Sec Form 4 Filing - ARCH VENTURE FUND VI LP @ Quanterix Corp - 2020-11-20

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person ARCH VENTURE FUND VI LP 2. Issuer Name and Ticker or Trading Symbol Quanterix Corp [ QTRX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 8755 WEST HIGGINS ROAD, SUITE 1025, 3. Date of Earliest Transaction (MM/DD/YY) 11/20/2020 (Street) CHICAGO, IL60631 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 11/20/2020 J( 1 ) 229,006 D $ 0 2,182,995 I See Footnote ( 2 ) Common Stock 11/20/2020 J( 1 ) 145,994 D $ 0 1,391,690 I See Footnote ( 3 ) Common Stock 11/20/2020 J( 1 )( 4 ) 854 A $ 0 854 D ( 5 ) Common Stock 11/20/2020 J( 1 )( 4 ) 853 A $ 0 853 D ( 6 ) Common Stock 11/24/2020 J( 1 ) 277,514 D $ 0 1,905,481 I See Footnote ( 2 ) Common Stock 11/24/2020 J( 1 ) 176,920 D $ 0 1,214,770 I See Footnote ( 3 ) Common Stock 11/24/2020 J( 1 )( 4 ) 1,034 A $ 0 1,888 D ( 5 ) Common Stock 11/24/2020 J( 1 )( 4 ) 1,036 A $ 0 1,889 D ( 6 )

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 7. Title and Amount of Underlying Securities (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 of Derivative Security: 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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other ARCH VENTURE FUND VI LP 8755 WEST HIGGINS ROAD, SUITE 1025 CHICAGO, IL60631 X ARCH Venture Fund VIII Overage, L.P. 8755 WEST HIGGINS ROAD, SUITE 1025 CHICAGO, IL60631 X ARCH VENTURE PARTNERS VI LP 8755 WEST HIGGINS ROAD, SUITE 1025 CHICAGO, IL606031 X ARCH VENTURE PARTNERS VI LLC 8755 WEST HIGGINS ROAD, SUITE 1025 CHICAGO, IL606031 X ARCH Venture Partners VIII, LLC 8755 WEST HIGGINS ROAD, SUITE 1025 CHICAGO, IL606031 X BYBEE CLINTON C/O ARCH VENTURE PARTNERS IX, LLC 8755 W. HIGGINS ROAD, SUITE 1025 CHICAGO, IL60631 X NELSEN ROBERT 8755 W. HIGGINS ROAD, SUITE 1025 CHICAGO, IL60631 X Signatures /s/ Mark McDonnell, as Attorney-in-Fact for ARCH Venture Fund VI, L.P. 11/24/2020 Signature of Reporting Person Date /s/ Mark McDonnell, as Attorney-in-Fact for ARCH Venture Fund VIII Overage, L.P. 11/24/2020 Signature of Reporting Person Date /s/ Mark McDonnell, as Attorney-in-Fact for ARCH Venture Partners VI, L.P. 11/24/2020 Signature of Reporting Person Date /s/ Mark McDonnell, as Attorney-in-Fact for ARCH Venture Partners VI, LLC 11/24/2020 Signature of Reporting Person Date /s/ Mark McDonnell, as Attorney-in-Fact for ARCH Venture Partners VIII, LLC 11/24/2020 Signature of Reporting Person Date /s/ Mark McDonnell, as Attorney-in-Fact for Clinton Bybee 11/24/2020 Signature of Reporting Person Date /s/ Mark McDonnell, as Attorney-in-Fact for Robert Nelsen 11/24/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Distribution of Common Stock held by a limited partnership to its partners for no consideration. ( 2 )These shares are directly held by ARCH Venture Fund VI, L.P. ("ARCH VI"). ARCH Venture Partners VI, L.P. ("GPLP"), the sole general partner of ARCH VI, may be deemed to beneficially own the shares held by ARCH VI. ARCH Venture Partners VI, LLC ("GPLLC"), as the sole general partner of GPLP, may be deemed to beneficially own the shares held by ARCH VI. As managing directors of GPLLC, each of Robert Nelsen and Clinton Bybee (the "ARCH Managing Directors"), may be deemed to beneficially own the shares held by ARCH VI. Each of GPLP, GPLLC and the ARCH Managing Directors disclaims beneficial ownership of the securities reported herein, except to the extent of their pecuniary interest therein, if any. ( 3 )The shares are held of record by ARCH Venture Fund VIII Overage, L.P. ("ARCH Fund Overage"). The sole general partner of ARCH Fund Overage is ARCH Venture Partners VIII, LLC ("ARCH VIII LLC"), which may be deemed to beneficially own the shares held by ARCH Fund Overage. ARCH VIII LLC disclaims beneficial ownership of such shares, except to the extent of any pecuniary interest therein. As managing directors of ARCH VIII LLC, each of the ARCH Managing Directors may be deemed to beneficially own the shares held by ARCH Overage. Each of ARCH VIII LLC and the ARCH Managing Directors disclaims beneficial ownership of the securities reported herein, except to the extent of their pecuniary interest therein, if any. ( 4 )Change from indirect to direct ownersh ip of shares previously reported as beneficially owned by the Reporting Person. ( 5 )Shares owned by Nelsen. ( 6 )Shares owned by Bybee.

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).

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