Datomic On-Prem comes in three editions - Datomic Starter, Datomic Pro, and Datomic Enterprise. Datomic Starter Edition enables small production deployments at no cost. Datomic Pro provides ongoing maintenance (software updates) as well as online support. Datomic Enterprise provides 24x7 production support, custom license terms, and integration support. You can read more about the editions here.