Item 5.03 Amendments to Articles of Incorporation or Bylaws; Change in Fiscal Year.
On August 24, 2026, in connection with the closing of its previously announced private placement, Gossamer Bio, Inc. (the "Company") amended its amended and restated certificate of incorporation by filing with the Secretary of State of the State of Delaware the previously disclosed Certificate of Designation of Preferences, Rights and Limitations of Series A-1 Convertible Preferred Stock of the Company (the "Series A-1 Certificate of Designation"). The description of the rights and preferences of the Series A-1 Convertible Preferred Stock in Item 1.01 of the Current Report on Form 8-K filed by the Company with the Securities and Exchange Commission on August 21, 2026 is incorporated herein by reference, and such description is qualified in its entirety by reference to the Series A-1 Certificate of Designation, which is filed hereto as Exhibit 3.1.