X0306 4 2016-10-13 0 0001651235 Acacia Communications, Inc. ACIA 0001239366 CHUNG PETER Y C/O SUMMIT PARTNERS 222 BERKELEY STREET, 18TH FLOOR BOSTON MA 02116 1 0 0 0 Common Stock 2016-10-13 4 S 0 346202 96.5 D 2550127 I See Footnotes Represents shares sold by the following entities: 262,832 shares sold by Summit Partners Venture Capital Fund III-A, L.P., 79,661 shares sold by Summit Partners Venture Capital Fund III-B, L.P., 3,424 shares sold by Summit Investors I, LLC and 285 shares sold by Summit Investors I (UK), L.P. Represents the offering price to the public of $100 per share, net of underwriters' discount of $3.50. Consists of 1,936,021 shares held by Summit Partners Venture Capital Fund III-A, L.P., 586,781 shares held by Summit Partners Venture Capital Fund III-B, L.P., 25,224 shares held by Summit Investors I, LLC and 2,101 shares held by Summit Investors I (UK), L.P. 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. 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. Mr. Chung is a member of Summit Master Company, LLC. Mr. Chung may be deemed to share beneficial ownership of the shares of the Issuer held of record by the Summit entities and has an indirect pecuniary interest in such shares through his membership in Summit Master Company, LLC. Mr. Chung expressly disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein. /s/ Robin W. Devereux, Power of Attorney for Peter Y. Chung 2016-10-14