Quanterix (QTRX) COO gains shares from RSU vesting as stock withheld for taxes

Rhea-AI Filing Summary

Quanterix Corp’s Chief Operating Officer Michael Francis Miller reported routine equity compensation activity. On March 15, 2026, multiple restricted stock unit awards converted into common stock, with derivative exercises totaling 1,558 shares according to the filing’s transaction summary.

To cover related tax obligations, 549 common shares were withheld at a price of $4.72 per share under code F transactions, which are tax-withholding dispositions rather than market sales. Following these transactions, Miller directly holds 31,271 shares of Quanterix common stock.

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^*

Miller Michael Francis

(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)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Operating Officer

3. Date of Earliest Transaction (Month/Day/Year)
03/15/2026

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	03/15/2026		M		81	A	(1)	30,343	D
Common Stock	03/15/2026		F		29	D	$4.72	30,314	D
Common Stock	03/15/2026		M		136	A	(1)	30,450	D
Common Stock	03/15/2026		F		48	D	$4.72	30,402	D
Common Stock	03/15/2026		M		135	A	(1)	30,537	D
Common Stock	03/15/2026		F		48	D	$4.72	30,489	D
Common Stock	03/15/2026		M		372	A	(1)	30,861	D
Common Stock	03/15/2026		F		131	D	$4.72	30,730	D
Common Stock	03/15/2026		M		834	A	(1)	31,564	D
Common Stock	03/15/2026		F		293	D	$4.72	31,271	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
Restricted Stock Unit	$0.00	03/15/2026		M			81	(2)	(2)	Common Stock	81	$0.00	922	D
Restricted Stock Unit	$0.00	03/15/2026		M			136	(3)	(3)	Common Stock	136	$0.00	1,661	D
Restricted Stock Unit	$0.00	03/15/2026		M			135	(4)	(4)	Common Stock	135	$0.00	3,116	D
Restricted Stock Unit	$0.00	03/15/2026		M			372	(5)	(5)	Common Stock	372	$0.00	9,689	D
Restricted Stock Unit	$0.00	03/15/2026		M			834	(6)	(6)	Common Stock	834	$0.00	8,855	D

Explanation of Responses:

1. Restricted stock units convert into common stock on a one-for-one basis.

2. On February 6, 2023, the reporting person was granted 3,929 restricted stock units, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the 15th day of each month thereafter.

3. On March 15, 2023, the reporting person was granted 6,566 restricted stock units, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the 15th day of each month thereafter.

4. On February 2, 2024, the reporting person was granted 6,494 restricted stock units, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the 15th day of each month thereafter.

5. On May 21, 2024, the reporting person was granted 17,878 restricted stock units, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the 15th day of each month thereafter.

6. On February 4, 2025, the reporting person was granted 40,036 restricted stock units, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the 15th day of each month thereafter.

Remarks:

	/s/ Bonnie McManus, Attorney-in-Fact	03/17/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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FAQ

What insider transactions did Quanterix (QTRX) report for its COO?

Quanterix reported that COO Michael Francis Miller had restricted stock units convert into common stock. On March 15, 2026, derivative exercises totaled 1,558 shares, with a portion of the resulting stock withheld to satisfy tax obligations, reflecting routine equity compensation activity.

How many Quanterix (QTRX) shares were exercised and withheld for taxes?

The filing shows 1,558 shares acquired through restricted stock unit exercises and 549 shares withheld for taxes. The tax-withholding dispositions occurred at a price of $4.72 per share and are labeled with transaction code F, indicating non-market, tax-related share transfers.

What is Michael Francis Miller’s Quanterix (QTRX) shareholding after these Form 4 transactions?

After the reported March 15, 2026 transactions, Michael Francis Miller directly owns 31,271 shares of Quanterix common stock. This figure comes from the total_shares_following_transaction line associated with his final non-derivative entry in the Form 4 insider trading report.

Were the Quanterix (QTRX) COO’s transactions open-market buys or sales?

No open-market buys or sales were reported. The Form 4 lists code M derivative exercises converting restricted stock units to common stock and code F tax-withholding dispositions. Code F indicates shares delivered to cover tax liabilities, not discretionary market sales or purchases.

What do the restricted stock unit grants mean for Quanterix (QTRX) COO compensation?

The grants represent stock-based compensation that vests over time. Footnotes describe several RSU awards from 2023 to 2025, each vesting 25% after one year and the remaining 75% in 36 monthly installments, aligning Miller’s compensation with Quanterix’s long-term performance.

How do the RSU vesting schedules for Quanterix (QTRX) COO work?

Each referenced RSU grant vests 25% on the first anniversary of its grant date, with the remaining 75% vesting in 36 equal monthly installments on the 15th of each month. This creates a gradual, time-based release of Quanterix equity to the COO as part of compensation.