Summary The model haloarchaeon, Haloferax volcanii possess an extremely high, and highly specific, basal caspase activity in exponentially growing cells that closely resembles caspase‐4. This activity is specifically inhibited by the pan‐caspase inhibitor, z‐VAD‐FMK, and has no cross‐reactivity with other known protease families. Although it is one of the dominant cellular proteolytic activities in exponentially growing H. vol...