Related Party Transactions

3 Months Ended

Mar. 31, 2026

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 License Agreements and other Paragon reimbursable expenses, which are ultimately settled in cash (in millions) and recorded within Research and development in the consolidated statement of operations for the periods presented:

	Three Months Ended March 31,
	2026		2025
License Agreements milestone and sublicensing fees	$	3.0	$	2.5
Other Paragon reimbursable expenses	0.1		—
Total related party expense (excludes stock-based compensation)	$	3.1	$	2.5

The following is the summary of Related party accounts payable and other current liabilities (in millions):

	March 31, 2026		December 31, 2025
Other Paragon reimbursable expenses	$	0.1	$	—
Total related party accounts payable	$	0.1	$	—

For the three months ended March 31, 2026 and 2025, the Company recognized $0.1 million and de minimis, respectively, of Paragon reimbursable expenses, which were recorded as Research and development expenses in the consolidated statements of operations.

For the three months ended March 31, 2026 and 2025, the Company made payments totaling de minimis and $0.1 million, respectively, in connection with Paragon reimbursable expenses.

Paragon License Agreements

See Note 6 for disclosures related to the License Agreements entered into with Paragon.

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 2016 Plan (as defined in Note 9) 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 36 equal monthly installments, subject to Mr. McKenna’s continued service to the Company through each applicable vesting date. The Company recognized stock-based compensation expense related to Mr. McKenna's consulting agreement of $0.3 million for the three months ended March 31, 2026 and 2025, respectively.