To the beneficial owners, or representatives acting on behalf of beneficial owners, of the following notes (the “Existing Convertible Notes”): 5.00% Convertible Senior Notes due 2027 (CUSIP: 38341P AA0) issued by Gossamer Bio, Inc.

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Gossamer Bio, Inc., a Delaware corporation (the “Offeror”), is undertaking certain transactions with respect to the Existing Convertible Notes (the “Exchange Offer and Consent Solicitation”), including (i) exchanging any and all of the above listed Existing Convertible Notes for a combination of: (a) the Offeror’s common stock, par value $0.0001 per share (the “Common Stock”), or, in lieu of issuing shares of Common Stock, prefunded warrants to purchase shares of Common Stock (the “Prefunded Warrants” and together with the Common Stock, the “Equity Securities”), (b) with respect to eligible holders, warrants to purchase shares of the Offeror’s Common Stock (the “Purchase Warrants”) and (c) new convertible debt securities to be issued by the Offeror (the “New Convertible Notes,” and together with the Equity Securities and Purchase Warrants, the “Offered Securities”), and (ii) soliciting consents from holders of the Existing Convertible Notes to adopt certain proposed amendments to the respective indenture under which the Existing Convertible Notes were issued.

If you are a beneficial owner, or a representative acting on behalf of a beneficial owner, of Existing Convertible Notes that is an Eligible Holder (as defined below), please complete the attached eligibility letter (the “Eligibility Letter”) and return it to D.F. King & Co. Inc. at the address set forth in the Eligibility Letter. If you are a beneficial owner of Existing Convertible Notes that is not an Eligible Holder, please do not take any action at this time.

An “Eligible Holder” is a beneficial owner that certifies that it is: a “Qualified Institutional Buyer,” as that term is defined in Rule 144A under the Securities Act of 1933, as amended (the “Securities Act”).