X0306 4 2017-11-20 1 0001501697 Arsanis, Inc. ASNS 0001722607 EMBL Technology Fund II GmbH & Co. KG BOXBERGRING 107 HEIDELBERG 2M 69126 GERMANY 0 0 1 0 0001722603 EMBL Ventures Verwaltungs GmbH BOXBERGRING 107 HEIDELBERG 2M 69126 GERMANY 0 0 1 0 0001722536 Adams Jan BOXBERGRING 107 HEIDELBERG 2M 69126 GERMANY 0 0 1 0 0001722440 Herr Stefan BOXBERGRING 107 HEIDELBERG 2M 69126 GERMANY 0 0 1 0 0001646114 Muhlenbeck Frank BOXBERGRING 107 HEIDELBERG 69126 0 0 1 0 Common Stock 2017-11-20 4 C 0 103278 A 103278 D Common Stock 2017-11-20 4 C 0 247176 A 350454 D Common Stock 2017-11-20 4 P 0 20000 10.00 A 370454 D Series C Convertible Preferred Stock 2017-11-20 4 C 0 207253 0.00 D Common Stock 103278 0 D Series D Convertible Preferred Stock 2017-11-20 4 C 0 843613 0.00 D Common Stock 247176 0 D The Series C Convertible Preferred Stock converted into Common Stock on a 0.49832-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series C 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 Series D Convertible Preferred Stock 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 held of record by EMBL Technology Fund II GmbH & Co. KG ("EMBL"). EMBL Ventures Verwaltungs GmbH is the general partner of EMBL. Dr. Jan Adams, Dr. Frank Muhlenbeck and Dr. Stefan Herr are the Managing Directors of EMBL Ventures Verwaltungs GmbH. By virtue of such relationships, EMBL Ventures Verwaltungs GmbH, Dr. Adams, Dr. Frank Muhlenbeck and Dr. Herr may be deemed to have voting and investment power with respect to the securities held by EMBL. Each of EMBL Ventures Verwaltungs GmbH, Dr. Adams, Dr. Frank Muhlenbeck and Dr. Herr disclaims beneficial ownership of these securities and this report shall not be deemed to be an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or any other purpose, except to the extent of their pecuniary interest therein. /s/ Mike Gray, as attorney-in-fact on behalf of EMBL Technology Fund II GmbH & Co. KG 2017-11-20 /s/ Mike Gray, as attorney-in-fact on behalf of EMBL Ventures Verwaltungs GmbH 2017-11-20 /s/ Mike Gray, as attorney-in-fact on behalf of Stefan Herr 2017-11-20 /s/ Mike Gray, as attorney-in-fact on behalf of Jan Adams 2017-11-20 /s/ Mike Gray, as attorney-in-fact on behalf of Frank Muhlenbeck 2017-11-20