GOSS

-- -- --

From December 31,2022 to December 31,2023 Issuance of common stock and warrants in connection with a private offering, net of offering costs of $10,779 Vesting of restricted stock Issuance of common stock pursuant to Employee Stock Purchase Plan Issuance of common stock for restricted stock units vested

From June 30, 2023 to September 30, 2023 Issuance of common stock and accompanying warrants in connection with a private offering, net of offering costs of $10,779 Issuance of common stock pursuant to Employee Stock Purchase Plan

From December 31, 2022 to March 31, 2023 Issuance of common stock pursuant to Employee Stock Purchase Plan Issuance of common stock for restricted stock units vested Vesting of restricted stock

From December 31, 2021 to December 31, 2022 Issuance of common stock in connection with a private offering, net of offering costs of $184 Issuance of common stock for restricted stock units vested Issuance of common stock pursuant to Employee Stock Purchase Plan Vesting of restricted stock Exercise of stock options

From June 30, 2022 to September 30, 2022 Vesting of restricted stock Exercise of stock options Issuance of common stock pursuant to Employee Stock Purchase Plan Issuance of common stock in connection with a private offering, net of offering costs of $184 Issuance of common stock for restricted stock units vested

From March 31, 2022 to June 30, 2022 Vesting of restricted stock Exercise of stock options Issuance of common stock for restricted stock units vested

From December 31, 2021 to March 31, 2022 Vesting of restricted stock Exercise of stock options Issuance of common stock pursuant to Employee Stock Purchase Plan Issuance of common stock for restricted stock units vested

From December 31, 2020 to December 31, 2021 Vesting of restricted stock Exercise of stock options Issuance of common stock pursuant to Employee Stock Purchase Plan Issuance of common stock for restricted stock units vested

From June 30, 2021 to September 30, 2021 Vesting of restricted stock Exercise of stock options Issuance of common stock pursuant to Employee Stock Purchase Plan

From March 31, 2021 to June 30, 2021 Vesting of restricted stock Exercise of stock options Issuance of common stock for restricted stock units vested

From December 31, 2020 To March 31, 2021 Vesting of restricted stock Exercise of stock options Issuance of common stock pursuant to Employee Stock Purchase Plan Issuance of common stock for restricted stock units vested

From December 31, 2019 to December 31, 2020 Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs Vesting of restricted stock Exercise of stock options Issuance of common stock pursuant to Employee Stock Purchase Plan

From June 30,2020 to September 30,2020 Vesting of restricted stock Exercise of stock options Issuance of common stock pursuant to Employee Stock Purchase Plan

From March 31, 2020 to June 30, 2020 Issuance of common stock in connection with public offering,net of underwriting discounts,commissions,and offering costs Vesting of restricted stock Exercise of stock options

On May 21, 2020, Gossamer Bio, Inc. (the “Company”) completed the public offering of 9,433,963 shares (the “Shares”) of common stock, par value $0.0001 per share, of the Company (the “Common Stock”) at a public offering price of $13.25 per share (the “Common Stock Offering”).

From December 31, 2019 to March 31, 2020 Vesting of restricted stock Exercise of stock options Issuance of common stock pursuant to Employee Stock Purchase Plan

from December 31, 2018 to December 31, 2019 Issuance of common stock in connection with a public offering,net of underwriting discounts,commissions,and offering costs Conversion of convertible preferred stock into common stock Vesting of restricted stock Exercise of stock options

from June 30, 2019 to September 30, 2019 Vesting of restricted stock Exercise of stock options

from March 31, 2019 to June 30,2019 Vesting of restricted stock Exercise of stock options

from December 31, 2018 to March 31, 2019 Conversion of convertible preferred stock into common stock Issuance of common stock in connection with a public offering, net of underwriting discounts, commissions, and offering costs Vesting of restricted stock Stock-based compensation

In January 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Incentive Award Plan (the “2019 Plan”). The 2019 Plan became effective on February 6, 2019, the day prior to the effectiveness of the registration statement filed in connection with the IPO. Under the 2019 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units, and other stock or cash-based awards to individuals who are then employees, officers, directors or consultants of the Company, and employees and consultants of the Company’s subsidiaries. A total of 5,750,000 shares of common stock were approved to be initially reserved for issuance under the 2019 Plan. The number of shares that remain available for issuance under the 2017 Plan as of the effective date of the 2019 Plan and shares subject to outstanding awards under the 2017 Plan as of the effective date of the 2019 Plan that are subsequently canceled, forfeited or repurchased by the Company will be added to the shares reserved under the 2019 Plan.

1.Common stock offered 17,250,000 shares 2.The number of shares of our common stock to be outstanding after this offering set forth above is based on 46,026,910 shares of our common stock outstanding as of September 30, 2018 3. A 20,612-for-one stock split of our common stock effected in January 2018 4. A one-for-4.5 reverse stock split of our common stock, which we effected on January 23, 2019

from December 31, 2017 to December 31, 2018 Issuance of Series A preferred stock for cash, net of $0.4 million in offering costs Issuance of stock for acquisition Issuance of Series A preferred stock to convert debt and accrued interest Issuance of Series B preferred stock for cash, net of $0.5 million in offering costs Vesting of restricted stock Incremental vesting conditions place on previously issued common shares