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Form SCHEDULE 13D/A Spyre Therapeutics, Inc. Filed by: Fairmount Funds Management LLC

April 20, 2026 6:00 PM





If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).




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SCHEDULE 13D




Comment for Type of Reporting Person:
The securities include (i) 4,018,101 shares of common stock, $0.0001 par value per share (the "Common Stock") and (ii) 4,166,840 shares of Common Stock issuable upon conversion of 104,171 shares of Series A Preferred Stock, par value $0.0001 per share (the "Series A Preferred Stock"), held directly by Fairmount Healthcare Fund II L.P. ("Fund II"). The securities exclude shares of Common Stock issuable upon conversion of shares of Series A Preferred Stock and Series B Preferred Stock, par value $0.0001 per share (the "Series B Preferred Stock") held directly by Fund II in excess of the beneficial ownership limitation of 9.99%. Row 13 is based on 90,060,297 shares of Common Stock outstanding as of April 16, 2026, consisting of (i) 85,664,811 shares of Common Stock outstanding as of April 16, 2026, as reported in the Company's final prospectus supplement filed pursuant to Rule 424(b)(5) dated April 14, 2026, (ii) 228,646 shares underlying options that are currently exercisable or will be exercisable within 60 days of the date of this filing by the Reporting Persons and (iii) 4,166,840 shares of Common Stock underlying the 104,171 shares of Series A Preferred Stock owned by Fund II, applying the beneficial ownership limitation.


SCHEDULE 13D




Comment for Type of Reporting Person:
The securities include (i) 4,018,101 shares of Common Stock and (ii) 4,166,840 shares of Common Stock issuable upon conversion of 104,171 shares of Series A Preferred Stock held directly by Fund II. The securities exclude shares of Common Stock issuable upon conversion of shares of Series A Preferred Stock and Series B Preferred Stock held directly by Fund II in excess of the beneficial ownership limitation of 9.99%. Row 13 is based on 90,060,297 shares of Common Stock outstanding as of April 16, 2026, consisting of (i) 85,664,811 shares of Common Stock outstanding as of April 16, 2026, as reported in the Company's final prospectus supplement filed pursuant to Rule 424(b)(5) dated April 14, 2026, (ii) 228,646 shares underlying options that are currently exercisable or will be exercisable within 60 days of the date of this filing by the Reporting Persons and (iii) 4,166,840 shares of Common Stock underlying the 104,171 shares of Series A Preferred Stock owned by Fund II, applying the beneficial ownership limitation.


SCHEDULE 13D




Comment for Type of Reporting Person:
The securities include (a) 406,038 shares of Common Stock held directly by Mr. Harwin, (b) 114,323 shares of Common Stock issuable upon the exercise of options that are currently exercisable or will be exercisable within 60 days of the date of this filing held directly by Mr. Harwin*, and (c) Fund II's direct holdings of (i) 4,018,101 shares of Common Stock and (ii) 4,478,240 shares of Common Stock issuable upon conversion of 111,956 shares of Series A Preferred Stock held directly by Fund II. The securities exclude shares of Common Stock issuable upon conversion of shares of Series A Preferred Stock and Series B Preferred Stock held directly by Fund II in excess of the beneficial ownership limitation of 9.99%. Row 13 is based on 90,257,374 shares of Common Stock outstanding as of April 16, 2026, consisting of (i) 85,664,811 shares of Common Stock outstanding as of April 16, 2026, as reported in the Company's final prospectus supplement filed pursuant to Rule 424(b)(5) dated April 14, 2026, (ii) 114,323 shares of Common Stock underlying options that are currently exercisable or will be exercisable within 60 days of the date of this filing by Mr. Harwin and (iii) 4,478,240 shares of Common Stock underlying the 111,956 shares of Series A Preferred Stock owned by Fund II, applying the beneficial ownership limitation. * Under Mr. Harwin's arrangement with Fairmount, Mr. Harwin holds the options for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). Mr. Harwin is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. Mr. Harwin therefore disclaims beneficial ownership of the option and underlying common stock.


SCHEDULE 13D




Comment for Type of Reporting Person:
The securities include (a) 406,038 shares of Common Stock held directly by Mr. Kiselak, (b) 114,323 shares of Common Stock issuable upon the exercise of options that are currently exercisable or will be exercisable within 60 days of the date of this filing held directly by Mr. Kiselak*, and (c) Fund II's direct holdings of (i) 4,018,101 shares of Common Stock and (ii) 4,478,240 shares of Common Stock issuable upon conversion of 111,956 shares of Series A Preferred Stock held directly by Fund II. The securities exclude shares of Common Stock issuable upon conversion of shares of Series A Preferred Stock and Series B Preferred Stock held directly by Fund II in excess of the beneficial ownership limitation of 9.99%. Row 13 is based on 90,257,374 shares of Common Stock outstanding as of April 16, 2026, consisting of (i) 85,664,811 shares of Common Stock outstanding as of April 16, 2026, as reported in the Company's final prospectus supplement filed pursuant to Rule 424(b)(5) dated April 14, 2026, (ii) 114,323 shares of Common Stock underlying options that are currently exercisable or will be exercisable within 60 days of the date of this filing by Mr. Kiselak and (iii) 4,478,240 shares of Common Stock underlying the 111,956 shares of Series A Preferred Stock owned by Fund II, applying the beneficial ownership limitation. * Under Mr. Kiselak's arrangement with Fairmount, Mr. Kiselak holds the options for one or more investment vehicles managed by Fairmount (each, a "Fairmount Fund"). Mr. Kiselak is obligated to turn over to Fairmount any net cash or stock received from the option for the benefit of such Fairmount Fund. Mr. Kiselak therefore disclaims beneficial ownership of the option and underlying common stock.


SCHEDULE 13D


Fairmount Funds Management LLC
Signature:/s/ Peter Harwin
Name/Title:Peter Harwin, Managing Member
Date:04/20/2026
Signature:/s/ Tomas Kiselak
Name/Title:Tomas Kiselak, Managing Member
Date:04/20/2026
Fairmount Healthcare Fund II L.P.
Signature:/s/ Peter Harwin
Name/Title:Peter Harwin, Managing Member
Date:04/20/2026
Signature:/s/ Tomas Kiselak
Name/Title:Tomas Kiselak, Managing Member
Date:04/20/2026
Peter Harwin
Signature:/s/ Peter Harwin
Name/Title:Peter Harwin
Date:04/20/2026
Tomas Kiselak
Signature:/s/ Tomas Kiselak
Name/Title:Tomas Kiselak
Date:04/20/2026

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