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Summary Inflammasomes activate the protease caspase-1, which cleaves interleukin-1β and interleukin-18 to generate the mature cytokines and controls their secretion and a form of inflammatory cell death called pyroptosis. By generating mice expressing enzymatically inactive caspase-1C284A, we provide genetic evidence that caspase-1 protease activity is required for canonical IL-1 secretion, pyroptosis, and inflammasome-mediated immunity. In caspase-1-deficient cells, caspase-8 can be activated at the inflammasome. Using mice either lacking the pyroptosis effector gasdermin D (GSDMD) or expressing caspase-1C284A, we found that GSDMD-dependent pyroptosis prevented caspase-8 activation at the inflammasome. In the absence of GSDMD-dependent pyroptosis, the inflammasome engaged a delayed, alternative form of lytic cell death that was accompanied by the release of large amounts of mature IL-1 and contributed to host protection. Features of this cell death modality distinguished it from apoptosis, suggesting it may represent a distinct form of pro-inflammatory regulated necrosis., Graphical Abstract, Highlights • Interplay of caspase-1 and caspase-8 revealed by analysis of Caspase1C284A mice • GSDMD-dependent pyroptosis suppresses caspase-8 activation at the inflammasome • The inflammasome engages caspase-8-driven secondary pyroptosis and IL-1 release • GSDMD-independent mechanisms contribute to inflammasome-mediated host protection, Schneider et al. show that, in the absence of GSDMD or caspase-1 protease activity (e.g., in Casp1C284A mice), the inflammasome engages an alternative type of lytic cell death and IL-1 release that contributes to immunity against infection. This secondary form of pyroptosis is dependent on apoptotic caspase activity but distinct from apoptosis.