No. Unlike with sharding, Datomic data can be read and queried from any node. However, you can route requests so that groups develop hot caches for different workloads. This provides horizontal scaling without the compromises typically associated with sharding. In particular:
You make no up-front decisions about where data will live.
Your programming model is not polluted by any awareness of where data lives.
At any time (and long after transacting your data), you can start new groups and route queries to them.