Quanterix (QTRX) COO Miller details PSUs, RSUs, options and shares in Form 3

Rhea-AI Filing Summary

Quanterix Corp Chief Operating Officer Michael Francis Miller filed an initial ownership report showing his equity-based holdings in the company. As of February 23, 2026, he holds 74,905 Performance Stock Units granted on February 15, 2026, which vest in four equal annual installments after meeting performance conditions under the 2026 Employee Equity Guidelines.

He also holds multiple Restricted Stock Unit awards, including 74,905 RSUs granted on February 15, 2026 that vest 25% per year for four years, plus earlier RSU grants from 2022–2025 with monthly vesting schedules after the first anniversary. In addition, he has several option grants to buy Common Stock at exercise prices between $8.4300 and $54.0400 per share, with expirations between July 28, 2031 and February 4, 2035, and directly owns 30,262 shares of Common Stock.

SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

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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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. Date of Event Requiring Statement (Month/Day/Year)
02/23/2026

3. Issuer Name and Ticker or Trading Symbol
Quanterix Corp [ QTRX ]

4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

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

5. 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 Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock	30,262	D

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Performance Stock Unit	(1)	12/31/2026	Common Stock	74,905	$0.00	D
Restricted Stock Unit	(2)	(2)	Common Stock	99	$0.00	D
Restricted Stock Unit	(3)	(3)	Common Stock	809	$0.00	D
Restricted Stock Unit	(4)	(4)	Common Stock	1,003	$0.00	D
Restricted Stock Unit	(5)	(5)	Common Stock	30,027	$0.00	D
Restricted Stock Unit	(6)	(6)	Common Stock	10,061	$0.00	D
Restricted Stock Unit	(7)	(7)	Common Stock	3,251	$0.00	D
Restricted Stock Unit	(8)	(8)	Common Stock	1,797	$0.00	D
Restricted Stock Unit	(9)	(9)	Common Stock	74,905	$0.00	D
Stock Options (Right to buy)	(10)	07/28/2031	Common Stock	11,820	$54.04	D
Stock Options (Right to buy)	(11)	04/07/2032	Common Stock	10,543	$29.62	D
Stock Options (Right to buy)	(12)	02/02/2034	Common Stock	21,852	$23.1	D
Stock Options (Right to buy)	(13)	05/21/2034	Common Stock	60,123	$16.78	D
Stock Options (Right to buy)	(14)	02/06/2033	Common Stock	9,168	$14.89	D
Stock Options (Right to buy)	(15)	03/15/2033	Common Stock	15,320	$11.89	D
Stock Options (Right to buy)	(16)	09/23/2032	Common Stock	14,649	$9.67	D
Stock Options (Right to buy)	(17)	02/04/2035	Common Stock	131,147	$8.43	D

Explanation of Responses:

1. On February 15, 2026, the reporting person was granted 74,905 Performance Stock Units, with each PSU award to vest (subject to the employee's continued service to the Company on the applicable vesting dates) according to the schedule and conditions set forth in the executive long-term incentive plan contained in the Company's 2026 Employee Equity Guidelines. After the award's performance conditions are satisfied, the PSUs will vest in four equal annual installments on each of the first four anniversaries of the grant date

2. On April 7, 2022, the reporting person was granted 4,518 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 final day of each month thereafter.

3. On September 23, 2022, the reporting person was granted 6,278 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 final day of each month thereafter.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. On February 15, 2026, the reporting person was granted 74,905 restricted stock units, vesting 25% per year for four years.

10. On July 28, 2021, the reporting person was granted 11,820 stock options, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the final day of each month thereafter.

11. On April 7, 2022, the reporting person was granted 10,543 stock options, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the final day of each month thereafter.

12. On February 2, 2024, the reporting person was granted 21,852 stock options, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the final day of each month thereafter.

13. On May 21, 2024, the reporting person was granted 60,123 stock options, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the final day of each month thereafter.

14. On February 6, 2023, the reporting person was granted 9,168 stock options, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the final day of each month thereafter.

15. On March 15, 2023, the reporting person was granted 15,320 stock options, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the final day of each month thereafter.

16. On September 23, 2022, the reporting person was granted 14,649 stock options, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the final day of each month thereafter.

17. On February 4, 2025, the reporting person was granted 131,147 stock options, vesting 25% on the first anniversary of the grant date, with the remaining 75% vesting in 36 equal monthly installments on the final day of each month thereafter.

Remarks:

	/s/ Bonnie McManus, Attorney-in-Fact	03/05/2026
	** 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 5 (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 does the Form 3 filing by Quanterix (QTRX) COO Michael Francis Miller show?

The Form 3 shows Michael Francis Miller’s existing equity interests in Quanterix, including Performance Stock Units, multiple Restricted Stock Unit grants, several stock option awards, and directly owned Common Stock. It is an initial ownership report, not a record of new share purchases or sales.

How many Performance Stock Units does the Quanterix (QTRX) COO hold?

Michael Francis Miller holds 74,905 Performance Stock Units granted on February 15, 2026. These PSUs vest in four equal annual installments after specified performance conditions are satisfied, and are governed by the company’s 2026 Employee Equity Guidelines and long-term incentive plan.

What Restricted Stock Units are disclosed for the Quanterix (QTRX) COO?

The filing lists several RSU awards, including 74,905 Restricted Stock Units granted on February 15, 2026 that vest 25% per year for four years. Earlier RSU grants from 2022–2025 vest 25% after one year, with the remaining 75% vesting in 36 monthly installments.

What stock options does Quanterix (QTRX) COO Michael Francis Miller hold?

He holds several stock option grants to buy Common Stock, with exercise prices ranging from $8.4300 to $54.0400 per share. These options were granted between July 28, 2021 and February 4, 2025 and expire between 2031 and 2035, following standard multi-year vesting schedules.

Does the Quanterix (QTRX) Form 3 show any insider share purchases or sales?

No, the Form 3 records existing holdings, not new trades. All entries are categorized as holdings, and the transaction summary shows no buy, sell, exercise, gift, or tax-withholding transactions, only positions in PSUs, RSUs, stock options, and Common Stock.

How many Quanterix (QTRX) common shares does the COO directly own?

The filing states that Michael Francis Miller directly owns 30,262 shares of Quanterix Common Stock as of the reporting date. This common share position is separate from his Performance Stock Units, Restricted Stock Units, and stock option awards disclosed in the same Form 3.