X0609 4 2026-08-24 0 0001728117 Gossamer Bio, Inc. GOSS 0001857256 Peterson Caryn false 3115 MERRYFIELD ROW, SUITE 120 SAN DIEGO CA 92121 0 1 0 0 Chief Development Officer 0 Stock Option (Right to Buy) 0.175 2026-08-24 4 A 0 5800051 0 A 2036-08-23 Common Stock 5800051 5800051 D 50% of the total number of shares subject to the option will vest upon FDA approval of seralutinib, and 1/24th of the remaining 50% of the total number of shares subject to the option will vest on the last day of each one-month period after such FDA approval, in each case subject to the Reporting Person's continuous service to the Issuer on each such vesting date. To the extent FDA approval of seralutinib does not occur on or prior to the date that is two years following the grant date of the option, 1/24th of the total number of shares subject to the option will vest on the last day of each one-month period following the date that is two years following the grant date of the option, subject to the Reporting Person's continuous service to the Issuer on each such vesting date. /s/ Jeff Boerneke, Attorney-in-Fact 2026-08-26