X0508 4 2026-02-06 0001701108 Spero Therapeutics, Inc. SPRO 0001798155 Keutzer Timothy C/O SPERO THERAPEUTICS, INC. 675 MASSACHUSETTS AVENUE, 14TH FLOOR CAMBRIDGE MA 02139 false true false false Chief Operating Officer false Common Stock 2026-02-06 4 S false 18652 2.36 D 742506 D Represents shares required to be sold by the Reporting Person to cover tax withholding obligations in connection with the vesting of RSUs. The sale occurred automatically to satisfy the tax withholding obligations to be funded by a "sell to cover" transaction and does not represent a discretionary trade by the Reporting Person. /s/ Maegan Deare, Attorney-in-Fact for Timothy Keutzer 2026-02-09