Sutro Biopharma Officer Nets 37,500 RSUs; 13,417 Shares Withheld for Taxes

Rhea-AI Filing Summary

Hans-Peter Gerber, Chief Scientific Officer of Sutro Biopharma, acquired equity and vested awards on 09/18/2025. The Form 4 shows 37,500 restricted stock units (RSUs) were recorded as acquired and will settle into common stock; each RSU converts to one share on settlement. Following the transactions, Mr. Gerber beneficially owned 75,000 shares of common stock. Additionally, the issuer withheld 13,417 shares

Positive

• 37,500 RSUs reported as acquired, reflecting compensation vesting that increases the officer's stake
• Beneficial ownership rose to 75,000 shares, providing increased alignment with shareholder interests
• Clear disclosure of tax withholding (13,417 shares) indicating proper remittance handling rather than a market sale

Negative

• 13,417 shares withheld reduced the net shares received by the officer, though this was for tax obligations

Insights

Securities Analyst

TL;DR: Officer received RSU vesting and net-share withholding; ownership increased to 75,000 shares, withholding satisfied tax obligations.

The filing documents routine insider vesting activity rather than open-market trades. The reported 37,500 RSUs converting to shares increases the officer's beneficial ownership to 75,000, which is a straightforward compensation-related equity grant vesting event. The 13,417 shares

Corporate Governance Expert

TL;DR: Governance disclosure is complete for a standard RSU vesting and withholding; no irregularities appear in the Form 4.

The Form 4 clearly identifies the reporting person as the Chief Scientific Officer and discloses both the RSU vesting (Code M) and the withholding (Code F). It includes vesting schedule details (annual 1/4th starting 09/18/2024) and confirms withheld shares were remitted for taxes. The signature line shows an attorney-in-fact filed on behalf of the officer. This meets disclosure expectations for related-party compensation events under Section 16.

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^*

Gerber Hans-Peter

(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)

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

3. Date of Earliest Transaction (Month/Day/Year)
09/18/2025

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	09/18/2025		M		37,500	A	$0	68,249	D
Common Stock	09/18/2025		F		13,417(1)	D	$0.9	54,832	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)	09/18/2025		M			37,500	(3)	09/18/2027	Common Stock	37,500	$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 RSU award vests annually as to 1/4th of the total award beginning on September 18, 2024, subject to the reporting person's continued service to the Issuer on each vesting date.

	/s/ David Pauling as attorney-in-fact for Hans-Peter Gerber	09/22/2025
	** 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).
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.

FAQ

What did Hans-Peter Gerber report on the Form 4 for STRO?

The Form 4 reports the acquisition/settlement of 37,500 RSUs on 09/18/2025 and withholding of 13,417 shares for tax obligations, resulting in 75,000 shares beneficially owned.

Were any shares sold by the reporting person in this filing?

No. The filing states the 13,417 shares were withheld to satisfy tax withholding related to net settlement and does not represent a sale by the reporting person.

What is the vesting schedule for the RSU award disclosed?

The RSU award vests annually as to 1/4th of the total award beginning on 09/18/2024, subject to continued service.

How many shares will each RSU convert into?

Each RSU represents a contingent right to receive one share of Sutro Biopharma common stock upon settlement.

Who filed the Form 4 on behalf of Hans-Peter Gerber?

The Form 4 was signed and filed by David Pauling as attorney-in-fact for Hans-Peter Gerber on 09/22/2025.