EXHIBIT 32.1

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350

AS ADOPTED PURSUANT TO SECTION 906

OF THE SARBANES-OXLEY ACT OF 2002

I, Faheem Hasnain, President and Chief Executive Officer of Gossamer Bio, Inc. (the “Company”), do hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that to the best of my knowledge:

•the accompanying Quarterly Report on Form 10-Q of the Company for the quarter ended June 30, 2024 (the “Report”), as filed with the Securities and Exchange Commission, fully complies with the requirements of Section 13(a) or Section 15(d), as applicable, of the Securities Exchange Act of 1934, as amended; and

•the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company for the periods presented therein.

Date: August 12, 2024

/s/ Faheem Hasnain

Faheem Hasnain

President and Chief Executive Officer

(Principal Executive Officer)