Sutro Biopharma (STRO) CEO receives RSU and option grants, shares withheld for taxes

Rhea-AI Filing Summary

Sutro Biopharma CEO Jane Chung reported multiple equity award and vesting transactions. She received a grant of 40,000 Restricted Stock Units (RSUs) and a stock option for 175,000 shares, both with service-based vesting schedules over time.

RSUs previously granted to her vested on March 1 and March 2, 2026, and were settled into common stock through several derivative exercises. In connection with these vestings, a total of 2,779 shares at $20.55 and 1,271 shares at $20.47 of common stock were withheld by the company to cover income tax obligations, which the footnotes state do not represent sales by the reporting person.

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)
03/01/2026

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	03/01/2026		M		688	A	$0	14,579	D
Common Stock	03/01/2026		M		2,500	A	$0	17,079	D
Common Stock	03/01/2026		F		1,271(1)	D	$20.47	15,808	D
Common Stock	03/02/2026		M		7,750	A	$0	23,558	D
Common Stock	03/02/2026		F		2,779(1)	D	$20.55	20,779	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 Units (RSUs)	(2)	03/01/2026		M			688	(3)	03/01/2027	Common Stock	688	$0	688	D
Restricted Stock Units (RSUs)	(2)	03/01/2026		M			2,500	(4)	03/01/2028	Common Stock	2,500	$0	5,000	D
Restricted Stock Units (RSUs)	(2)	03/02/2026		M			7,750	(5)	03/02/2029	Common Stock	7,750	$0	23,250	D
Restricted Stock Units (RSUs)	(2)	03/02/2026		A		40,000		(6)	03/01/2030	Common Stock	40,000	$0	40,000	D
Stock Option (right to buy)	$20.55	03/02/2026		A		175,000		(7)	03/02/2036	Common Stock	175,000	$0	175,000	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 restricted stock units; does not represent a sale by the reporting person.

2. Each RSU represents a contingent right to receive one (1) share of the Issuer's Common Stock upon settlement.

3. The RSUs vested or vest as to 1/4 of the total award annually, with the first tranche vested on March 1, 2024, subject to continued service through each vesting date.

4. The RSUs vested or vest as to 1/4 of the total award annually, with the first tranche vested on March 1, 2025, subject to continued service through each vesting date.

5. The RSUs vested or vest as to 1/4 of the total award annually, with the first tranche vested on March 2, 2026, subject to continued service through each vesting date.

6. The RSUs shall vest as to 1/4 of the total award annually, with the first tranche vesting on March 1, 2027, subject to continued service through each vesting date.

7. 1/48 of the total option award shall vest monthly, subject to the reporting person's continued service through each vesting date, with the first tranche vesting on April 1, 2026.

	/s/ David Pauling as attorney-in-fact	03/03/2026
	** 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 transactions did STRO CEO Jane Chung report on this Form 4?

Jane Chung reported RSU vesting, new RSU and option grants, and related tax withholding. Several RSU awards converted into common stock, while new grants of 40,000 RSUs and 175,000 stock options were awarded, all subject to continued service-based vesting over future dates.

How many RSUs were granted to STRO CEO Jane Chung in this filing?

She received a grant of 40,000 Restricted Stock Units. Each RSU represents a contingent right to one share of Sutro Biopharma common stock upon settlement, with the award vesting in four annual installments starting March 1, 2027, conditioned on continued employment service.

What stock options were awarded to STRO CEO Jane Chung?

She was granted a stock option covering 175,000 shares of common stock. According to the footnotes, one forty-eighth of this option vests monthly, beginning April 1, 2026, provided she continues serving the company through each applicable vesting date.

Were any of Jane Chung’s STRO share dispositions open-market sales?

The filing indicates no open-market sales. Shares labeled with transaction code F, totaling 2,779 and 1,271 shares, were withheld by Sutro Biopharma to satisfy income tax obligations on RSU settlements and, per the footnotes, do not represent sales by her.

How do the RSU awards for STRO’s CEO vest over time?

Each RSU award vests in four annual tranches of one quarter of the total award. Different grants start vesting on March 1, 2024, March 1, 2025, March 2, 2026, and March 1, 2027, all requiring Jane Chung’s continued service through each vesting date.

What happened when Jane Chung’s RSUs vested into STRO common stock?

When RSUs vested, they were settled into common stock through derivative exercises coded M. A portion of the resulting shares was withheld by the issuer to cover income tax liabilities, leaving the remainder as directly held common shares in her reported ownership.