Gossamer Bio grants director option on 10,000 shares

The option's full vesting is conditional on Sandra Milligan continuing to serve on Gossamer Bio's board through the grant's first anniversary.

Available on EDGAR 09/25/2026 - 05:19 PM EDT Accepted by SEC EDGAR 09/25/2026 - 05:17 PM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

Gossamer Bio, Inc. director Sandra Milligan was granted a stock option covering 10,000 shares of common stock on September 23, 2026, with an exercise price of $10.99 per share. The reported post-grant position in this option was 10,000 underlying shares, and the option expires September 22, 2036. All shares subject to the option become fully vested and exercisable on the first anniversary of the grant, subject to Milligan's continued board service through that date. No Rule 10b5-1 plan is reported.

Insider Trade Summary

Grant/Award: 10,000 shares

Grant/Award 1 txn

Insider Milligan Sandra

Role Director

Type	Security	Shares	Price	Value
Grant/Award	Stock Option (Right to Buy) F1	10,000	$0.00	$0.00

Holdings After Transaction: Stock Option (Right to Buy) — 10,000 options (Direct)

Holdings Before and After: Stock Option (Right to Buy), 0 to 10,000 options (Direct)

Footnotes (1)

1. F1. The entire number of shares subject to this option becomes fully vested and exercisable on the first anniversary of the grant date, subject to the Reporting Person's continued service on the board of directors of the Issuer through such vesting date.

Key Figures

Shares subject to option: 10,000 shares Exercise price: $10.99 per share Grant date: September 23, 2026 +1 more

4 metrics

Shares subject to option 10,000 shares Grant on September 23, 2026

Exercise price $10.99 per share Stock option grant

Grant date September 23, 2026 Stock option

Expiration date September 22, 2036 Stock option

Key Terms

Stock Option (Right to Buy), exercise price, fully vested and exercisable, continued service

4 terms

Stock Option (Right to Buy) financial

"Stock Option (Right to Buy)"

exercise price financial

"conversion_or_exercise_price"

The exercise price is the fixed amount at which you can buy or sell an asset, like a stock, when using an options contract. It matters because it helps determine whether exercising the option will be profitable or not, depending on the current market price. Think of it as the set price you agree on today to buy or sell later.

fully vested and exercisable financial

"becomes fully vested and exercisable on the first anniversary"

continued service financial

"subject to the Reporting Person's continued service on the board"

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many GOSS shares does Sandra Milligan's option cover, and what is its exercise price?

Sandra Milligan's stock option covers 10,000 shares and has an exercise price of $10.99 per share.

Was Sandra Milligan's GOSS option grant made under a Rule 10b5-1 plan?

No Rule 10b5-1 plan is reported for Sandra Milligan's option grant.

AI-generated analysis. How Rhea-AI works. Not financial advice.

Form 4 Insider Transactions: What Each Field Means →

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SEC Form 4

FORM 4

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
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

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

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Milligan Sandra

(Last) (First) (Middle)

3115 MERRYFIELD ROW, SUITE 120

(Street)

SAN DIEGO CALIFORNIA 92121

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
Gossamer Bio, Inc. [ GOSS ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
	Officer (give title below)		Other (specify below)

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
09/23/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	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 (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	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 (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (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: 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)	$10.99	09/23/2026		A		10,000		(1)	09/22/2036	Common Stock	10,000	$0	10,000	D

Explanation of Responses:

1. The entire number of shares subject to this option becomes fully vested and exercisable on the first anniversary of the grant date, subject to the Reporting Person's continued service on the board of directors of the Issuer through such vesting date.

Remarks:

	/s/ Christian Waage, Attorney-in-Fact	09/25/2026
	** Signature of Reporting Person	Date
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).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)