[Form 4] Spero Therapeutics, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Timothy Keutzer, Chief Operating Officer of Spero Therapeutics (SPRO), reported a sale of company common stock on 08/28/2025. The filing shows 1,695 shares were sold at $1.97 per share under a "sell to cover" provision tied to RSU vesting granted on August 26, 2021, and the sale was executed to satisfy tax withholding obligations. After the transaction, the reporting person beneficially owned 739,744 shares directly. The Form 4 was signed by an attorney-in-fact on behalf of Mr. Keutzer on 09/02/2025.

Positive

• Reporting person retains substantial ownership: 739,744 shares beneficially owned following the transaction
• Transaction disclosed as routine: Sale executed to satisfy tax withholding from RSU vesting, per the filing

Negative

• Shares sold: 1,695 common shares sold at $1.97 per share on 08/28/2025

Insights

Financial Analyst

TL;DR: Routine insider sell-to-cover; small quantity sold relative to total holdings, so market impact is negligible.

The transaction is a standard sell-to-cover tied to RSU vesting rather than an opportunistic market sale, as the filer explicitly states it was to satisfy tax withholding obligations from RSUs granted in 2021. The amount sold (1,695 shares at $1.97) is immaterial relative to the remaining beneficial ownership (739,744 shares), indicating no meaningful change to insider alignment with shareholders. For investors, this transaction is disclosure-driven and does not signal a change in executive confidence based on the filing alone.

Corporate Governance Expert

TL;DR: Compliance-focused filing documents routine tax-withholding sale; governance processes appear followed.

The Form 4 records that the sell-to-cover occurred under terms of RSU agreements, which is a common mechanism to satisfy withholding without requiring a cash payment by the insider. The form identifies the reporting person as COO and shows the filing was completed by an attorney-in-fact, consistent with standard disclosure practices. There are no indications of policy breaches or atypical insider behavior in this report.

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

OMB APPROVAL

OMB Number:			3235-0287
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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)
08/28/2025

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	08/28/2025		S(1)		1,695(1)	D	$1.97	739,744	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. The reported transaction is a sale of common stock effected to cover tax withholding obligations pursuant to a "sell to cover" provision included in each RSU Agreement in connection with the vesting of restricted stock units ("RSUs") that were granted to the Reporting Person on August 26, 2021.

	/s/ Maegan Deare, Attorney-in-Fact for Timothy Keutzer	09/02/2025
	** 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).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What did the SPRO Form 4 filed for Timothy Keutzer report?

The Form 4 reports a sale of 1,695 shares at $1.97 on 08/28/2025 and shows 739,744 shares beneficially owned after the sale.

Why were shares sold according to the Form 4 for SPRO?

The filing states the sale was a "sell to cover" to satisfy tax withholding obligations related to restricted stock units granted on August 26, 2021.

What is Timothy Keutzer's role at Spero Therapeutics as shown on the Form 4?

The Form 4 identifies Timothy Keutzer as an Officer, specifically the Chief Operating Officer.

When was the Form 4 signed and by whom?

The Form 4 was signed on behalf of Timothy Keutzer by Maegan Deare, Attorney-in-Fact on 09/02/2025.

Does the Form 4 indicate any derivative transactions or other securities activity?

No. The filing lists only a non-derivative sale of common stock and contains no derivative transactions.