X0206 3 2017-11-15 0 0001501697 Arsanis, Inc. ASNS 0001439589 Polaris Venture Management Co. V, L.L.C. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 0 0 1 0 0001439590 Polaris Venture Partners V, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 0 0 1 0 0001439587 Polaris Venture Partners Entrepreneurs' Fund V, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 0 0 1 0 0001439588 Polaris Venture Partners Founders' Fund V, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 0 0 1 0 0001439586 Polaris Venture Partners Special Founders' Fund V, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 0 0 1 0 0001295676 Flint Jonathan A ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON MA 02210 0 0 1 0 Series A-1 Convertible Preferred Stock Common Stock 18848 I See Footnotes Series A-1 Convertible Preferred Stock Common Stock 367 I See Footnote Series A-1 Convertible Preferred Stock Common Stock 129 I See Footnote Series A-1 Convertible Preferred Stock Common Stock 188 I See Footnote Series A-2 Convertible Preferred Stock Common Stock 243385 I See Footnotes Series A-2 Convertible Preferred Stock Common Stock 4743 I See Footnote Series A-2 Convertible Preferred Stock Common Stock 1667 I See Footnote Series A-2 Convertible Preferred Stock Common Stock 2433 I See Footnote Series B Convertible Preferred Stock Common Stock 317376 I See Footnotes Series B Convertible Preferred Stock Common Stock 6185 I See Footnote Series B Convertible Preferred Stock Common Stock 2173 I See Footnote Series B Convertible Preferred Stock Common Stock 3173 I See Footnote Series C Convertible Preferred Stock Common Stock 110312 I See Footnotes Series C Convertible Preferred Stock Common Stock 2150 I See Footnote Series C Convertible Preferred Stock Common Stock 755 I See Footnote Series C Convertible Preferred Stock Common Stock 1102 I See Footnote Series D Convertible Preferred Stock Common Stock 631041 I See Footnotes Series D Convertible Preferred Stock Common Stock 12298 I See Footnote Series D Convertible Preferred Stock Common Stock 4322 I See Footnote Series D Convertible Preferred Stock Common Stock 6310 I See Footnote The Series A-1 Convertible Preferred Stock is convertible into Common Stock on a 0.29300-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have 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 Terrance G. McGuire ("McGuire"), who is a member of the Issuer's Board of Directors and whose beneficial ownership is reported on a separate Form 3, 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"). Polaris Management may be deemed to have sole power to vote and dispose of the shares held by the Polaris V Funds. (Continued from footnote 2) Each of Flint, McGuire 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 McGuire 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, McGuire 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 McGuire 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, McGuire 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 McGuire 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, McGuire 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 is convertible into Common Stock on a 0.35785-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. The Series B Convertible Preferred Stock is convertible into Common Stock on a 0.44650-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. The Series C Convertible Preferred Stock is convertible into Common Stock on a 0.49832-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. The Series D Convertible Preferred Stock is convertible into Common Stock on a 0.29300-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. /s/ Max Eisenberg, Attorney-in-Fact for Polaris Ventures Management Co. V., L.L.C. 2017-11-15 /s/ Max Eisenberg, Attorney-in-Fact for Polaris Venture Partners V, L.P. 2017-11-15 /s/ Max Eisenberg, Attorney-in-Fact for Polaris Venture Partners Entrepreneurs' Fund V, L.P. 2017-11-15 /s/ Max Eisenberg, Attorney-in-Fact for Polaris Venture Partners Founders' Fund V 2017-11-15 /s/ Max Eisenberg, Attorney-in-Fact for Polaris Venture Partners Special Founders' Fund V, L.P. 2017-11-15 /s/ Max Eisenberg, Attorney-in-Fact for Jonathan Flint 2017-11-15