X0609 4 2026-06-09 0001798749 Jade Biosciences, Inc. JBIO 0001802528 Fairmount Funds Management LLC false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false 0001769651 Fairmount Healthcare Fund II L.P. false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false 0002042283 Fairmount Healthcare Co-Invest IV L.P. false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false 0001830177 Kiselak Tomas false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false 0001663607 Harwin Peter Evan false 200 BARR HARBOR DRIVE, SUITE 400 WEST CONSHOHOCKEN PA 19428 true false true false false Stock Option (Right to Buy) 15.22 2026-06-09 4 A false 34843 0 A 2036-06-08 Common Stock 34843 34843 D This option represents a right to purchase shares of the Issuer's common stock, which vests in full on the earlier of (i) June 9, 2027 or (ii) the date of the next annual meeting of the Issuer's stockholders, in each case, subject to Tomas Kiselak's continued service to the Issuer. Fairmount Funds Management LLC ("Fairmount") is the investment manager for Fairmount Healthcare Fund II LP ("Fund II") and Fairmount Healthcare Co-Invest IV L.P. ("Co-Invest"). Peter Harwin and Tomas Kiselak are the managers of Fairmount. Under Mr. Kiselak's arrangement with Fairmount, Mr. Kiselak holds the option 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. Fairmount, Mr. Harwin, and Mr. Kiselak disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein. Fairmount, Fairmount Healthcare Fund II L.P. and Fairmount Healthcare Co-Invest IV L.P. may each be deemed a director by deputization of the Issuer by virtue of the fact that Tomas Kiselak serves on the board of directors of the Issuer and is also a Managing Member of Fairmount. /s/ Tomas Kiselak, Managing Member of Fairmount Funds Management LLC 2026-06-11 /s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Fund II L.P. 2026-06-11 /s/ Tomas Kiselak, Managing Member of Fairmount Healthcare Co-Invest IV L.P. 2026-06-11 /s/ Tomas Kiselak 2026-06-11 /s/ Peter Harwin 2026-06-11