X0609 4 2026-09-23 0 0001728117 Gossamer Bio, Inc. GOSS 0001859810 Milligan Sandra false 3115 MERRYFIELD ROW, SUITE 120 SAN DIEGO CA 92121 1 0 0 0 0 Stock Option (Right to Buy) 10.99 2026-09-23 4 A 0 10000 0 A 2036-09-22 Common Stock 10000 10000 D The entire number of shares subject to this option becomes fully vested and exercisable on the first anniversary of the grant date, subject to the Reporting Person's continued service on the board of directors of the Issuer through such vesting date. /s/ Christian Waage, Attorney-in-Fact 2026-09-25