[Form 4] Sutro Biopharma, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Jane Chung, Chief Executive Officer and Director of Sutro Biopharma, Inc. (STRO), reported insider activity on Form 4 dated 08/26/2025 covering transactions with an earliest date of 08/09/2025. The filing shows the vesting of 18,750 restricted stock units (RSUs) that settled into 18,750 shares of common stock (transaction code M), increasing her beneficial ownership to 117,058 shares. The issuer withheld 6,708 shares

Positive

• CEO increased direct ownership to 117,058 shares following RSU settlement, aligning executive and shareholder interests
• Transaction is a routine RSU vesting and net settlement; withheld shares were used only for tax obligations and were not sold by the reporting person

Negative

• None.

Insights

Corporate Governance Expert

TL;DR: Routine executive award vesting with standard tax withholding; not a material governance event.

The Form 4 documents the scheduled vesting and net settlement of RSUs for the CEO, increasing direct holdings to 117,058 shares. The issuer withheld 6,708 shares to meet tax obligations, explicitly stated as not a sale by the reporting person. This is a customary equity compensation settlement and does not indicate a change in control, compensation policy, or an unusual liquidity event. For governance oversight, monitor future filings for any discretionary accelerated vesting or additional derivative transactions.

Securities Analyst

TL;DR: Executive received vested RSUs; share-withholding for taxes reduced issued shares but is routine and immaterial to valuation.

The vesting of 18,750 RSUs increases the CEO's direct stake to 117,058 shares, while 6,708 shares were withheld by the issuer to satisfy tax obligations at the reported $0.80 withholding price. This net-settlement reduces the number of new shares delivered but is a standard compensation practice and does not reflect open-market selling pressure. Absent other material transactions or disclosures, this filing is informational and unlikely to move investor valuation assumptions on its own.

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)
08/09/2025

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	08/09/2025		M		18,750	A	$0	117,058	D
Common Stock	08/09/2025		F		6,708(1)	D	$0.8	110,350	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)	08/09/2025		M			18,750	(3)	08/09/2025	Common Stock	18,750	$0	0	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 1/4th of the total award annually beginning on August 9, 2022, subject to the reporting person's provision of service to the issuer on each vesting date.

	/s/ David Pauling as attorney-in-fact for Jane Chung	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).
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FAQ

What did Jane Chung report on the Form 4 for STRO?

The filing reports the vesting and settlement of 18,750 RSUs into 18,750 shares and the withholding of 6,708 shares for tax purposes, resulting in 117,058 shares beneficially owned.

Did the Form 4 show any open-market sales by the CEO of STRO?

No. The 6,708 shares were withheld by the issuer to satisfy tax withholding and the filing explicitly states this does not represent a sale by the reporting person.

When did the reported transactions occur?

The earliest transaction date reported on the Form 4 is 08/09/2025 and the form was signed on 08/26/2025.

What is the significance of transaction codes M and F on this Form 4?

Code M denotes the vesting/settlement of RSUs into shares and Code F denotes a disposition of shares to satisfy tax withholding in connection with net settlement.

How were the RSUs scheduled to vest?

The RSUs vest with 1/4 of the total award annually beginning August 9, 2022, subject to the reporting person's continued service.