Sec Form 4 Filing - SUMMIT PARTNERS L P @ Acacia Communications, Inc. - 2016-05-18

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 SUMMIT PARTNERS L P 2. Issuer Name and Ticker or Trading Symbol Acacia Communications, Inc. [ ACIA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) X __ Other (specify below) Manager of GP of 10% owner (Last) (First) (Middle) 222 BERKELEY STREET, 18TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 05/18/2016 (Street) BOSTON, MA02116 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 05/18/2016 C 2,896,329 A 2,896,329 ( 2 ) I See Footnotes. ( 3 ) ( 4 )

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 Series D Convertible Preferred Stock ( 1 ) 05/18/2016 C 2,896,329 ( 1 ) ( 1 ) Common Stock 2,896,329 ( 2 ) $ 0 ( 1 ) 0 I See Footnotes ( 3 ) ( 4 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other SUMMIT PARTNERS L P 222 BERKELEY STREET 18TH FLOOR BOSTON, MA02116 X Manager of GP of 10% owner SUMMIT PARTNERS VC III, LP 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 GP of 10% owner SUMMIT PARTNERS VC III, LLC 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 Manager of GP of 10% owner SUMMIT MASTER COMPANY, LLC 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 Manager of Manager of 10% owne Summit Investors Management, LLC 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 Manager and GP of 10% Owner Summit Partners Venture Capital Fund III-A, L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Summit Partners Venture Capital Fund III-B, L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Summit Investors I, LLC 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Summit Investors I (UK), L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Signatures Summit Partners, L.P., by Summit Master Company, LLC, its GP, by /s/ Robin W. Devereux, Member 05/20/2016 Signature of Reporting Person Date Summit Partners VC III, L.P., by Summit Partners VC III, LLC, its GP, by Summit Partners, L.P., its Managing Member, by Summit Master Company, LLC, its GP, by /s/ Robin W. Devereux, Member 05/20/2016 Signature of Reporting Person Date Summit Partners VC III, LLC, by Summit Partners, L.P., its Managing Member, by Summit Master Company, LLC, its GP, by /s/ Robin W. Devereux, Member 05/20/2016 Signature of Reporting Person Date Summit Master Company, LLC, by /s/ Robin W. Devereux, Member 05/20/2016 Signature of Reporting Person Date Summit Investors Management, LLC, by Summit Master Company, LLC, its Managing Member, by /s/ Robin W. Devereux, Member 05/20/2016 Signature of Reporting Person Date Summit Partners Venture Capital Fund III-A, L.P., by Summit Partners VC III, L.P., its GP, by Summit Partners VC III, LLC, its GP, by Summit Partners, L.P., its Managing Member, by Summit Master Company, LLC, its GP, by /s/ Robin W. Devereux, Member 05/20/2016 Signature of Reporting Person Date Summit Partners Venture Capital Fund III-B, L.P., by Summit Partners VC III, L.P., its GP, by Summit Partners VC III, LLC, its GP, by Summit Partners, L.P., its Managing Member, by Summit Master Company, LLC, its GP, by /s/ Robin W. Devereux, Member 05/20/2016 Signature of Reporting Person Date Summit Investors I, LLC, by Summit Investors Management, LLC, its Manager, by Summit Master Company, LLC, its Managing Member, by /s/ Robin W. Devereux, Member 05/20/2016 Signature of Reporting Person Date Summit Investors I (UK), L.P., by Summit Investors Management, LLC, its General Partner, by Summit Master Company, LLC, its Managing Member, by /s/ Robin W. Devereux, Member 05/20/2016 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The Series D Convertible Preferred Stock converted into common stock on a one-for-one basis upon the closing of Acacia Communications, Inc.'s (the "Issuer") initial public offering without payment of consideration. The Series D Convertible Preferred Stock had no expiration date. ( 2 )Consists of 2,198,853 shares held by Summit Partners Venture Capital Fund III-A. L.P., 666,442 shares held by Summit Partners Venture Capital Fund III-B, L.P., 28,648 shares held by Summit Investors I, LLC and 2,386 shares held by Summit Investors I (UK), L.P. ( 3 )Summit Partners, L.P. is the managing member of Summit Partners VC III, LLC, which is the general partner of Summit Partners VC III, L.P., which is the general partner of each of Summit Partners Venture Capital Fund III-A. L.P. and Summit Partners Venture Capital Fund III-B, L.P. Summit Master Company, LLC is the managing member of Summit Investors Management, LLC, which is the manager of Summit Investors I, LLC, and the general partner of Summit Investors I (UK), L.P. Summit Master Company, LLC, as the managing member of Summit Investors Management, LLC, has delegated investment decisions, including voting and dispositive power, to Summit Partners, L.P. and its investment committee responsible for voting and investment decisions with respect to the Issuer. ( 4 )Summit Partners, L.P., through a three-person investment committee responsible for voting and investment decisions with respect to the Issuer, currently comprised of Martin J. Mannion, Bruce R. Evans and Peter Y. Chung, has voting and dispositive power over the shares held by each of these entities and therefore may be deemed to beneficially own such shares. Each of the Summit entities mentioned herein and Messrs. Mannion, Evans and Chung disclaims beneficial ownership of the shares, except, in each case, to the extent of each such person's pecuniary interest therein.

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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