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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).
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