X0609 4 2026-06-23 0001701108 Spero Therapeutics, Inc. SPRO 0001378588 Deshpande Milind false C/O SPERO THERAPEUTICS, INC. 675 MASSACHUSETTS AVENUE, 14TH FLOOR CAMBRIDGE MA 02139 true false false false false Common Stock 2026-06-23 4 A false 10000 0.00 A 101454 D Stock Option (right to buy) 2.15 2026-06-23 4 A false 20000 0.00 A 2036-06-23 Common Stock 20000 20000 D Consists of restricted stock units ("RSUs"). Each RSU represents the right to receive one share of common stock upon vesting. The RSUs vest on June 23, 2027, subject to the Reporting Person's continued service through the applicable vesting date. The shares underlying this option will vest and become exercisable in full on June 23, 2027 subject to the Reporting Person's continued service as a director through the vesting date. /s/ Maegan Deare, Attorney-in-Fact for Milind Deshpande 2026-06-25