Gossamer Bio, Inc.

From time to time, we may be involved in legal proceedings or subject to claims incident to the ordinary course of business. Regardless of the outcome, such proceedings or claims can have an adverse impact on us because of defense and settlement costs, diversion of resources and other factors, and there can be no assurances that favorable outcomes will be obtained. We are currently subject to the following legal proceeding:

Kinnamon vs. Gossamer Bio, Inc., et. al.

On March 31, 2026, Daniel Kinnamon, individually and on behalf of all others similarly situated, filed a putative class action lawsuit against the Company and certain of its executive officers and directors in the United States District Court for the Southern District of California (Case No. 3:26-cv-2016-CAB-AHG). The complaint was filed on behalf of all persons who purchased or otherwise acquired the Company’s securities between June 16, 2025 and February 20, 2026. The complaint alleges that the Company and certain of its executive officers and directors made false and/or misleading statements and failed to disclose material adverse facts about its business, operations and prospects in violation of Sections 10(b) (and Rule 10b-5 promulgated thereunder) and 20(a) of the Securities Exchange Act of 1934, as amended. The plaintiff seeks damages, interest, costs, attorneys’ fees, and other unspecified equitable relief. On May 4, 2026, the Court entered an order staying any answer or response to the complaint pending the appointment of a lead plaintiff and lead counsel. On July 7, 2026, the Court entered an order appointing Martin Meienhofer and his counsel—The Rosen Law Firm—as Lead Plaintiff and Lead Counsel, respectively. On August 10, 2026, Lead Plaintiff and additional named plaintiffs Mike Fleming and Peter Zech, or collectively, Plaintiffs, filed an amended complaint against the Company, Faheem Hasnain, and Bryan Giraudo (collectively, “Defendants”). On September 9, 2026, Defendants filed a motion to dismiss the amended complaint. On September 30, 2026, Plaintiffs filed a second amended complaint in lieu of filing an opposition to the motion to dismiss, and on October 5, 2026, the Court denied the pending motion to dismiss as moot in light of the filing of the second amended complaint. On October 30, 2026, Defendants filed a motion to dismiss the second amended complaint. Plaintiffs’ opposition is due by December 2, 2026, and Defendants’ reply is due by December 11, 2026. The Company intends to vigorously defend this matter. Given the uncertainty of litigation, the preliminary stage of the case, and the legal standards that must be met for, among other things, class certification and success on the merits, the Company cannot estimate the reasonably possible loss or range of loss that may result from this action.