X0306 4 2019-05-16 0 0001651235 Acacia Communications, Inc. ACIA 0001657394 Reiss Stan J C/O MATRIX PARTNERS VIII, L.P. 101 MAIN STREET, 17TH FLOOR CAMBRIDGE MA 02142 1 0 0 0 Common Stock 2019-05-16 4 A 0 4010 0.00 A 194002 D Common Stock 23002 I By The Reiss Family Irrevocable Trust Consists of 4,010 restricted stock units ("RSUs") awarded to the Reporting Person as compensation for services rendered as a director. Each RSU represents the right to receive one share of common stock upon vesting. The RSUs will vest as to 100% of the original number of shares on May 16, 2020. Includes 4,010 RSUs (the 4,010 RSUs described in footnote 1). Each RSU represents the right to receive one share of common stock upon vesting. Shares held by The Reiss Family Irrevocable Trust. The Reporting Person is a trustee and beneficiary of the trust. /s/ Stan Reiss 2019-05-20