X0306 4 2017-03-09 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 2017-03-09 4 S 0 1250000 50.25 D 1300127 I See Footnotes Represents shares sold by the following entities: 948,982 shares sold by Summit Partners Venture Capital Fund III-A, L.P., 287,624 shares sold by Summit Partners Venture Capital Fund III-B, L.P., 12,364 shares sold by Summit Investors I, LLC and 1,030 shares sold by Summit Investors I (UK), L.P. Consists of 987,039 shares held by Summit Partners Venture Capital Fund III-A, L.P., 299,157 shares held by Summit Partners Venture Capital Fund III-B, L.P., 12,860 shares held by Summit Investors I, LLC and 1,071 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 two-person investment committee responsible for voting and investment decisions with respect to the Issuer, currently comprised of Martin J. Mannion 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. Each of Summit Partners, L.P., Mr. Mannion and Mr. Chung expressly disclaims beneficial ownership of such shares except to the extent of their pecuniary interest therein. /s/ Robin W. Devereux, Power of Attorney for Peter Y. Chung 2017-03-13