X0609 4 2026-08-24 0 0001728117 Gossamer Bio, Inc. GOSS 0001740847 Giraudo Bryan false 3115 MERRYFIELD ROW, SUITE 120 SAN DIEGO CA 92121 0 1 0 0 COO/CFO 0 Pre-Funded Warrant (Right to Buy) 0.0001 2026-08-24 4 A 0 25 999.999 A 2026-08-24 Series A-1 Preferred Stock 25 25 I By Family Trust Stock Option (Right to Buy) 0.175 2026-08-24 4 A 0 5800051 0 A 2036-08-23 Common Stock 5800051 5800051 D Each share of Series A-1 non-voting convertible preferred stock is convertible automatically upon receipt of stockholder approval under applicable Nasdaq rules and regulations in connection with the Issuer's private placement pursuant to which the Pre-Funded Warrants were issued ("Stockholder Approval") into a number of shares of the Issuer's common stock equal to $1,000 divided by $0.14, pursuant to the terms of the Series A-1 Certificate of Designation and subject to applicable beneficial ownership limitations. The Pre-Funded Warrant has no expiration date and is exercisable immediately. Prior to the Issuer obtaining Stockholder Approval, the Pre-Funded Warrants are only exercisable for shares of Series A-1 non-voting convertible preferred stock. Following the Issuer's receipt of Stockholder Approval, the Pre-Funded Warrants are only exercisable for shares of the Issuer's common stock. 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