[Form 4] Quanterix Corporation Insider Trading Activity

Rhea-AI Filing Summary

Form 4 for Quanterix Corp (QTRX) shows Toloue Masoud, President & CEO and a director, reported transactions dated 08/31/2025. The filing records a disposition of 254 shares of common stock at $4.55 per share. The disposition reflects shares withheld by the company to cover tax obligations upon the vesting of 761 restricted stock units (RSUs). After the reported transaction, Masoud beneficially owns 514,434 shares, which include 228,052 RSUs. The form was signed by an attorney-in-fact on 09/03/2025.

Positive

• Significant insider ownership: Toloue Masoud beneficially owns 514,434 shares, indicating strong alignment with shareholders
• Routine compensation mechanics: Disposition reflects tax withholding on RSU vesting, a standard, non-adversarial transaction

Negative

• Share withholding reduces immediately tradable shares: 254 shares were disposed of to cover taxes upon vesting

Insights

Corporate Governance Expert

TL;DR: Routine vesting and tax-withholding; insider retains large equity stake.

The filing documents a common post-vesting administrative action where the company withheld 254 shares to satisfy tax obligations on 761 vested RSUs. This is a standard compensation settlement rather than a purposeful liquidity-driven sale by management. The report confirms the CEO remains a significant shareholder with 514,434 shares, including 228,052 RSUs, maintaining alignment with long-term shareholder interests. No governance red flags or unusual transfer patterns are evident from the data provided.

Financial Analyst

TL;DR: Small share disposition; overall insider ownership remains substantial.

The disposition of 254 shares at $4.55 appears tied solely to tax withholding on vested RSUs, reducing the CEO’s immediate free shares but leaving aggregate beneficial ownership intact at 514,434 shares. The large number of outstanding RSUs (228,052) signals continued potential future dilution as they vest and convert, but the filing itself indicates routine compensation mechanics rather than a material change in ownership or corporate outlook.

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

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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)
08/31/2025

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	08/31/2025		F		254(1)	D	$4.55	514,434(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 761 RSUs.

2. Includes 228,052 restricted stock units.

Remarks:

	/s/ Brian Keane, as Attorney-in-Fact	09/03/2025
	** 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 transaction did Toloue Masoud (QTRX) report on Form 4?

The filing reports a disposition of 254 shares of Quanterix common stock on 08/31/2025 at $4.55 per share.

Why were shares disposed of in this Form 4 for QTRX?

The filing states the shares were withheld by Quanterix to cover tax obligations upon the vesting of 761 RSUs.

How many shares does the reporting person own after the transaction?

After the reported transaction, Toloue Masoud beneficially owns 514,434 shares, which include 228,052 restricted stock units.

What is Toloue Masoud’s role at Quanterix (QTRX)?

The filer is listed as President & CEO and a director of Quanterix Corporation.

When was the Form 4 signed and by whom?

The form was signed by Brian Keane, as Attorney-in-Fact on 09/03/2025.