Sutro Biopharma (STRO) Insider Report: RSU Award and Tax Withholding

Rhea-AI Filing Summary

Barbara Leyman, Chief Business Officer of Sutro Biopharma, reported changes in her holdings on Form 4. She received 25,000 restricted stock units (RSUs) on 07/08/2025 that vest in four equal annual installments beginning 07/08/2025, and those RSUs convert to common stock upon settlement. Following the reported transactions, she beneficially owns 75,000 RSUs. Separately, 8,944 shares of common stock were withheld by the issuer to satisfy tax withholding related to a net settlement of RSUs; this withholding is not a sale by the reporting person. After the withholding and the reported acquisition, she directly beneficially owns 16,056 shares of common stock.

Positive

• 25,000 RSU grant increases the reporting person's long-term equity stake and aligns incentives with shareholders
• RSUs vest over four years, supporting retention and performance alignment
• Withholding to satisfy taxes is disclosed and is not a sale, indicating routine compensation mechanics

Negative

• 8,944 shares withheld reduced the reporting person's immediately held common stock to 16,056 shares, lowering liquid ownership
• RSUs are time-vested and not immediately marketable, so the increase in equity is not immediately liquid or voting power-enhancing

Insights

Securities Analyst

TL;DR: Officer received a sizable RSU award while the company withheld shares for taxes; overall ownership increases in RSUs but liquid common shares declined.

The report shows a compensation-related equity grant (25,000 RSUs) that increases the reporting person’s long-term equity exposure to the company, with vesting over four years starting 07/08/2025. The withholding of 8,944 shares to cover taxes reduced the reporting person’s immediately held common shares to 16,056, but this is a non-dispositive tax action rather than a market sale. For investors, the key point is that management’s equity stake via RSUs increased, aligning executive incentives with long-term performance, while short-term liquid share count decreased due to withholding.

Corporate Governance Specialist

TL;DR: Routine equity compensation disclosure; no signs of opportunistic selling or governance red flags.

The Form 4 reflects routine executive compensation and tax withholding mechanics. The grant of 25,000 RSUs is typical for senior officers and vests over multiple years, which supports retention and alignment. The withheld 8,944 shares were used solely to satisfy tax obligations on net-settled RSUs and are explicitly not a sale. There is no indication of abnormal trading, insider divestiture, or change in control activity in this filing.

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

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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^*

Leyman Barbara

(Last) (First) (Middle)

C/O SUTRO BIOPHARMA, INC.

111 OYSTER POINT BOULEVARD

(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)

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

3. Date of Earliest Transaction (Month/Day/Year)
07/08/2025

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	07/08/2025		M		25,000	A	$0	25,000	D
Common Stock	07/08/2025		F		8,944(1)	D	$0.78	16,056	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)	07/08/2025		M			25,000	(3)	07/08/2028	Common Stock	25,000	$0	75,000	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 vest as to 1/4th of the total award annually beginning on July 8, 2025, subject to the reporting person's continued service to the Issuer through each vesting date.

	/s/ David Pauling as attorney-in-fact for Barbara Leyman	08/26/2025
	** 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).
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FAQ

What transactions did Barbara Leyman report on Sutro Biopharma (STRO) Form 4?

She reported a grant of 25,000 RSUs on 07/08/2025 and the withholding of 8,944 common shares to satisfy tax obligations from RSU settlement.

How many RSUs and shares does Barbara Leyman beneficially own after the reported transactions?

Following the transactions, she beneficially owns 75,000 RSUs and 16,056 shares of common stock.

When do the RSUs granted to Barbara Leyman begin to vest?

The RSUs vest in four equal annual installments beginning on July 8, 2025.

Was the withholding of 8,944 shares a sale by the reporting person?

No. The Form 4 states the shares were withheld by the issuer to satisfy income tax withholding in connection with net settlement and do not represent a sale.

Does this Form 4 indicate any unusual insider selling or governance concerns for STRO?

No. The filing reflects routine equity compensation and tax withholding mechanics; there is no indication of opportunistic selling or other governance red flags.