Quanterix (QTRX) CEO Form 4 shows tax withholding of 1,242 shares

Rhea-AI Filing Summary

Quanterix Corp reported an insider equity transaction by its President & CEO and Director on 12/15/2025. The filing shows that 1,242 shares of common stock were withheld by Quanterix solely to cover tax obligations that arose when 3,722 restricted stock units (RSUs) vested. This is recorded as a disposition at a price of $7.41 per share for reporting purposes.

Following this tax withholding event, the reporting person beneficially owned 508,704 shares of Quanterix common stock, which includes 212,123 RSUs. The transaction was filed as a Form 4 for a single reporting person in their roles as both Director and President & CEO.

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^*

Toloue Masoud

(Last) (First) (Middle)

C/O QUANTERIX CORPORATION

900 MIDDLESEX TURNPIKE

(Street)

BILLERICA MA 01821

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Quanterix Corp [ QTRX ]

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

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	President & CEO

3. Date of Earliest Transaction (Month/Day/Year)
12/15/2025

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	12/15/2025		F		1,242(1)	D	$7.41	508,704(2)	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. Shares withheld by Quanterix Corporation solely to cover tax obligations upon vesting of 3,722 restricted stock units (RSUs).

2. Includes 212,123 RSUs

Remarks:

	/s/ Bonnie McManus, Attorney-in-Fact	12/18/2025
	** 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 insider transaction did Quanterix Corp (QTRX) report in this Form 4?

The report shows that 1,242 shares of Quanterix common stock were withheld on 12/15/2025 to cover tax obligations when 3,722 RSUs vested for the company’s President & CEO and Director.

Who is the reporting person in the Quanterix Corp (QTRX) Form 4 filing?

The reporting person is a Director and also serves as President & CEO of Quanterix Corp, as indicated in the relationship section of the filing.

How many Quanterix (QTRX) shares does the insider own after this transaction?

After the reported transaction, the insider beneficially owned 508,704 shares of Quanterix common stock, which includes 212,123 restricted stock units (RSUs).

What was the price used for the Quanterix (QTRX) tax withholding shares?

The 1,242 shares withheld to cover taxes were reported at a price of $7.41 per share in the Form 4.

Was this Quanterix (QTRX) insider transaction a sale on the open market?

No. The explanation states that the 1,242 shares were withheld by Quanterix Corporation solely to cover tax obligations upon vesting of 3,722 RSUs, rather than being an open-market sale.

What type of securities are involved in this Quanterix (QTRX) Form 4?

The filing involves common stock and underlying restricted stock units (RSUs) of Quanterix Corp, with shares withheld to satisfy tax obligations when the RSUs vested.