Quanterix CEO (QTRX) withholds 254 shares; now holds 511,442

Quanterix (QTRX) reported an insider tax-withholding event by its President & CEO and Director.

Rhea-AI Filing Summary

Quanterix (QTRX) reported an insider tax-withholding event by its President & CEO and Director. On October 31, 2025, 254 shares of common stock were withheld at $5.34 to cover taxes upon vesting of 761 RSUs.

After this transaction, the insider beneficially owns 511,442 shares, which includes 219,086 RSUs. The filing reflects routine administration of equity compensation rather than an open‑market sale.

Insider Trade Summary

Exercise Price or Tax Liability: 254 shares

Exercise Price or Tax Liability 1 txn

Insider Toloue Masoud

Role President & CEO

Type	Security	Shares	Price	Value
Exercise Price or Tax Liability	Common Stock	254	$5.34	$1K

Holdings After Transaction: Common Stock — 511,442 shares (Direct)

Footnotes (2)

1. F1. Shares withheld by Quanterix Corporation solely to cover tax obligations upon vesting of 761 restricted stock units (RSUs).
2. F2. Includes 219,086 RSUs

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What did Quanterix (QTRX) disclose in this Form 4?

An insider tax-withholding transaction: 254 shares were withheld at $5.34 to cover taxes on 761 RSUs that vested on October 31, 2025.

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

The individual is both a Director and Officer (President & CEO) of Quanterix.

How many shares does the insider own after the transaction?

The insider beneficially owns 511,442 shares following the transaction, including 219,086 RSUs.

Was this an open-market sale of Quanterix shares?

No. The code F indicates shares were withheld by the issuer to satisfy tax obligations upon RSU vesting.

What is the price associated with the withheld shares?

The tax-withheld shares are reported at $5.34 per share.

What triggered the withholding of shares?

Vesting of 761 RSUs led to withholding 254 shares to cover taxes, as noted in the explanation of responses.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 11/05/2025 - 01:12 PM Learn about SEC filing dates

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^*

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)
10/31/2025

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	10/31/2025		F		254(1)	D	$5.34	511,442(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 761 restricted stock units (RSUs).

2. Includes 219,086 RSUs

Remarks:

	/s/ Brian Keane, as Attorney-in-Fact	11/04/2025
	** 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.