Sec Form 4 Filing - Aranda Richard @ Gossamer Bio, Inc. - 2023-05-05

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Aranda Richard 2. Issuer Name and Ticker or Trading Symbol Gossamer Bio, Inc. [ GOSS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Medical Officer (Last) (First) (Middle) 3013 SCIENCE PARK ROAD 3. Date of Earliest Transaction (MM/DD/YY) 05/05/2023 (Street) SAN DIEGO, CA92121 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Stock Option (Right to Buy) $ 22.1 05/05/2023 D 45,000 ( 1 ) 03/25/2029 Common Stock 45,000 ( 2 ) 0 D Stock Option (Right to Buy) $ 16.4 05/05/2023 D 13,750 ( 3 ) 12/23/2029 Common Stock 13,750 ( 4 ) 0 D Stock Option (Right to Buy) $ 14.55 05/05/2023 D 34,175 ( 5 ) 02/14/2030 Common Stock 34,175 ( 6 ) 0 D Stock Option (Right to Buy) $ 9.79 05/05/2023 D 60,000 ( 7 ) 02/25/2031 Common Stock 60,000 ( 8 ) 0 D Stock Option (Right to Buy) $ 8.47 05/05/2023 D 30,000 ( 9 ) 06/21/2031 Common Stock 30,000 ( 10 ) 0 D Stock Option (Right to Buy) $ 11.94 05/05/2023 D 190,000 ( 11 ) 01/05/2032 Common Stock 190,000 ( 12 ) 0 D Stock Option (Right to Buy) $ 1.36 ( 13 ) 05/05/2023 A 30,000 ( 1 ) 03/25/2029 Common Stock 30,000 ( 2 ) 30,000 D Stock Option (Right to Buy) $ 1.36 ( 13 ) 05/05/2023 A 9,167 ( 3 ) 12/23/2029 Common Stock 9,167 ( 4 ) 9,167 D Stock Option (Right to Buy) $ 1.36 ( 13 ) 05/05/2023 A 22,784 ( 5 ) 02/14/2030 Common Stock 22,784 ( 6 ) 22,784 D Stock Option (Right to Buy) $ 1.36 ( 13 ) 05/05/2023 A 40,000 ( 7 ) 02/25/2031 Common Stock 40,000 ( 8 ) 40,000 D Stock Option (Right to Buy) $ 1.36 ( 13 ) 05/05/2023 A 20,000 ( 9 ) 06/21/2031 Common Stock 20,000 ( 10 ) 20,000 D Stock Option (Right to Buy) $ 1.36 ( 13 ) 05/05/2023 A 126,667 ( 11 ) 01/05/2032 Common Stock 126,667 ( 12 ) 126,667 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Aranda Richard 3013 SCIENCE PARK ROAD SAN DIEGO, CA92121 Chief Medical Officer Signatures /s/ Jeff Boerneke, Attorney-in-Fact 05/09/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The shares subject to the option are fully vested. ( 2 )On May 5, 2023, the Issuer canceled an option granted on March 25, 2019. In exchange for the canceled option, the reporting person received 30,000 options to purchase common stock having a lower exercise price with the same vesting terms. ( 3 )25% of the total number of shares subject to the option vested on December 23, 2020 and 1/48th of the total number of shares subject to the option vest on the last day of each one-month period thereafter, subject to the Reporting Person's continuous service to the Issuer on each such vesting date. ( 4 )On May 5, 2023, the Issuer canceled an option granted on December 23, 2019. In exchange for the canceled option, the reporting person received 9,167 options to purchase common stock having a lower exercise price with the same vesting terms. ( 5 )25% of the total number of shares subject to the option vested on February 14, 2021 and 1/48th of the total number of shares subject to the option vest on the last day of each one-month period thereafter, subject to the Reporting Person's continuous service to the Issuer on each such vesting date. ( 6 )On May 5, 2023, the Issuer canceled an option granted on February 14, 2020. In exchange for the canceled option, the reporting person received 22,784 options to purchase common stock having a lower exercise price with the same vesting terms. ( 7 )25% of the total number of shares subject to the option vested on February 25, 2022 and 1/48th of the total number of shares subject to the option vest on the last day of each one-month period thereafter, subject to the Reporting Person's continuous service to the Issuer on each such vesting date. ( 8 )On May 5, 2023, the Issuer canceled an option granted on February 25, 2021. In exchange for the canceled option, the reporting person received 40,000 options to purchase common stock having a lower exercise price with the same vesting terms. ( 9 )25% of the total number of shares subject to the option vested on June 21, 2022 and 1/48th of the total number of shares subject to the option vest on the last day of each one-month period thereafter, subject to the Reporting Person's continuous service to the Issuer on each such vesting date. ( 10 )On May 5, 2023, the Issuer canceled an option granted on June 21, 2021. In exchange for the canceled option, the reporting person received 20,000 options to purchase common stock having a lower exercise price with the same vesting terms. ( 11 )One-third of the total number of shares subject to the option vested on January 6, 2023 and 1/36th of the total number of shares subject to the option vest on the last day of each one-month period thereafter, subject to the Reporting Person's continuous service to the Issuer on each such vesting date. ( 12 )On May 5, 2023, the Issuer canceled an option granted on January 6, 2022. In exchange for the canceled option, the reporting person received 126,667 options to purchase common stock having a lower exercise price with the same vesting terms. ( 13 )The exercise price of the option is $1.36 per share, representing the fair market value per share of the Issuer's common stock on the date of grant; provided that in the event the option is exercised prior to May 5, 2024, or the Reporting Person's employment terminates prior to May 5, 2024 other than due to death, disability or circumstances giving rise to severance under the Reporting Person's employment agreement, the exercise price will be increased to the exercise price of the cancelled option in exchange for which this option was granted.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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