[Form 4] Quanterix Corp Insider Trading Activity

Rhea-AI Filing Summary

Quanterix Corp (QTRX) disclosed an insider transaction by its President & CEO and Director on 10/15/2025. The filing shows 1,242 shares of common stock were withheld (code F) at $5.78 per share to cover taxes upon the vesting of 3,722 RSUs.

Following this tax-withholding transaction, the reporting person beneficially owns 511,696 shares, which includes 219,847 RSUs. This is an administrative, non‑open market event tied to equity award vesting.

Insider Trade Summary

1 transaction reported

Mixed 1 txn

Insider Toloue Masoud

Role President & CEO

Type	Security	Shares	Price	Value
Tax Withholding	Common Stock	1,242	$5.78	$7K

Holdings After Transaction: Common Stock — 511,696 shares (Direct)

Footnotes (1)

1. Shares withheld by Quanterix Corporation solely to cover tax obligations upon vesting of 3,722 restricted stock units (RSUs). Includes 219,847 RSUs

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^*

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)
10/15/2025

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	10/15/2025		F		1,242(1)	D	$5.78	511,696(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 219,847 RSUs

Remarks:

	/s/ Brian Keane, as Attorney-in-Fact	10/17/2025
	** 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 Quanterix (QTRX) report in this Form 4?

The President & CEO and Director had 1,242 shares withheld (code F) at $5.78 on 10/15/2025 to cover taxes on vesting equity.

What triggered the share withholding for QTRX's insider?

Vesting of 3,722 RSUs led to shares being withheld to satisfy tax obligations.

How many shares does the insider own after the transaction?

Beneficial ownership is 511,696 shares, which includes 219,847 RSUs.

Was this an open-market buy or sell?

No. Code F indicates shares were withheld by the issuer solely to cover taxes upon RSU vesting.

Which roles does the reporting person hold at Quanterix (QTRX)?

The reporting person is President & CEO and a Director of Quanterix Corp.

What was the price used for the tax withholding?

The withholding was recorded at $5.78 per share.