Ac-FLTD-CMK, inhibits GSDMD cleavage by caspases-1, -4, -5, and -11 in vitro, suppresses pyroptosis downstream of both canonical and noncanonical inflammasomes, as well as reduces IL-1β release following activation of the NLRP3 inflammasome in macrophages. By contrast, Ac-FLTD-CMK does not target caspase-3 or apoptotic cell death. Crystal structure of caspase-1 in complex with Ac-FLTD-CMK reveals extensive enzyme-inhibitor interactions involving both hydrogen bonds and hydrophobic contacts.