X0306 4 2019-11-26 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 2019-11-26 5 G 0 E 2130 0.00 D 191872 D Common Stock 23002 I By The Reiss Family Irrevocable Trust Common Stock 50623 I By Matrix VIII US Management Co., L.L.C. Represents gifts of shares to educational institutions. Shares held by The Reiss Family Irrevocable Trust. The Reporting Person is a trustee and beneficiary of the trust. Matrix VIII US Management Co., L.L.C. ("Matrix VIII US Management Co.") is the beneficial owner of the shares. 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. /s/ Stan Reiss 2019-11-27