Sutro Biopharma (STRO) CEO reports RSU conversion and 282-share tax withholding

Rhea-AI Filing Summary

SUTRO BIOPHARMA, INC. director and Chief Executive Officer Jane Chung reported equity award activity involving restricted stock units and common stock. On March 4, 2026, 788 restricted stock units were exercised or converted into 788 shares of common stock at a stated price of $0.00 per share, reflecting settlement of previously granted RSUs.

On the same date, 282 shares of common stock were withheld at a price of $21.31 per share to satisfy income tax withholding and remittance obligations related to the net settlement of the RSUs, and the footnote clarifies this does not represent a sale by the reporting person. After these transactions, Jane Chung directly owned 21,285 shares of Sutro Biopharma common stock.

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)
03/04/2026

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	03/04/2026		M		788	A	$0	21,567	D
Common Stock	03/04/2026		F		282(1)	D	$21.31	21,285	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)	03/04/2026		M			788	(3)	03/04/2026	Common Stock	788	$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 1/4 of the total award annually, with the first tranche vested on March 4, 2023, subject to continued service through each vesting date.

	/s/ David Pauling as attorney-in-fact	03/06/2026
	** 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 March 4, 2026?

Jane Chung reported the net settlement of restricted stock units into 788 common shares and the withholding of 282 shares for taxes. These transactions reflect equity award vesting and tax withholding rather than open-market buying or selling.

How many Sutro Biopharma (STRO) shares did Jane Chung acquire from RSUs?

She acquired 788 shares of Sutro Biopharma common stock through the exercise or conversion of 788 restricted stock units. Each RSU represents a contingent right to receive one share of common stock upon settlement, as described in the filing footnotes.

Why were 282 shares of STRO common stock withheld from Jane Chung?

The company withheld 282 shares of common stock at $21.31 per share to cover income tax withholding and remittance obligations associated with the RSU settlement. The filing states this does not represent a sale by the reporting person.

How many Sutro Biopharma (STRO) shares does Jane Chung own after these transactions?

Following the reported RSU conversion and tax withholding, Jane Chung directly owned 21,285 shares of Sutro Biopharma common stock. This figure reflects her direct ownership after the March 4, 2026 transactions disclosed in the Form 4.

How do the STRO RSUs reported by Jane Chung vest over time?

The RSUs vest as to one-quarter of the total award annually, with the first tranche vesting on March 4, 2023. Continued service through each vesting date is required, according to the vesting schedule described in the Form 4 footnotes.

What does each Sutro Biopharma (STRO) RSU reported by Jane Chung represent?

Each restricted stock unit reported represents a contingent right to receive one share of Sutro Biopharma common stock upon settlement. This means vested RSUs convert into an equal number of common shares when they settle, as outlined in the filing.