Quanterix Insider Filing: Masoud Retains 513,192 Shares; RSUs Withheld for Taxes

Rhea-AI Filing Summary

Toloue Masoud, who serves as President & CEO and a director of Quanterix Corporation (QTRX), reported a sale of 1,242 shares of common stock at $4.97 per share. The filing states these shares were disposed (code F) and that 3,722 restricted stock units vested, with shares withheld solely to cover tax obligations related to that vesting. After the reported transaction Masoud is shown as beneficially owning 513,192 shares in total, which include 224,330 restricted stock units.

Insights

Securities Analyst

TL;DR: Small sale versus large overall holding; transaction reflects tax withholding on RSU vesting rather than a material disposition of stake.

Masoud sold 1,242 shares at $4.97, recorded under transaction code F, while 3,722 RSUs vested and shares were withheld to satisfy tax obligations. Total beneficial ownership remains 513,192 shares, including 224,330 RSUs, indicating continued substantial alignment with shareholders. The sale size is minor relative to total holdings and appears administrative in nature.

Corporate Governance Expert

TL;DR: Insider retained significant equity; the reported disposal appears driven by tax mechanics, not an exit signal.

The form identifies Masoud as both a director and the President & CEO and documents withholding of shares to cover taxes on vested RSUs. Retaining over half a million shares with a large RSU component suggests continued executive ownership. The disclosure is routine under Section 16 reporting for equity compensation events.

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).

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)
09/15/2025

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	09/15/2025		F		1,242(1)	D	$4.97	513,192(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 the vesting of 3,722 RSUs.

2. Includes 224,330 restricted stock units.

Remarks:

	/s/ Brian Keane, as Attorney-in-Fact	09/17/2025
	** 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 Toloue Masoud report in the Form 4 for QTRX?

The filing reports a sale of 1,242 shares at $4.97 and discloses withholding of shares to cover taxes on 3,722 vested RSUs; total beneficial ownership is 513,192 shares including 224,330 RSUs.

Why were shares withheld according to the Form 4?

The filing states shares were withheld solely to cover tax obligations arising from the vesting of restricted stock units.

What is the size of Masoud's holdings after the transaction?

After the reported transaction the filing shows Masoud as beneficially owning 513,192 shares in total, which includes 224,330 restricted stock units.

Does the Form 4 indicate a change in Masoud's role at Quanterix (QTRX)?

No. The filing lists Masoud as a Director and as the company's President & CEO; it does not report any change in his roles.

How many RSUs vested according to the filing?

The filing shows that 3,722 restricted stock units vested, with shares withheld to satisfy related tax obligations.