Sutro Biopharma (STRO) GC reports new RSUs, options and tax share withholdings

Rhea-AI Filing Summary

SUTRO BIOPHARMA, INC. Chief Administrative Officer and General Counsel David Pauling reported multiple equity transactions. He acquired common stock through the vesting and settlement of restricted stock units (RSUs) and received new awards of 4,200 RSUs and stock options for 33,600 shares. Some common shares (970 and 551) were withheld at prices of $20.55 and $20.47 to satisfy tax obligations in connection with RSU settlements, which the company notes do not represent market sales by Pauling.

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)
03/01/2026

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	03/01/2026		M		500	A	$0	7,673	D
Common Stock	03/01/2026		M		842	A	$0	8,515	D
Common Stock	03/01/2026		F		551(1)	D	$20.47	7,964	D
Common Stock	03/02/2026		M		2,356	A	$0	10,320	D
Common Stock	03/02/2026		F		970(1)	D	$20.55	9,350	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 Units (RSUs)	(2)	03/01/2026		M			500	(3)	03/01/2027	Common Stock	500	$0	500	D
Restricted Stock Units (RSUs)	(2)	03/01/2026		M			842	(4)	03/01/2028	Common Stock	842	$0	1,686	D
Restricted Stock Units (RSUs)	(2)	03/02/2026		M			2,356	(5)	03/02/2029	Common Stock	2,356	$0	7,069	D
Restricted Stock Units (RSUs)	(2)	03/02/2026		A		4,200		(6)	03/01/2030	Common Stock	4,200	$0	4,200	D
Stock Option (right to buy)	$20.55	03/02/2026		A		33,600		(7)	03/02/2036	Common Stock	33,600	$0	33,600	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 RSUs; 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 1, 2024, subject to continued service through each vesting date.

4. The RSUs vested or vest as to 1/4 of the total award annually, with the first tranche vested on March 1, 2025, subject to continued service through each vesting date.

5. The RSUs vested or vest as to 1/4 of the total award annually, with the first tranche vested on March 2, 2026, subject to continued service through each vesting date.

6. The RSUs shall vest as to 1/4 of the total award annually, with the first tranche vesting on March 1, 2027, subject to continued service through each vesting date.

7. 1/48 of the total option award shall vest monthly, subject to the reporting person's continued service to the Issuer on each vesting date, with the first tranche vesting on April 1, 2026.

Remarks:

Effective as of 12:01 a.m. Eastern time on December 3, 2025, pursuant to a Certificate of Amendment to the Issuer's Restated Certificate of Incorporation previously approved by the Issuer's stockholders, and filed with the Delaware Secretary of State on December 2, 2025, the Issuer's Common Stock, par value $0.001 per share, underwent a 1-for-10 reverse stock split (the "Reverse Stock Split"). All amounts, including all dollar values, set forth herein have been adjusted to reflect the Reverse Stock Split.

	/s/ David Pauling	03/03/2026
	** Signature of Reporting Person	Date
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FAQ

What insider transactions did STRO executive David Pauling report on this Form 4?

David Pauling reported RSU settlements into common stock, a new grant of 4,200 restricted stock units, and stock options for 33,600 shares. He also reported share withholdings used to cover tax obligations related to these equity awards, rather than open-market stock sales.

How many restricted stock units did STRO’s David Pauling receive and how do they vest?

David Pauling received a grant of 4,200 restricted stock units. Footnotes state various RSU awards vest in four annual installments, with first tranches on March 1, 2024, March 1, 2025, March 2, 2026, or March 1, 2027, subject to continued service with Sutro Biopharma.

What stock option award did STRO grant to David Pauling and what is its vesting schedule?

David Pauling was granted stock options covering 33,600 shares. According to the disclosure, 1/48 of the total option award vests monthly, subject to his continued service, with the first tranche vesting on April 1, 2026, spreading vesting over four years of employment.

Were any of David Pauling’s STRO share dispositions open-market sales?

The filing shows dispositions coded as “F,” representing shares withheld to satisfy income tax withholding obligations. Footnotes explain 970 and 551 common shares were withheld for tax remittance from RSU settlements and that these amounts do not represent sales by the reporting person.

How did RSU settlements affect David Pauling’s STRO common stock holdings?

RSU conversions on March 1 and March 2, 2026 delivered several blocks of common stock, including 2,356, 500, and 842 shares. These increased his direct holdings, while a portion of the shares was simultaneously withheld to cover tax liabilities associated with the RSU net settlements.

What does each RSU reported by STRO’s David Pauling represent?

Each restricted stock unit represents a contingent right to receive one share of Sutro Biopharma common stock upon settlement. Vesting of these RSUs occurs over time, generally in four annual installments, contingent on David Pauling’s continued service through each specified vesting date.