Sutro Biopharma (STRO) GC exercises RSUs as shares withheld for taxes

Rhea-AI Filing Summary

SUTRO BIOPHARMA, INC. executive David Pauling, Chief Administrative Officer and General Counsel, reported equity transactions tied to restricted stock units on March 4, 2026. He exercised 675 RSUs, each converting into one share of common stock, and received 675 shares at a stated price of $0.00 per share.

To cover income tax withholding on this vesting, 277 common shares were withheld by the company at $21.31 per share, which the footnote clarifies does not represent a sale by Pauling. After these transactions, he directly owned 9,748 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^*

Pauling David

(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 Admin. Ofcr. & GC

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		675	A	$0	10,025	D
Common Stock	03/04/2026		F		277(1)	D	$21.31	9,748	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			675	(3)	03/04/2026	Common Stock	675	$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	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 report for David Pauling on March 4, 2026?

On March 4, 2026, David Pauling exercised 675 restricted stock units into 675 shares of Sutro Biopharma common stock at a stated price of $0.00 per share. The company then withheld 277 of those shares to satisfy related income tax obligations.

How many Sutro Biopharma (STRO) shares does David Pauling own after this Form 4?

After the March 4, 2026 transactions, David Pauling directly owns 9,748 shares of Sutro Biopharma common stock. This figure reflects the RSU conversion and the 277 shares withheld by the company to cover income tax withholding on the vested restricted stock units.

Were any of David Pauling’s STRO transactions market sales of stock?

No, the filing states that 277 shares were withheld by Sutro Biopharma to satisfy income tax withholding and remittance obligations for RSU settlement. A footnote explicitly clarifies this withholding does not represent a sale by David Pauling on the open market or to third parties.

What do the RSUs in David Pauling’s STRO Form 4 represent?

Each restricted stock unit represents a contingent right to receive one share of Sutro Biopharma common stock upon settlement. The RSUs vest in four equal annual installments, with the first tranche vesting on March 4, 2023, subject to continued service through each vesting date.

How do David Pauling’s RSUs in STRO vest over time?

The RSUs vest over four years, with one-quarter of the total award vesting annually. According to the disclosure, the first 25% vested on March 4, 2023, and additional tranches vest on subsequent anniversaries, provided David Pauling continues his service through each vesting date.