measurements - Measu

Fair Value Measurements - Measured at fair value on reoccurring basis (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities, Current	$ 234,585
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities, Current	398,054
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities, Current	281,097
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities, Current	116,957
Fair Value, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	103,776
Fair Value, Recurring [Member] | Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	103,776
Fair Value, Recurring [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	59,693
Marketable Securities, Current	117,628
Fair Value, Recurring [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	59,693
Marketable Securities, Current	117,628
Fair Value, Recurring [Member] | US Treasury and Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities, Current	116,957
Fair Value, Recurring [Member] | US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities, Current	$ 116,957

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Thousands	8 Months Ended
	Sep. 30, 2022 USD ($)
PREFERRED UNIT TRANCHE OPTION ASSET, reconciliation
Issuance	$ 650
Change in fair value	(50)
Transfer to temporary equity upon settlement	(600)
PREFERRED UNIT TRANCHE OPTION (LIABILITY), reconciliation
Issuance	(1,700)
Change in fair value	(9,100)
Balance as of end	(10,800)
Issuance	(1,050)
Change in fair value	(9,150)
Balance as of ending	$ (10,800)

Prepaids and Other Current As_3

Prepaids and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Prepaids and Other Current Assets
Prepaid expenses	$ 2,156	$ 108
Deferred offering costs	200
Other current assets	1,411	57
Total	$ 3,567	$ 165

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Accrued Expenses
Accrued external research and development expenses	$ 13,057	$ 8,847
Accrued other	692	200
Accrued employee compensation	2,221	515
Total	$ 15,970	$ 9,562

Other Significant Agreements _2

Other Significant Agreements Paragon Option Agreement (Details) $ in Thousands		1 Months Ended		3 Months Ended			8 Months Ended	9 Months Ended	11 Months Ended
		Nov. 30, 2023 USD ($)	Nov. 30, 2022 USD ($) item shares	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($) shares	Sep. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) shares	Sep. 30, 2023 USD ($) shares	Dec. 31, 2022 USD ($) shares
Other Significant Agreements Paragon Option Agreement
Issued total common units (in shares) | shares					50,674,296			50,674,296	50,674,296	0
Research and development	[1]				$ 17,069	$ 9,885	$ 15,578	$ 39,470
Option Agreement
Other Significant Agreements Paragon Option Agreement
Payments due upon exercise of option		$ 0								$ 0
Aggregate acquisition cost			$ 2,900
Paragon Therapeutics, Inc | Related party
Other Significant Agreements Paragon Option Agreement
Research and development					6,600	9,600	15,200	21,100
Paragon Therapeutics, Inc | Option Agreement
Other Significant Agreements Paragon Option Agreement
Termination period of agreement		30 days	30 days
Period of material breach			30 days
Paragon Therapeutics, Inc | Option Agreement | Related party
Other Significant Agreements Paragon Option Agreement
Number of selected targets initially included under the agreement | item			2
Upfront cash amount paid			$ 1,300
Issued common units (in shares) | shares			1,250,000
Issued total common units (in shares) | shares			5,000,000
Aggregate fair value on grant date			$ 2,200
Non-refundable fee		$ 2,000	$ 500
Research and development					4,400	9,600	15,500	12,100
Paragon Therapeutics, Inc | Option Agreement | Maximum | Related party
Other Significant Agreements Paragon Option Agreement
Issued total common units (in shares) | shares			3,750,000
Paragon Therapeutics, Inc | Paragon IL13 License Agreement
Other Significant Agreements Paragon Option Agreement
Research and development					2,300	$ 0	$ 0	$ 9,100
Maximum amount of achievement of development and clinical mile stones			$ 3,000
Nomination fee paid			1,000		$ 2,000				$ 3,000
Milestone payments due				$ 1,000
Milestone payment of trial payable			$ 2,000
Expiration period of commercial sale			12 years
Termination period of agreement			60 days
Period of material breach			90 days
Threshold number of days for termination upon failure to make payment and such failure persists even after the notice			30 days
[1] Includes related-party amounts of $6,624 for the three months ended September 30, 2023, $9,596 for the three months ended September 30, 2022, $21,083 for the nine months ended September 30, 2023 and $15,219 for the period from February 4, 2022 (inception) to September 30, 2022.

Other Significant Agreements _3

Other Significant Agreements Paragon Option Agreement - WuXi Biologics (Hong Kong) limited agreements (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended
		Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2023
Other Significant Agreements Paragon Option Agreement
Research and development	[1]		$ 17,069	$ 9,885	$ 15,578	$ 39,470
Cell Line License Agreement | WuXi Biologics
Other Significant Agreements Paragon Option Agreement
Prior notice period for termination of work order		6 months
Non-refundable license fee		$ 150
Threshold number of days for no termination or cancellation fee upon uncured breach after notice of such breach		60 days
Threshold number of days for termination upon uncured material breach after notice of such breach		30 days
Biologics Master Services Agreement | WuXi Biologics
Other Significant Agreements Paragon Option Agreement
Prior notice period for termination of work order		6 months
Threshold number of days for no termination or cancellation fee upon uncured breach after notice of such breach		30 days
Threshold number of days for no termination or cancellation fee upon performance breach		90 days
Research and development			$ 6,400			$ 9,600
[1] Includes related-party amounts of $6,624 for the three months ended September 30, 2023, $9,596 for the three months ended September 30, 2022, $21,083 for the nine months ended September 30, 2023 and $15,219 for the period from February 4, 2022 (inception) to September 30, 2022.

Preferred Units (Details)

Preferred Units (Details) - USD ($) $ / shares in Units, $ in Millions				9 Months Ended
	Jul. 18, 2023	Nov. 15, 2022	Feb. 24, 2022	Sep. 30, 2023	Dec. 31, 2022
Preferred Units
Preferred Units, units authorized					65,089,212
Preferred Units, units converted	24,987,750			72,570,755
Preferred Units, units issued					65,089,212
Preferred Units, units outstanding					65,089,212
Series A Preferred Units
Preferred Units
Preferred Units, units authorized					20,000,000
Preferred Units, units issued					20,000,000
Preferred Units, units outstanding					20,000,000
Series A Preferred Units | Tranche Option
Preferred Units
Initial proceeds of issuance of preferred units			$ 1.1
Series A Preferred Units | Series A Agreement
Preferred Units
Preferred Units, units issued			5,000,000
Maximum number of issue and sell of preferred shares			20,000,000
Preferred units purchase price (in dollars per share)			$ 1
Gross cash proceeds			$ 5
Net issuance cost			$ 0.2
Series A Preferred Units | Series A Agreement | Tranche Option
Preferred Units
Preferred Units, units issued			5,000,000
Gross cash proceeds			$ 20
Series B Preferred Units
Preferred Units
Preferred Units, units authorized					45,089,212
Preferred Units, units issued					45,089,212
Preferred Units, units outstanding					45,089,212
Series B Preferred Units | Series B Agreement
Preferred Units
Maximum number of issue and sell of preferred shares		45,089,212
Temporary equity preferred shares purchase price (in dollars per share)		$ 3.30456
Gross cash proceeds		$ 149
Net issuance cost		$ 0.5

Preferred Units - Schedule of p

Preferred Units - Schedule of preferred units (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Preferred Units
PREFERRED UNITS AUTHORIZED		65,089,212
PREFERRED UNITS ISSUED		65,089,212
PREFERRED UNITS OUTSTANDING		65,089,212
CARRYING VALUE		$ 177,467
LIQUIDATION PREFERENCE		$ 169,000
Series A Preferred Units
Preferred Units
PREFERRED UNITS AUTHORIZED		20,000,000
PREFERRED UNITS ISSUED		20,000,000
PREFERRED UNITS OUTSTANDING		20,000,000
CARRYING VALUE	$ 28,971	$ 28,971
LIQUIDATION PREFERENCE	20,000	$ 20,000
Series B Preferred Units
Preferred Units
PREFERRED UNITS AUTHORIZED		45,089,212
PREFERRED UNITS ISSUED		45,089,212
PREFERRED UNITS OUTSTANDING		45,089,212
CARRYING VALUE	148,496	$ 148,496
LIQUIDATION PREFERENCE	$ 149,000	$ 149,000

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - $ / shares		3 Months Ended		8 Months Ended	9 Months Ended
	Jul. 18, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2023	Dec. 31, 2022
Subsidiary, Sale of Stock [Line Items]
Preferred Units, units converted	24,987,750				72,570,755
Common stock, shares authorized	400,000,000	400,000,000			400,000,000	0
Common stock, par value	$ 0.00001	$ 0.00001			$ 0.00001
Common stock, shares outstanding		48,017,621			48,017,621	0
Common stock, shares, issued		50,674,296			50,674,296	0
Antidilutive units		3,294,221	10,000,000	10,000,000	3,294,221
Common Units, units authorized		0			0	5,000,000
Common Units, units issued		5,000,000			5,000,000	5,000,000
Common Units, units outstanding		5,000,000			5,000,000	5,000,000
Unvested restricted common stock
Subsidiary, Sale of Stock [Line Items]
Antidilutive units		2,656,675			2,656,675
Voting Common Stock
Subsidiary, Sale of Stock [Line Items]
Common stock, shares, issued		37,187,654			37,187,654
Nonvoting Common Stock
Subsidiary, Sale of Stock [Line Items]
Common stock, shares, issued		13,486,642			13,486,642
IPO
Subsidiary, Sale of Stock [Line Items]
Shares issued	20,297,500

Equity-Based Compensation - Det

Equity-Based Compensation - Determining fair value of incentive units (Details) - Incentive Units	9 Months Ended
	Sep. 30, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Risk free interest rate, Minimum	4.10%
Risk free interest rate, Maximum	4.90%
Expected dividend yield	0%
Expected volatility, Minimum	84%
Expected volatility, Maximum	90%
Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term	2 months 1 day
Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term	2 years

Equity-Based Compensation - Sum

Equity-Based Compensation - Summary of Company's incentive unit activity (Details) - $ / shares	1 Months Ended	9 Months Ended
	Aug. 31, 2023	Sep. 30, 2023
NUMBER OF UNITS
Granted	100,000
Incentive Units
NUMBER OF UNITS
Beginning balance		8,023,288
Granted		4,621,901
Vested		(922,338)
Exchanged for unvested common stock		(11,722,851)
WEIGHTED-AVERAGE GRANT DATE FAIR VALUE PER UNIT
Beginning balance (in dollars per share)		$ 1.20
Granted (in dollars per share)		1.32
Vested (in dollars per share)		1.54
Exchanged for unvested common stock (in dollars per share)		$ 1.22

Equity-Based Compensation - S_2

Equity-Based Compensation - Summary of Company's Unvested Restricted Common Stock Award Activity (Details) - Unvested restricted common stock - $ / shares		9 Months Ended
	Feb. 04, 2022	Sep. 30, 2023
NUMBER OF UNITS
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Exchange Of Incentive Units	2,779,358	2,779,358
Vested		(122,683)
Ending balance		2,656,675
WEIGHTED-AVERAGE GRANT DATE FAIR VALUE PER UNIT
Exchange of incentive units		$ 5.16
Vested (in dollars per share)		3.78
Ending balance (in dollars per share)		$ 5.22

Equity-Based Compensation - D_2

Equity-Based Compensation - Determining fair value of stock options (Details) - 2023 Equity Incentive Plan - Employee Stock Option	3 Months Ended
	Sep. 30, 2023 $ / shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Risk free interest rate, Minimum	1.80%
Risk free interest rate, Maximum	2.10%
Expected dividend yield	0%
Expected volatility, Minimum	96.80%
Expected volatility, Maximum	99.90%
Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock fair value (in dollars per share)	$ 17
Expected term	5 years 9 months
Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock fair value (in dollars per share)	$ 23.60
Expected term	6 years 3 months

Equity-Based Compensation - S_3

Equity-Based Compensation - Summary of stock option activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares
OPTIONS
Granted | shares	637,546
Outstanding as of ending | shares	637,546
Vested and expected to vest | shares	637,546
Exercisable | shares	1,389
WEIGHTED-AVERAGE EXERCISE PRICE
Granted (in dollars per share) | $ / shares	$ 20.28
Outstanding as of ending (in dollars per share) | $ / shares	20.28
Vested and expected to vest (in dollars per share) | $ / shares	20.28
Exercisable (in dollars per share) | $ / shares	$ 23.60
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding weighted-average remaining contractual term (in years)	9 years 10 months 2 days
Granted weighted-average remaining contractual term (in years)	9 years 10 months 2 days
Vested and expected to vest weighted-average remaining contractual term (in years)	9 years 10 months 2 days
Exercisable weighted-average remaining contractual term	9 years 10 months 20 days
Outstanding aggregate intrinsic value | $	$ 1,317
Vested and expected to vest aggregate intrinsic value | $	$ 1,317

Equity-Based Compensation - S_4

Equity-Based Compensation - Summary of classification of equity-based compensation expense related to incentive units (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	Aug. 31, 2023	Sep. 30, 2023	Sep. 30, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Equity-based compensation expense	$ 0	$ 1,505	$ 3,892
Research and development expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Equity-based compensation expense		417	755
General and administrative expense
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Equity-based compensation expense		$ 1,088	$ 3,137

Equity-Based Compensation - Add

Equity-Based Compensation - Additional Information (Details) $ in Thousands		1 Months Ended		3 Months Ended	8 Months Ended	9 Months Ended
	Feb. 04, 2022 shares	Aug. 31, 2023 USD ($) Option shares	Jul. 31, 2023 shares	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) shares
Equity-Based Compensation
Vesting period (in years)		3 years
Shares converted	3,469,546
Granted		100,000
Unrecognized compensation expense | $				$ 21,400		$ 21,400
Share based compensation recognition period						3 years
Additional equity-based compensation expense | $					$ 1,700
Number of stock option grants | Option		2
Granted						637,546
Equity-based compensation expense | $		$ 0		$ 1,505		$ 3,892
Incentive Units
Equity-Based Compensation
Vesting period (in years)						4 years
Granted						4,621,901
Incentive Units | Tranche One [Member]
Equity-Based Compensation
Vesting period (in years)						12 months
Vesting (as percentage)						25%
Incentive Units | Tranche Two [Member]
Equity-Based Compensation
Vesting period (in years)						36 months
Vesting (as percentage)						75%
Unvested restricted common stock
Equity-Based Compensation
Exchange of incentive units	2,779,358					2,779,358
2023 Equity Incentive Plan
Equity-Based Compensation
Common stock reserved for issuance			6,706,037
Increase in shares available for grand (as percentage)			5%
Granted		50,000
2023 Employee Stock Purchase Plan
Equity-Based Compensation
Common stock reserved for issuance			479,003
Granted						0

Related Parties (Details)

Related Parties (Details) - USD ($) $ in Thousands		3 Months Ended		8 Months Ended	9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2023	Dec. 31, 2022
Related Parties
Research and development	[1]	$ 17,069	$ 9,885	$ 15,578	$ 39,470
General and administrative	[2]	7,236	622	1,050	16,378
Related party | Paragon Therapeutics, Inc
Related Parties
Due to related party		6,600			6,600	$ 8,000
Research and development		$ 6,600	$ 9,600	$ 15,200	$ 21,100
[1] Includes related-party amounts of $6,624 for the three months ended September 30, 2023, $9,596 for the three months ended September 30, 2022, $21,083 for the nine months ended September 30, 2023 and $15,219 for the period from February 4, 2022 (inception) to September 30, 2022. Includes related-party amounts of $9 for the three months ended September 30, 2023, none for the three months ended September 30, 2022, $53 for the nine months ended September 30, 2023 and $273 for the period from February 4, 2022 (inception) to September 30, 2022.

Net Loss Per Unit - Basic and d

Net Loss Per Unit - Basic and diluted net loss per unit attributable to common unitholders (Details) - USD ($) $ / shares in Units, $ in Thousands	2 Months Ended	3 Months Ended					8 Months Ended	9 Months Ended
	Mar. 31, 2022	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2022	Sep. 30, 2023
Numerator:
Net Income (Loss)	$ (4,305)	$ (20,840)	$ (18,885)	$ (12,525)	$ (19,657)	$ (1,816)	$ (25,778)	$ (52,250)
Net loss attributable to common unitholders, basic		(20,840)			(19,657)		(25,778)	(52,250)
Net loss attributable to common unitholders, diluted		$ (20,840)			$ (19,657)		$ (25,778)	$ (52,250)
Denominator:
Weighted-average common units outstanding, basic		41,231,379			2,078,804		1,516,736	17,209,842
Weighted-average common units outstanding, diluted		41,231,379			2,078,804		1,516,736	17,209,842
Net loss per unit attributable to common unitholders, basic		$ (0.51)			$ (9.46)		$ (17)	$ (3.04)
Net loss per unit attributable to common unitholders, diluted		$ (0.51)			$ (9.46)		$ (17)	$ (3.04)

Net Loss Per Unit - Potential c

Net Loss Per Unit - Potential common units excluded from calculation of diluted net loss per unit attributable to common unitholders (Details) - shares	3 Months Ended		8 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2022	Sep. 30, 2023
Net Loss Per Unit
Antidilutive units	3,294,221	10,000,000	10,000,000	3,294,221
Series A Preferred Units
Net Loss Per Unit
Antidilutive units		10,000,000	10,000,000
Employee Stock Option
Net Loss Per Unit
Antidilutive units	637,546			637,546
Unvested restricted common stock
Net Loss Per Unit
Antidilutive units	2,656,675			2,656,675

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) $ in Millions	1 Months Ended
	Nov. 30, 2023 USD ($)
Subsequent Events | Paragon Therapeutics, Inc | IL-4R License Agreement
Subsequent Events
Milestone payment	$ 1

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	2 Months Ended	3 Months Ended					8 Months Ended	9 Months Ended
	Mar. 31, 2022	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2022	Sep. 30, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (4,305)	$ (20,840)	$ (18,885)	$ (12,525)	$ (19,657)	$ (1,816)	$ (25,778)	$ (52,250)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Sep. 30, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false