UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No.     )

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☐ Preliminary Proxy Statement

☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material under §240.14a-12

Gossamer Bio, Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

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☐ Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

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Important Notice Regarding the Availability of Proxy Materials for the Shareholder Meeting to be held on June 17, 2020 for Gossamer Bio, Inc.  This communication is not a form for voting and presents only an overview of the more complete proxy materials that are available to you on the Internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. To view the proxy materials, go to www.proxydocs.com/GOSS. To submit your proxy while visiting this site, you will need the 12 digit control number in the box below.  Under new United States Securities and Exchange Commission rules, proxy materials do not have to be delivered in paper. Proxy materials can be distributed by making them available on the Internet. We have chosen to use these procedures for our 2020 Annual Meeting and need YOUR participation.  If you want to receive a paper or e-mail copy of the proxy materials, you must request one. There is no charge to you for requesting a copy. In order to receive a paper package in time for this year’s annual meeting, please make this request on or before June 7, 2020. For a Convenient Way to VIEW Proxy Materials  – and –  VOTE Online go to: www.proxydocs.com/GOSS    You must use the 12 digit control number  located in the shaded gray box below. * If requesting material by e-mail, please send a blank e-mail with the 12 digit control number (located below) in the subject line. No other requests, instructions or other inquiries should be included with your e-mail requesting material.    Company Notice of Annual Meeting  Date:  June 17, 2020  Time:  9:00 a.m. (Pacific Time)  Place:  Annual Meeting to be held live via the Internet – please visit  www.proxydocs.com/GOSS for more details.    The purpose of the Annual Meeting is to take action on the following proposals:  The Board of Directors recommends that you vote “FOR” the following nominees for Director in Proposal 1.  1.  Election of Directors  Nominees  01 Joshua Bilenker, M.D.  02 Faheem Hasnain  The Board of Directors recommends that you vote “FOR” Proposal 2.  2. Ratification of the appointment of Ernst & Young LLP as our independent registered public accountants for the year ending December 31, 2020.  TO ATTEND the Annual Meeting of Gossamer Bio, Inc., please visit www.proxydocs.com/GOSS for virtual meeting registration  details. The control number located in the shaded gray box will be required to register.    INTERNET www.investorelections.com/GOSS    TELEPHONE (866) 648-8133    *E-MAIL paper@investorelections.com    ACCOUNT NO. SHARES