Sec Form 4 Filing - Reiss Stan J @ Acacia Communications, Inc. - 2019-03-08

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 Reiss Stan J 2. Issuer Name and Ticker or Trading Symbol Acacia Communications, Inc. [ ACIA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O MATRIX PARTNERS VIII, L.P., 101 MAIN STREET, 17TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 03/08/2019 (Street) CAMBRIDGE, MA02142 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ 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 03/08/2019 J( 1 ) 1,146,247 D $ 0 1,000,000 I By Matrix Partners VIII, L.P. ( 2 ) ( 3 ) Common Stock 03/08/2019 J( 4 ) 632 D $ 0 552 I By Weston & Co. VIII LLC ( 5 ) Common Stock 03/08/2019 J( 4 ) 632 A $ 0 42,173 I By Matrix VIII US Management Co., L.L.C. ( 3 ) Common Stock 03/08/2019 J( 6 ) 335,788 A $ 0 377,961 I By Matrix VIII US Management Co., L.L.C. ( 3 ) Common Stock 03/08/2019 J( 7 ) 331,046 D $ 0 46,915 I By Matrix VIII US Management Co., L.L.C. ( 3 ) Common Stock 03/08/2019 J( 7 ) 2,804 A $ 0 24,046 I By The Reiss Family Irrevocable Trust ( 8 ) Common Stock 03/08/2019 J( 9 ) 21,868 A $ 0 198,131 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 (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 Reiss Stan J C/O MATRIX PARTNERS VIII, L.P. 101 MAIN STREET, 17TH FLOOR CAMBRIDGE, MA02142 X Signatures /s/ Stan Reiss 03/11/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents a pro-rata distribution, and not a purchase or sale, without additional consideration by Matrix Partners VIII, L.P. ("Matrix Partners VIII"), to its partners. ( 2 )The shares are owned directly by Matrix Partners VIII. ( 3 )Matrix VIII US Management Co., L.L.C. ("Matrix VIII US Management Co.") is the General Partner of Matrix Partners VIII and disclaims beneficial ownership of the shares owned by Matrix Partners VIII except to the extent of its proportionate pecuniary interest therein. Mr. Reiss, a member of the Board of Directors of the Issuer and a managing member of Matrix VIII US Management Co., has sole voting and dispositive power with respect to these shares. Mr. Reiss disclaims beneficial ownership of such shares, except to the extent of his pecuniary interest therein. ( 4 )Re-registration of shares by Weston & Co. VIII L.L.C. ("Weston VIII"), without consideration, in the name of Matrix VIII US Management Co., the beneficial owner of those shares. ( 5 )Matrix VIII US Management Co. is the beneficial owner of the shares reported herein as being held of record by Weston VIII, and disclaims beneficial ownership of the shares owned by Weston VIII except to the extent of its proportionate pecuniary interest therein. Mr. Reiss, a member of the Board of Directors of the Issuer and a managing member of Matrix VIII US Management Co., has sole voting and dispositive power with respect to these shares. Mr. Reiss disclaims beneficial ownership of such shares, except to the extent of his pecuniary interest therein. ( 6 )Represents the shares received in connection with the pro-rata distribution by Matrix Partners VIII, without consideration to its partners. ( 7 )Represents pro-rata distribution by Matrix VIII US Management Co., without consideration, to its members. ( 8 )Shares held by The Reiss Family Irrevocable Trust. Mr. Reiss is a trustee and beneficiary of the trust. ( 9 )Represents the shares received in connection with the pro-rata distribution by Matrix VIII US Management Co., without consideration, as described in this Form 4.

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).

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