There's on-prem which is the original model, and then the newer Datomic Cloud (came about in ~2018) which is installed from AWS Marketplace and billed through AWS. There are some feature differences between them. With on-prem there are free and $$ licensing options. Might be that the on-prem gratis licensing options were more limited before.

Some of the cool kids in Clojure world seem to have moved over to XTDB these days.