X0306 4 2017-11-20 0 0001501697 Arsanis, Inc. ASNS 0001117003 MCGUIRE TERRANCE C/O POLARIS PARTNERS ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 1 0 1 0 Common Stock 2017-11-20 4 C 0 18848 A 18848 I See Footnotes Common Stock 2017-11-20 4 C 0 367 A 367 I See Footnote Common Stock 2017-11-20 4 C 0 129 A 129 I See Footnote Common Stock 2017-11-20 4 C 0 188 A 188 I See Footnote Common Stock 2017-11-20 4 C 0 243385 A 262233 I See Footnotes Common Stock 2017-11-20 4 C 0 4743 A 5110 I See Footnote Common Stock 2017-11-20 4 C 0 1667 A 1796 I See Footnote Common Stock 2017-11-20 4 C 0 2433 A 2621 I See Footnote Common Stock 2017-11-20 4 C 0 317376 A 579609 I See Footnotes Common Stock 2017-11-20 4 C 0 6185 A 11295 I See Footnote Common Stock 2017-11-20 4 C 0 2173 A 3969 I See Footnote Common Stock 2017-11-20 4 C 0 3173 A 5794 I See Footnote Common Stock 2017-11-20 4 C 0 110312 A 689921 I See Footnotes Common Stock 2017-11-20 4 C 0 2150 A 13445 I See Footnote Common Stock 2017-11-20 4 C 0 755 A 4724 I See Footnote Common Stock 2017-11-20 4 C 0 1102 A 6896 I See Footnote Common Stock 2017-11-20 4 C 0 631041 A 1320962 I See Footnotes Common Stock 2017-11-20 4 C 0 12298 A 25743 I See Footnote Common Stock 2017-11-20 4 C 0 4322 A 9046 I See Footnote Common Stock 2017-11-20 4 C 0 6310 A 13206 I See Footnote Common Stock 2017-11-20 4 P 0 482467 10.00 A 1803429 I See Footnotes Common Stock 2017-11-20 4 P 0 9403 10.00 A 35146 I See Footnote Common Stock 2017-11-20 4 P 0 3305 10.00 A 12351 I See Footnote Common Stock 2017-11-20 4 P 0 4825 10.00 A 18031 I See Footnote Series A-1 Convertible Preferred Stock 2017-11-20 4 C 0 64329 0.00 D Common Stock 18848 0 I See Footnotes Series A-1 Convertible Preferred Stock 2017-11-20 4 C 0 1254 0.00 D Common Stock 367 0 I See Footnote Series A-1 Convertible Preferred Stock 2017-11-20 4 C 0 441 0.00 D Common Stock 129 0 I See Footnote Series A-1 Convertible Preferred Stock 2017-11-20 4 C 0 643 0.00 D Common Stock 188 0 I See Footnote Series A-2 Convertible Preferred Stock 2017-11-20 4 C 0 680130 0.00 D Common Stock 243385 0 I See Footnotes Series A-2 Convertible Preferred Stock 2017-11-20 4 C 0 13256 0.00 D Common Stock 4743 0 I See Footnote Series A-2 Convertible Preferred Stock 2017-11-20 4 C 0 4659 0.00 D Common Stock 1667 0 I See Footnote Series A-2 Convertible Preferred Stock 2017-11-20 4 C 0 6801 0.00 D Common Stock 2433 0 I See Footnote Series B Convertible Preferred Stock 2017-11-20 4 C 0 710817 0.00 D Common Stock 317376 0 I See Footnotes Series B Convertible Preferred Stock 2017-11-20 4 C 0 13854 0.00 D Common Stock 6185 0 I See Footnote Series B Convertible Preferred Stock 2017-11-20 4 C 0 4869 0.00 D Common Stock 2173 0 I See Footnote Series B Convertible Preferred Stock 2017-11-20 4 C 0 7108 0.00 D Common Stock 3173 0 I See Footnote Series C Convertible Preferred Stock 2017-11-20 4 C 0 221638 0.00 D Common Stock 110312 0 I See Footnotes Series C Convertible Preferred Stock 2017-11-20 4 C 0 4315 0.00 D Common Stock 2150 0 I See Footnote Series C Convertible Preferred Stock 2017-11-20 4 C 0 1516 0.00 D Common Stock 755 0 I See Footnote Series C Convertible Preferred Stock 2017-11-20 4 C 0 2213 0.00 D Common Stock 1102 0 I See Footnote Series D Convertible Preferred Stock 2017-11-20 4 C 0 2153746 0.00 D Common Stock 631041 0 I See Footnotes Series D Convertible Preferred Stock 2017-11-20 4 C 0 41976 0.00 D Common Stock 12298 0 I See Footnote Series D Convertible Preferred Stock 2017-11-20 4 C 0 14752 0.00 D Common Stock 4322 0 I See Footnote Series D Convertible Preferred Stock 2017-11-20 4 C 0 21537 0.00 D Common Stock 6310 0 I See Footnote The Series A-1 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 A-1 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. These shares are owned directly by Polaris Venture Partners V, L.P. ("Polaris V"), whose general partner is Polaris Venture Management Co. V, L.L.C. ("Polaris Management"). Each of Jonathan A. Flint ("Flint") and the Reporting Person, are the managing members of Polaris Management and may each be deemed to share voting and dispositive power with respect to the shares held by each of Polaris V, Polaris Venture Partners Entrepreneurs' Fund V, L.P. ("Polaris Entrepreneurs' V"), Polaris Venture Partners Founders' Fund V, L.P. ("Polaris Founders' V") and Polaris Venture Partners Special Founders' Fund V, L.P. ("Polaris Special Founders' V", and together with Polaris V, Polaris Entrepreneurs' V and Polaris Founders' V, the "Polaris V Funds"). (Continued from footnote 2) Polaris Management may be deemed to have sole power to vote and dispose of the shares held by the Polaris V Funds. Each of Flint, the Reporting Person and Polaris Management disclaims beneficial ownership of these securities and this report shall not be deemed to be an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or any other purpose, except to the extent of their respective pecuniary interests therein. These shares are owned directly by Polaris Entrepreneurs' V, whose general partner is Polaris Management. Each of Flint and the Reporting Person are the managing members of Polaris Management and may each be deemed to share voting and dispositive power over the shares held by each of the Polaris V Funds. Polaris Management may be deemed to have sole power to vote and dispose of the shares held by the Polaris V Funds. Each of Flint, the Reporting Person and Polaris Management disclaims beneficial ownership of these securities and this report shall not be deemed to be an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or any other purpose, except to the extent of their respective pecuniary interests therein. These shares are owned directly by Polaris Founders' V, whose general partner is Polaris Management. Each of Flint and the Reporting Person are the managing members of Polaris Management and may each be deemed to share voting and dispositive power over the shares held by each of the Polaris V Funds. Polaris Management may be deemed to have sole power to vote and dispose of the shares held by the Polaris V Funds. Each of Flint, the Reporting Person and Polaris Management disclaims beneficial ownership of these securities and this report shall not be deemed to be an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or any other purpose, except to the extent of their respective pecuniary interests therein. These shares are owned directly by Polaris Special Founders' V, whose general partner is Polaris Management. Each of Flint and the Reporting Person are the managing members of Polaris Management and, may each be deemed to share voting and dispositive power over the shares held by each of the Polaris V Funds. Polaris Management may be deemed to have sole power to vote and dispose of the shares held by the Polaris V Funds. Each of Flint, the Reporting Person and Polaris Management disclaims beneficial ownership of these securities and this report shall not be deemed to be an admission that any of them is the beneficial owner of such securities for purposes of Section 16 or any other purpose, except to the extent of their respective pecuniary interests therein. The Series A-2 Convertible Preferred Stock converted into Common Stock on a 0.35785-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A-2 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 B Convertible Preferred Stock converted into Common Stock on a 0.44650-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series B 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 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. /s/ Mike Gray, attorney-in-fact 2017-11-20