Sutro Biopharma (STRO) CEO details RSU vesting and share withholding

Rhea-AI Filing Summary

Sutro Biopharma CEO and director Jane Chung reported the vesting and settlement of restricted stock units on 12/12/2025. She received 2,500 shares of common stock at an exercise price of $0, and 894 shares were withheld by the company at $8.015 per share to cover tax obligations, which the filing states does not represent a sale by her. Following these transactions, she directly owns 13,891 shares of common stock and 5,000 RSUs, each RSU representing the right to receive one share upon settlement. The award vests in annual quarters, with the first tranche having vested on December 1, 2024. All share and dollar amounts reflect a 1-for-10 reverse stock split of Sutro Biopharma common stock that became effective on December 3, 2025.

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

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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^*

Chung Jane

(Last) (First) (Middle)

C/O SUTRO BIOPHARMA, INC.

111 OYSTER POINT BLVD.

(Street)

SOUTH SAN FRANCISCO CA 94080

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
SUTRO BIOPHARMA, INC. [ STRO ]

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

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

3. Date of Earliest Transaction (Month/Day/Year)
12/12/2025

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

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

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

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
Common Stock	12/12/2025		M		2,500	A	$0	14,785	D
Common Stock	12/12/2025		F		894(1)	D	$8.015	13,891	D

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
Restricted Stock Unit (RSU)	(2)	12/12/2025		M			2,500	(3)	12/01/2027	Common Stock	2,500	$0	5,000	D

Explanation of Responses:

1. Represents the number of shares of Common Stock that have been withheld by the Issuer to satisfy its income tax withholding and remittance obligations in connection with the net settlement of RSUs; does not represent a sale by the reporting person.

2. Each RSU represents a contingent right to receive one share of the Issuer's Common Stock upon settlement.

3. The RSU award vested or vests as to 1/4th of the total award annually, subject to continued service through each vesting date, with the first tranche vested on December 1, 2024. The reported transaction represents the deferred vesting and settlement of a tranche of this award pursuant to the terms of the reporting person's award agreement with the Issuer.

Remarks:

Effective as of 12:01 a.m. Eastern time on December 3, 2025, pursuant to a Certificate of Amendment to the Issuer's Restated Certificate of Incorporation previously approved by the Issuer's stockholders, and filed with the Delaware Secretary of State on December 2, 2025, the Issuer's Common Stock, par value $0.001 per share, underwent a 1-for-10 reverse stock split (the "Reverse Stock Split"). All amounts, including all dollar values, set forth herein have been adjusted to reflect the Reverse Stock Split.

	/s/ David Pauling as attorney-in-fact for Jane Chung	12/16/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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FAQ

What insider share activity did Sutro Biopharma (STRO) report for Jane Chung?

The company reported that CEO Jane Chung had restricted stock units vest on 12/12/2025, resulting in the issuance of 2,500 shares of common stock and related tax withholding.

How many Sutro Biopharma (STRO) shares does CEO Jane Chung own after this transaction?

After the reported transactions, Jane Chung directly owns 13,891 shares of Sutro Biopharma common stock and holds 5,000 RSUs, each RSU being a right to receive one share upon settlement.

Were any of Jane Chungs Sutro Biopharma (STRO) shares sold in the market?

The filing states that 894 shares of common stock were withheld by the issuer to satisfy income tax withholding obligations in connection with RSU settlement and that this does not represent a sale by Jane Chung.

What price is associated with the Sutro Biopharma shares withheld for taxes?

The 894 shares of common stock withheld to cover tax obligations are reported at a price of $8.015 per share.

How do Jane Chungs restricted stock units (RSUs) in Sutro Biopharma vest?

The RSU award vests as to one quarter of the total award annually, subject to continued service on each vesting date, with the first tranche having vested on December 1, 2024.

What reverse stock split did Sutro Biopharma (STRO) implement before this insider transaction?

Sutro Biopharma implemented a 1-for-10 reverse stock split of its common stock effective on December 3, 2025, and all share and dollar amounts in the report are adjusted for this split.