Spero Therapeutics (SPRO) COO auto-sells 18,652 shares to cover RSU taxes

Rhea-AI Filing Summary

Spero Therapeutics Chief Operating Officer Timothy Keutzer reported an automatic sale of common stock tied to tax obligations. On 02/06/2026, 18,652 shares of common stock were sold at $2.36 per share to cover tax withholding arising from restricted stock unit (RSU) vesting.

After this transaction, Keutzer beneficially owned 742,506 shares of Spero Therapeutics common stock in direct form. The filing explains that the sale was a mandatory "sell to cover" transaction to fund taxes and was not a discretionary trade by the executive.

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^*

Keutzer Timothy

(Last) (First) (Middle)

C/O SPERO THERAPEUTICS, INC.

675 MASSACHUSETTS AVENUE, 14TH FLOOR

(Street)

CAMBRIDGE MA 02139

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Spero Therapeutics, Inc. [ SPRO ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Operating Officer

3. Date of Earliest Transaction (Month/Day/Year)
02/06/2026

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	02/06/2026		S(1)		18,652(1)	D	$2.36	742,506	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

Explanation of Responses:

1. Represents shares required to be sold by the Reporting Person to cover tax withholding obligations in connection with the vesting of RSUs. The sale occurred automatically to satisfy the tax withholding obligations to be funded by a "sell to cover" transaction and does not represent a discretionary trade by the Reporting Person.

	/s/ Maegan Deare, Attorney-in-Fact for Timothy Keutzer	02/09/2026
	** 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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** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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FAQ

What insider transaction did SPRO Chief Operating Officer Timothy Keutzer report?

Timothy Keutzer reported an automatic sale of 18,652 shares of Spero Therapeutics common stock. The shares were sold at $2.36 each to cover tax withholding obligations triggered by vesting RSUs, rather than representing a discretionary open-market sale by the executive.

How many SPRO shares does Timothy Keutzer hold after this Form 4 transaction?

Following the reported transaction, Timothy Keutzer beneficially owned 742,506 shares of Spero Therapeutics common stock. These shares are reported as directly held, indicating continued substantial equity exposure to the company after the tax-related sell-to-cover transaction disclosed in the Form 4.

Was the SPRO insider sale by Timothy Keutzer a discretionary trade?

No, the sale was not discretionary. The footnote states the 18,652 shares were sold automatically under a “sell to cover” arrangement to satisfy tax withholding obligations from vesting RSUs, meaning the transaction was driven by tax requirements rather than an elective share sale.

At what price were the SPRO shares sold in Timothy Keutzer’s Form 4 filing?

The 18,652 Spero Therapeutics common shares were sold at $2.36 per share. This price reflects the execution level for the tax-related sell-to-cover transaction that funded Keutzer’s withholding obligations upon the vesting of restricted stock units granted by the company.

What is the significance of the RSU-related tax sale disclosed by SPRO’s COO?

The filing shows shares were sold solely to cover taxes on vesting RSUs, a common administrative step in equity compensation. It indicates the COO continues to hold 742,506 shares directly, so the transaction does not reflect a broad reduction of his overall ownership position.

What role does Timothy Keutzer hold at Spero Therapeutics (SPRO)?

Timothy Keutzer is reported as the Chief Operating Officer of Spero Therapeutics. His status as an officer triggers Section 16 reporting duties, so transactions in the company’s common stock, including this RSU-related sell-to-cover sale, must be disclosed on Form 4 filings with the SEC.