X0306 4 2017-11-20 1 0001501697 Arsanis, Inc. ASNS 0001722201 GV 2016 GP, L.L.C. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW CA 94043 0 0 1 0 0001722204 GV 2016 GP, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW CA 94043 0 0 1 0 0001721789 GV 2016, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW CA 94043 0 0 1 0 0001652044 Alphabet Inc. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW CA 94043 0 0 1 0 Common Stock 2017-11-20 4 C 0 451362 A 451362 I By GV 2016, L.P. Series D Convertible Preferred Stock 2017-11-20 4 C 0 1540499 D Common Stock 451362 0 I By GV 2016, L.P. The shares of Series D Convertible Preferred Stock beneficially owned by the Reporting Persons converted into Common Stock on a 0.29300-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series D Convertible Preferred Stock was convertible at any time at the holder's election and automatically upon the closing at the Issuer's initial public offering. The shares had no expiration date. The reported securities are directly held by GV 2016, L.P. GV 2016 GP, L.P., the general partner of GV 2016, L.P., GV 2016 GP, L.L.C., the general partner of GV 2016 GP, L.P., Alphabet Holdings LLC, the sole member of GV 2016 GP, L.L.C., XXVI Holdings Inc., the managing member of Alphabet Holdings LLC, and Alphabet Inc., the sole stockholder of XXVI Holdings Inc., may each be deemed to have sole power to vote or dispose of these shares. Each of GV 2016 GP, L.P., GV 2016 GP, L.L.C., Alphabet Holdings LLC, XXVI Holdings Inc. and Alphabet Inc. disclaim beneficial ownership of the shares except to the extent of any pecuniary interest therein. /s/ Mike Gray, as attorney-in-fact on behalf of GV 2016, L.P. 2015-11-20 /s/ Mike Gray, as attorney-in-fact on behalf of GV 2016 GP, L.P. 2015-11-20 /s/ Mike Gray, as attorney-in-fact on behalf of GV 2016 GP, L.L.C 2015-11-20 /s/ Mike Gray, as attorney-in-fact on behalf of Alphabet Inc. 2015-11-20