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SCHEDULE 13D/A 0001104659-23-083070 0001802528 XXXXXXXX LIVE 4 Common Stock, $0.00001 par value 01/22/2026 false 0001974640 03770N101 Apogee Therapeutics, Inc. 221 Crescent Street Building 17, Suite 102b Waltham MA 02453 Ms. Erin O'Connor (267) 262-5300 Fairmount Funds Management LLC 200 Barr Harbor Drive, Suite 400 West Conshohocken PA 19428 0001802528 N Fairmount Funds Management LLC a AF N DE 0.00 5948385.00 0.00 5948385.00 5948385.00 N 9.82 IA The securities include (i) 298,647 shares of common stock, $0.00001 par value per share (the "Common Stock") and (ii) 5,649,738 shares of Common Stock issuable upon conversion of 5,649,738 shares of Non-Voting Common Stock, par value $0.00001 per share (the "Non-Voting Common Stock"), the conversion of which is subject to a beneficial ownership limitation of 9.99% of the outstanding Common Stock, both directly held by Fairmount Healthcare Fund II L.P., a Delaware limited partnership ("Fund II"). The securities exclude shares of Common Stock issuable upon conversion of shares of Non-Voting Common Stock held by Fund II in excess of the beneficial ownership limitation. Row 13 is based on 60,567,741 shares of Common Stock outstanding as of January 22, 2026, consisting of (i) 54,833,587 shares of Common Stock outstanding as of November 3, 2025, as reported in the Company's Form 10-Q filed on November 10, 2025, (ii) 84,416 shares underlying vested stock options owned by the Reporting Persons and (iii) 5,649,738 shares of Common Stock underlying the 5,649,738 shares of Non-Voting Common Stock owned by Fund II, applying the beneficial ownership limitation. 0001769651 N Fairmount Healthcare Fund II L.P. a AF N DE 0.00 5948385.00 0.00 5948385.00 5948385.00 N 9.82 PN The securities include (i) 298,647 shares of Common Stock and (ii) 5,649,738 shares of Common Stock issuable upon conversion of 5,649,738 shares of Non-Voting Common Stock, the conversion of which is subject to a beneficial ownership limitation of 9.99% of the outstanding Common Stock, both directly held by Fund II. The securities exclude shares of Common Stock issuable upon conversion of shares of Non-Voting Common Stock held by Fund II in excess of the beneficial ownership limitation. Row 13 is based on 60,567,741 shares of Common Stock outstanding as of January 22, 2026, consisting of (i) 54,833,587 shares of Common Stock outstanding as of November 3, 2025, as reported in the Company's Form 10-Q filed on November 10, 2025, (ii) 84,416 shares underlying vested stock options owned by the Reporting Persons and (iii) 5,649,738 shares of Common Stock underlying the 5,649,738 shares of Non-Voting Common Stock owned by Fund II, applying the beneficial ownership limitation. 0001663607 N Peter Evan Harwin a AF N X1 93374.00 5953653.00 93374.00 5953653.00 6047027.00 N 9.99 IN HC The securities include (a) 51,166 shares of Common Stock held directly by Mr. Harwin, (b) 42,208 shares of Common Stock underlying vested options held by Mr. Harwin* and (c) Fund II's direct holdings of (i) 298,647 shares of Common Stock and (ii) 5,655,066 shares of Common Stock issuable upon conversion of 5,655,066 shares of Non-Voting Common Stock, the conversion of which is subject to a beneficial ownership limitation of 9.99% of the outstanding Common Stock. The securities exclude shares of Common Stock issuable upon conversion of shares of Non-Voting Common Stock in excess of the beneficial ownership limitation. Row 13 is based on 60,530,801 shares of Common Stock outstanding as of January 22, 2026, consisting of (i) 54,833,587 shares of Common Stock outstanding as of November 3, 2025, as reported in the Company's Form 10-Q filed on November 10, 2025, (ii) 42,208 shares of Common Stock underlying vested options held by Mr. Harwin and (iii) 5,655,006 shares of Common Stock underlying the 5,655,006 shares of Non-Voting Common Stock owned by Fund II, subject to 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. 0001830177 N Tomas Kiselak a AF N 2B 93374.00 5953653.00 93374.00 5953653.00 6047027.00 N 9.99 IN HC The securities include (a) 51,166 shares of Common Stock held directly by Mr. Kiselak, (b) 42,208 shares of Common Stock underlying vested options held by Mr. Kiselak* and (c) Fund II's direct holdings of (i) 298,647 shares of Common Stock and (ii) 5,655,066 shares of Common Stock issuable upon conversion of 5,655,066 shares of Non-Voting Common Stock, the conversion of which is subject to a beneficial ownership limitation of 9.99% of the outstanding Common Stock. The securities exclude shares of Common Stock issuable upon conversion of shares of Non-Voting Common Stock in excess of the beneficial ownership limitation. Row 13 is based on 60,530,801 shares of Common Stock outstanding as of January 22, 2026, consisting of (i) 54,833,587 shares of Common Stock outstanding as of November 3, 2025, as reported in the Company's Form 10-Q filed on November 10, 2025, (ii) 42,208 shares of Common Stock underlying vested options held by Mr. Kiselak and (iii) 5,655,006 shares of Common Stock underlying the 5,655,006 shares of Non-Voting Common Stock owned by Fund II, subject to 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. Common Stock, $0.00001 par value Apogee Therapeutics, Inc. 221 Crescent Street Building 17, Suite 102b Waltham MA 02453 This Amendment No. 4 amends and supplements the statement on Schedule 13D originally filed with the Securities and Exchange Commission (the "SEC") on July 21, 2023, Amendment No. 1 filed on January 31, 2024, Amendment No. 2 filed on April 1, 2024, and Amendment No. 3 filed on October 14, 2025 (as amended, the "Statement" or the "Schedule 13D") by the Reporting Persons with respect to the Common Stock of the Company. Unless otherwise defined herein, capitalized terms used in this Amendment No. 4 shall have the meanings ascribed to them in the Statement. Unless amended or supplemented below, the information in the Statement remains unchanged. The information in rows 11 and 13 of each of the cover pages (including the explanatory note in the "Comments") of this Amendment No. 4 is incorporated by reference herein. The information in rows 7 through 10 of each of the cover pages of this Amendment No. 4 is incorporated by reference herein. In the aggregate, the Reporting Persons have voting and dispositive power over 6,031,979 shares of Common Stock, which is comprised of the following: (i) 298,647 shares of Common Stock held by Fund II; (ii) 5,546,584 shares of Common Stock issuable upon conversion of 5,546,584 shares of Non-Voting Common Stock, held by Fund II, reflecting the beneficial ownership limitation of 9.99% of the outstanding Common Stock; (iii) 51,166 shares of Common Stock held by Mr. Harwin; (iv) 42,208 shares of Common Stock underlying vested options held by Mr. Harwin; (v) 51,166 shares of Common Stock held by Mr. Kiselak; and (vi) 42,208 shares of Common Stock underlying vested options held by Mr. Kiselak. In total, the Fund II currently owns 6,743,321 shares of Non-Voting Common Stock. Item 5(c) of the Schedule 13D is hereby amended and supplemented as follows: On January 22, 2026, Fund II sold in a block trade a total of 1,750,000 shares of Common Stock at a price of $76.30 per share. Company Stock Options On June 17, 2025, in their respective capacities as members of the Company's board of directors, Mr. Harwin and Mr. Kiselak were each granted stock options by the Company representing the right to purchase 14,461 shares of Common Stock. The options will vest on the one-year anniversary of the grant date, subject to Mr. Harwin and Mr. Kiselak's continued service to the Company on such vesting date. Under Mr. Harwin's and Mr. Kiselak's respective arrangements with Fairmount Funds Management, Mr. Harwin and Mr. Kiselak hold the options for one or more Fairmount Funds and are obligated to turn over to Fairmount Funds Management any net cash or stock received from the option for the benefit of such Fairmount Fund. Mr. Harwin and Mr. Kiselak therefore each disclaim beneficial ownership of their respective options and underlying common stock. 99.1 Joint Filing Agreement (incorporated by reference to Exhibit 99.1 to the Schedule 13D filed with the SEC on October 14, 2025) Fairmount Funds Management LLC /s/ Peter Harwin Peter Harwin, Managing Member 01/22/2026 /s/ Tomas Kiselak Tomas Kiselak, Managing Member 01/22/2026 Fairmount Healthcare Fund II L.P. /s/ Peter Harwin Peter Harwin, Managing Member 01/22/2026 /s/ Tomas Kiselak Tomas Kiselak, Managing Member 01/22/2026 Peter Evan Harwin /s/ Peter Harwin Peter Harwin 01/22/2026 Tomas Kiselak /s/ Tomas Kiselak Tomas Kiselak 01/22/2026