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Related Party Transactions
 12 Months Ended
Dec. 31, 2025
Related Party Transactions [Abstract]  
Related Party Transactions Related Party Transactions
Paragon and Parapyre each beneficially own less than 5% of a class of the Company's voting securities through their respective holdings of the Company's common stock. Fairmount Funds Management LLC ("Fairmount") beneficially owns more than 5% of a class of the Company's voting securities, has two seats on the Board (held by Peter Harwin and Tomas Kiselak) and beneficially owns more than 5% of Paragon. Fairmount appointed Paragon's board of directors and has the contractual right to approve the appointment of any executive officers of Paragon. Parapyre is an entity formed by Paragon as a vehicle to hold equity in Spyre
in order to share profits with certain employees of Paragon and will not perform any substantive role under the Paragon Agreement other than to receive warrants granted to Parapyre under the Paragon Agreement.
The following is the summary of expenses related to the Paragon Agreement and License Agreements, which are ultimately settled in cash (in millions) and recorded within Research and development in the consolidated statement of operations for the periods presented:
Year Ended December 31,
202520242023
Reimbursable costs under the Paragon Agreement$0.1 $15.3 $37.1 
License Agreements milestone and sublicensing fees10.4 10.2 — 
Total related party expense (excludes stock comp)$10.5 $25.5 $37.1 

The following is the summary of Related party accounts payable and other current liabilities (in millions):
December 31,
20252024
Reimbursable costs under the Paragon Agreement$— $0.1 
License Agreements development milestone liability (see Note 9)
— 0.5 
Total related party accounts payable$— $0.6 
Paragon Agreement
In connection with the Asset Acquisition, the Company assumed the rights and obligations of Pre-Merger Spyre under the Paragon Agreement. Under the Paragon Agreement, Spyre is obligated to compensate Paragon for its services performed under each research program based on the actual costs incurred with mark-up costs pursuant to the terms of the Paragon Agreement. As of the date of the Asset Acquisition, Pre-Merger Spyre had incurred total expenses of $19.0 million under the Paragon Agreement since inception, which included the $3.0 million research initiation fee and $16.0 million of reimbursable expenses under the Paragon Agreement for historical costs owed to Paragon. As of the acquisition date, $19.0 million was unpaid and was assumed by the Company through the Asset Acquisition. The Paragon Agreement was amended and restated on September 29, 2023 and May 14, 2024. Please refer to Note 8 for additional information on the Paragon Agreement.
On July 12, 2023, December 14, 2023, and June 5, 2024, the Company exercised the Option available under the Paragon Agreement with respect to the SPY001, SPY002 and SPY003 research programs, respectively. The Option with respect to one additional program remains unexercised under the Paragon Agreement. Please refer to Note 9 for additional information on the License Agreements related to the exercised options.
On May 14, 2024, the Company, Paragon and Parapyre entered into a second amended and restated antibody discovery and option agreement that amends and restates that certain amended and restated antibody discovery and option agreement, dated September 29, 2023, by and between Paragon, Parapyre and Spyre Therapeutics, LLC, in order to, among other things, (i) replace the Company’s subsidiary with the Company as a party to the agreement and (ii) amend certain terms related to the SPY003 research program, including without limitation, (a) establishing an SPY003 antibody selection process pursuant to which the Company and Paragon shall alternate in turn to select a project antibody to be included and excluded, respectively, from the Company’s rights under its option to license certain intellectual property rights related to SPY003 from Paragon until all project antibodies under the SPY003 research program have been selected; (b) reducing the development costs invoiced to the Company for the SPY003 research program incurred from and after April 1, 2024 through completion of the SPY003 antibody selection process by 50%; (c) requiring Paragon to reimburse the Company for 50% of the development costs for the SPY003 research program incurred prior to April 1, 2024; provided, that Paragon receives rights to at least one SPY003 project antibody following completion of the SPY003 antibody selection process; (d) obligating the Company to exercise its option to license the intellectual property rights to SPY003 project antibodies and technology following the completion of the SPY003 antibody selection
process; and (e) establishing a license agreement term sheet for the SPY003 research program with substantially similar milestone payment terms and royalty payment terms as the SPY001 License Agreement. Please refer to Note 9 for additional disclosures.
For the years ended December 31, 2025, 2024 and 2023, the Company recognized expenses related to services provided by Paragon subsequent to the Asset Acquisition totaling $0.1 million and $29.8 million and $48.5 million, which included nil , $14.5 million and $11.4 million of stock-based compensation expense, respectively, and were recorded as Research and development expenses in the consolidated statements of operations. Included within the expenses recognized for services provided by Paragon for the year ended December 31, 2024, is a $5.9 million reduction in Research and development expenses related to the reimbursement of 50% of the development costs for the SPY003 research program by Paragon.
For the years ended December 31, 2025, 2024 and 2023, the Company made payments totaling $0.2 million and $31.8 million and $39.5 million, respectively, to Paragon.
Parapyre Option Obligation
Pursuant to the Paragon Agreement, the Company issued Parapyre an annual equity grant of warrants, on the last business day of each of the years ended December 31, 2023 and December 31, 2024, to purchase 1% of the then outstanding shares of the Company's common stock, on a fully diluted basis, during the term of the Paragon Agreement. See Note 15 for disclosures related to the Parapyre Option Obligation.
Paragon License Agreements
See Note 9 for disclosures related to the License Agreements entered into with Paragon.
December 2023 PIPE
On December 11, 2023, the Company completed December 2023 PIPE. The December 2023 PIPE Investors included Fairmount, a related party. Fairmount's participation in the December 2023 PIPE was approved by the Company's board of directors. Fairmount's investment accounted for $10.0 million of the $180.0 million gross proceeds raised in the December 2023 PIPE. See Note 1 for disclosures related to the December 2023 PIPE.
Mark McKenna Option Grant
On February 1, 2024, the Board appointed Mark McKenna as a Class I director. Mr. McKenna and the Company are parties to a consulting agreement, pursuant to which Mr. McKenna agreed to continue to provide consulting services as an independent contractor to the Company, with an effective date of August 1, 2023 (the “Vesting Commencement Date”). As compensation for Mr. McKenna’s consulting services, on November 22, 2023, he was granted non-qualified stock options to purchase 477,000 shares of the Company’s common stock under the Company's equity incentive plan with an exercise price of $10.39 per share, which vest as to 25% on the one year anniversary of the Vesting Commencement Date and thereafter vest and become exercisable in 48th equal monthly installments, subject to Mr. McKenna’s continued service to the Company through each applicable vesting date. For the years ended December 31, 2025, 2024 and 2023, the Company recognized $1.0 million, $1.1 million and $0.1 million, respectively, in stock-based compensation expense related to Mr. McKenna's consulting agreement.