X0306 4 2017-11-15 0 0001501697 Arsanis, Inc. ASNS 0001282930 GORDON CARL L C/O ARSANIS, INC. 890 WINTER STREET, SUITE 230 WALTHAM MA 02451 1 0 1 0 Stock Option (right to buy) 10.00 2017-11-15 4 A 0 7324 0.00 A 2027-11-14 Common Stock 7324 7324 D Consists of an automatic stock option grant that was made on November 15, 2017, the date of the effectiveness of the registration statement for the issuer's initial public offering, under the issuer's director compensation program. The option becomes exercisable as to 33.3333% of the shares underlying the award on the first anniversary of the date of grant, with the remainder vesting in equal monthly installments until the third anniversary of the date of grant, subject to the Reporting Person's continued service as a director through each applicable vesting date. /s/ Rene Russo, attorney-in-fact 2017-12-01