# EDGAR Filing Document

**Accession Number:** 0001728117
**File Stem:** 0001857256-26-000004
**Filing Date:** 2026-3
**Character Count:** 10464
**Document Hash:** 6b9030e9d37e1db0ae4b15ea59f4d48a
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001857256-26-000004.hdr.sgml**: 20260320

**ACCESSION NUMBER**: 0001857256-26-000004

**CONFORMED SUBMISSION TYPE**: 4

**PUBLIC DOCUMENT COUNT**: 1

**CONFORMED PERIOD OF REPORT**: 20260319

**FILED AS OF DATE**: 20260320

**DATE AS OF CHANGE**: 20260320

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** Peterson Caryn
- **CENTRAL INDEX KEY:** 0001857256

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 4
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-38796
- **FILM NUMBER:** 26778479

**MAIL ADDRESS:**
- **STREET 1:** 3013 SCIENCE PARK ROAD
- **CITY:** SAN DIEGO
- **STATE:** CA
- **ZIP:** 92121
**ISSUER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Gossamer Bio, Inc.
- **CENTRAL INDEX KEY:** 0001728117
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 475461709
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**BUSINESS ADDRESS:**
- **STREET 1:** 3115 MERRYFIELD ROW
- **STREET 2:** SUITE 120
- **CITY:** SAN DIEGO
- **STATE:** CA
- **ZIP:** 92121
- **BUSINESS PHONE:** (858) 684-1300

**MAIL ADDRESS:**
- **STREET 1:** 3115 MERRYFIELD ROW
- **STREET 2:** SUITE 120
- **CITY:** SAN DIEGO
- **STATE:** CA
- **ZIP:** 92121

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## FORM 4

### STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

[ ] 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**<sup>*</sup><br>Peterson Caryn<br><sub>(Last) (First) (Middle)</sub><br>3115 MERRYFIELD ROW, SUITE 120<br><sub>(Street)</sub><br>SAN DIEGO, CA 92121<br><sub>(City) (State) (Zip)</sub> | **3. Date of Earliest Transaction (Month/Day/Year)**<br>2026-03-19 | **5. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[ ] Director [ ] 10% Owner<br>[X] Officer (give title below) [ ] Other (specify below)<br>_EVP, Regulatory Affairs_ |
| **2. Issuer Name and Ticker or Trading Symbol**<br>Gossamer Bio, Inc. [ GOSS ] | **4. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[X] Form filed by One Reporting Person<br>[ ] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | 3. Transaction Code (V) | 3. Transaction Code (V) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | Code | V | Amount | (A) or (D) | Price | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
|  |  |  |  |  |  |  |  |  |  |  |

---

## Table II - Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | 4. Transaction Code (V) | 4. Transaction Code (V) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 6. Date Exercisable and Expiration Date | 6. Date Exercisable and Expiration Date | 7. Title and Amount of Underlying Securities | 7. Title and Amount of Underlying Securities | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | Code | V | (A) | (D) | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| Stock Option (Right to Buy) | $2.88 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 506250 | <sup>(2)</sup> | 2036-01-01 | Common Stock | 506250 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $1.13 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 440000 | <sup>(2)</sup> | 2035-03-03 | Common Stock | 440000 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $0.97 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 375000 | <sup>(2)</sup> | 2034-01-01 | Common Stock | 375000 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $0.838 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 125000 | <sup>(2)</sup> | 2033-11-19 | Common Stock | 125000 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $1.21 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 157500 | <sup>(2)</sup> | 2033-03-19 | Common Stock | 157500 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $2.16 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 157500 | <sup>(2)</sup> | 2032-12-06 | Common Stock | 157500 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $1.36 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 126667 | <sup>(2)</sup> | 2032-01-05 | Common Stock | 126667 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $1.36 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 21167 | <sup>(2)</sup> | 2031-04-16 | Common Stock | 21167 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $1.36 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 18834 | <sup>(2)</sup> | 2031-02-25 | Common Stock | 18834 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $1.36 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 22784 | <sup>(2)</sup> | 2030-02-14 | Common Stock | 22784 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $1.36 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 9167 | <sup>(2)</sup> | 2029-12-23 | Common Stock | 9167 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $1.36 | 2026-03-19 |  | D<sup>(1)</sup> |  |  | 32334 | <sup>(2)</sup> | 2029-03-25 | Common Stock | 32334 | <sup>(1)</sup> | 0 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 506250 |  | <sup>(2)</sup> | 2036-01-01 | Common Stock | 506250 | <sup>(1)</sup> | 506250 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 440000 |  | <sup>(2)</sup> | 2035-03-03 | Common Stock | 440000 | <sup>(1)</sup> | 440000 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 375000 |  | <sup>(2)</sup> | 2034-01-01 | Common Stock | 375000 | <sup>(1)</sup> | 375000 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 125000 |  | <sup>(2)</sup> | 2033-11-19 | Common Stock | 125000 | <sup>(1)</sup> | 125000 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 157500 |  | <sup>(2)</sup> | 2023-03-19 | Common Stock | 157500 | <sup>(1)</sup> | 157500 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 157500 |  | <sup>(2)</sup> | 2032-12-06 | Common Stock | 157500 | <sup>(1)</sup> | 157500 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 126667 |  | <sup>(2)</sup> | 2032-01-05 | Common Stock | 126667 | <sup>(1)</sup> | 126667 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 21167 |  | <sup>(2)</sup> | 2031-04-16 | Common Stock | 21167 | <sup>(1)</sup> | 21167 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 18834 |  | <sup>(2)</sup> | 2031-02-25 | Common Stock | 18834 | <sup>(1)</sup> | 18834 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 22784 |  | <sup>(2)</sup> | 2030-02-14 | Common Stock | 22784 | <sup>(1)</sup> | 22784 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 9167 |  | <sup>(2)</sup> | 2029-12-23 | Common Stock | 9167 | <sup>(1)</sup> | 9167 | D |  |
| Stock Option (Right to Buy) | $0.45 | 2026-03-19 |  | A<sup>(1)</sup> |  | 32334 |  | <sup>(2)</sup> | 2029-03-25 | Common Stock | 32334 | <sup>(1)</sup> | 32334 | D |  |

---

### Footnotes:

(1) Effective as of March 19, 2026 (the "Repricing Date"), the Issuer approved a one-time repricing of certain outstanding stock options (the "Repriced Options") granted under the Issuer's 2019 Incentive Award Plan (the "2019 Plan"), which reduced the per share exercise price of each Repriced Option to $0.45 (the "Option Repricing"). Except as modified by the Option Repricing, all other terms and conditions of the Repriced Options, including, without limitation, any provisions with respect to vesting and term of the Repriced Options, remain in full force and effect.

(2) This stock option award was issued pursuant to the 2019 Plan and becomes exercisable in accordance with the vesting schedule specified in the award agreement and as previously reported on applicable Form 4, subject to the Reporting Person's continued service with the Issuer as of the applicable vesting date.

**Signature:** /s/ Jeff Boerneke, Attorney-in-Fact  
**Date:** 2026-03-20

### Remarks:

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.**