“Is it Open Source? No. Datomic binaries are provided under the Apache 2 license which grants all the same rights to a work delivered in object form.”
Nubank put Datomic’s binaries under Apache 2.0 and kept the source to itself. You can redistribute the jar. You cannot read it, fix it or fork it. Datomic stays a critical piece of Nubank’s own infrastructure, and the money now comes from enterprise support contracts. Free as in beer, closed as in vault.