Gossamer Bio, Inc.

Item 8.01 Other Events. As previously disclosed, on July 14, 2026, the stockholders of Gossamer Bio, Inc. (the “Company”) approved thirty alternate amendments to the Company’s Amended and Restated Certificate of Incorporation to effect a reverse stock split (the “Reverse Stock Split”) of the Company’s common stock, par value $0.0001 per share (the “Common Stock”), at one of thirty reverse stock split ratios, with the exact ratio to be determined by the board of directors of the Company (the “Board”), and a proportionate reduction in the number of authorized shares of Common Stock (and a corresponding decrease in the total number of authorized shares of capital stock) (the “Authorized Share Reduction”). On September 9, 2026, the Company announced that the Board has selected a 1-for-80 reverse stock split ratio. The Reverse Stock Split and Authorized Share Reduction are expected to become effective on September 10, 2026, at 11:59 p.m. Eastern Time (the “Effective Time”). Shares of Common Stock are expected to begin trading on a split-adjusted basis on the Nasdaq Global Select Market at market open on September 11, 2026 under the existing trading symbol “GOSS” and a new CUSIP number of 38341P 201. The Reverse Stock Split is intended to help the Company regain compliance with the minimum bid price requirement for continued listing on the Nasdaq Global Select Market. In connection with the Reverse Stock Split, every 80 shares of Common Stock issued and outstanding immediately prior to the Effective Time will be automatically reclassified and combined into 1 share of Common Stock. No fractional shares of Common Stock will be issued as a result of the Reverse Stock Split. Instead, the Company will issue to holders of record who are entitled to a fraction of a share as a result of the Reverse Stock Split, a fraction of a share of Common Stock as is necessary to round up to the nearest whole share. For shares held through The Depository Trust Company ("DTC"), fractions of shares will be issued as is necessary to round up to the nearest whole share at the DTC participant level. Brokers, banks or other nominees holding shares in "street name" will be instructed to effect the Reverse Stock Split for their beneficial holders; however, such brokers, banks or other nominees may apply their own specific procedures for processing the Reverse Stock Split. Upon the effectiveness of the Reverse Stock Split, the conversion rates of the Company’s outstanding convertible notes (including the 5.00% Convertible Senior Notes due 2027 and the 7.50% Convertible Senior Secured First Lien Notes due 2030), the number of shares of Common Stock issuable upon exercise of outstanding warrants and prefunded warrants and the exercise prices thereof, and the number of shares subject to outstanding equity awards under the Company’s equity incentive plans (and the applicable exercise prices thereof), will each be proportionately adjusted pursuant to their respective terms and as determined by the Board to reflect the 1-for-80 reverse stock split ratio. In addition, the number of shares reserved for future issuance under the Company's equity incentive plans will be proportionately reduced. In connection with the Authorized Share Reduction, the number of authorized shares of Common Stock will be reduced from 4,000,000,000 to 50,000,000, and the total number of authorized shares of capital stock will be correspondingly reduced from 4,070,000,000 to 120,000,000. A copy of the press release announcing the Reverse Stock Split and Authorized Share Reduction is attached hereto as Exhibit 99.1 and is incorporated herein by reference. * * * Note Regarding Forward-Looking Statements. The Company cautions you that statements contained in this report regarding matters that are not historical facts are forward-looking statements. These statements are based on the Company’s current beliefs and expectations. Such forward-looking statements include, but are not limited to, statements regarding: the expected timing and effectiveness of the Reverse Stock Split and Authorized Share Reduction, the anticipated adjustments to the Company’s outstanding convertible notes, warrants, prefunded warrants and equity awards, the anticipated impact of the Reverse Stock Split on the Company’s ability to regain compliance with the Nasdaq minimum bid price requirement and the other effects of the reverse stock split, including the expected issuance of additional fractional shares of common stock as is necessary to round up to the nearest whole share. The inclusion of forward-looking statements should not be regarded as a representation by Gossamer that any of its plans will be achieved. Actual results may differ from those set forth in this report due to the risks and uncertainties inherent in Gossamer’s business, including, without limitation: the Reverse Stock Split may not result in a sustained increase in the price of the Company’s Common Stock and may not satisfy the Nasdaq minimum bid price requirement; any delay in the planned reverse stock split; the reverse stock split may impact our results of operations, business operations and reputation as well as the trading prices and volatility of the common stock; unstable market and economic conditions and changes in healthcare legislation, tariffs and trade policies may adversely affect the Company’s business and financial condition and the broader economy and biotechnology industry; and other risks described in the Company’s filings with the Securities and Exchange Commission (“SEC”), including under the heading “Risk Factors” in the Company’s annual report on Form 10-K and any subsequent filings with the SEC. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof, and Gossamer undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995.