Spero Therapeutics (SPRO) officer sells shares for RSU tax obligations

Rhea-AI Filing Summary

Spero Therapeutics, Inc. officer Rajavelu Esther reported an automatic sale of common stock tied to tax withholding on vested restricted stock units. On May 4, 2026, 25,240 shares were sold at $2.51 per share to fund a “sell to cover” tax obligation rather than a discretionary trade. After this transaction, Esther directly owned 986,851 shares of Spero Therapeutics common stock.

Insider Trade Summary

Net Seller: 25,240 shares ($63,352)

Net Sell 1 txn

Insider Rajavelu Esther

Role See Remarks

Sold 25,240 shs ($63K)

Type	Security	Shares	Price	Value
Sale	Common Stock	25,240	$2.51	$63K

Holdings After Transaction: Common Stock — 986,851 shares (Direct, null)

Footnotes (1)

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Key Figures

Shares sold: 25,240 shares Sale price: $2.51 per share Shares held after transaction: 986,851 shares

3 metrics

Shares sold 25,240 shares Automatic sale on May 4, 2026 to cover RSU tax withholding

Sale price $2.51 per share Price for Spero Therapeutics common stock sold in Form 4 transaction

Shares held after transaction 986,851 shares Direct ownership by Rajavelu Esther following the May 4, 2026 sale

Key Terms

RSUs, sell to cover, tax withholding obligations

3 terms

RSUs financial

"in connection with the vesting of RSUs. The sale occurred automatically"

RSUs, or restricted stock units, are a form of company shares given to employees as part of their compensation. They are typically awarded with certain restrictions, such as a waiting period before they can be fully owned or sold, similar to earning a gift that becomes fully yours over time. For investors, RSUs can impact a company's stock offerings and reflect how much the company relies on stock-based incentives to attract and retain talent.

sell to cover financial

"to be funded by a "sell to cover" transaction and does not represent"

Sell to cover is when a person who receives company stock through options or awards sells just enough shares immediately to pay required taxes, exercise costs, or fees, keeping the rest. Think of it like cashing part of a bonus to cover the tax bill so you can keep the remainder. For investors, it can create predictable small selling pressure and slightly change the number of shares actually held by insiders without increasing long‑term dilution.

tax withholding obligations financial

"shares required to be sold by the Reporting Person to cover tax withholding obligations in connection"

Form 4 Insider Transactions: What Each Field Means →

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
Estimated average burden
hours per response:			0.5

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^*

Rajavelu Esther

(Last) (First) (Middle)

C/O SPERO THERAPEUTICS, INC.

675 MASSACHUSETTS AVENUE, 14TH FLOOR

(Street)

CAMBRIDGE MASSACHUSETTS 02139

(City) (State) (Zip)

UNITED STATES

(Country)

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)
	See Remarks

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
05/04/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

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	05/04/2026		S(1)		25,240(1)	D	$2.51	986,851	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.

Remarks:

Chief Executive Officer, Chief Financial Officer and Chief Business Officer

	/s/ Maegan Deare, Attorney-in-Fact for Esther Rajavelu	02/09/2026
	** 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.
* Form 4: SEC 1474 (03-26)

FAQ

What insider transaction did Spero Therapeutics (SPRO) report for Rajavelu Esther?

Spero Therapeutics reported that officer Rajavelu Esther sold 25,240 common shares. The shares were sold at $2.51 each to cover tax withholding obligations from vested RSUs through an automatic sell-to-cover transaction.

Was the SPRO insider sale by Rajavelu Esther a discretionary trade?

No, the sale was not discretionary. The footnote states the 25,240 shares were sold automatically to cover tax withholding obligations related to RSU vesting, executed as a predefined “sell to cover” transaction.

How many Spero Therapeutics (SPRO) shares does Rajavelu Esther hold after the sale?

Following the sale, Rajavelu Esther directly owns 986,851 Spero Therapeutics common shares. This indicates the transaction was small relative to the remaining holdings and primarily for tax withholding purposes on vested RSUs.

At what price were the Spero Therapeutics (SPRO) shares sold in this Form 4?

The 25,240 Spero Therapeutics common shares were sold at $2.51 per share. According to the footnote, this sale was executed automatically to cover tax withholding obligations arising from the vesting of restricted stock units.

What does “sell to cover” mean in the Spero Therapeutics (SPRO) Form 4 footnote?

“Sell to cover” means a portion of shares from vested RSUs are sold automatically to pay required tax withholding. In this case, 25,240 Spero Therapeutics shares were sold solely to satisfy those tax obligations, not as an elective market sale.