akkadotnet/akka.net 1.6.0-beta6

Akka.NET v1.6.0-beta6

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1.6.0-beta6 November 7th, 2026

Akka.NET 1.6.0-beta6 adds top-level C# 15 union serialization and makes distributed data the default store for cluster sharding coordinator state. Read the v1.6 getting started guide for the full upgrade path.

Serialization V2

• C# 15 unions can now be sent or persisted as top-level messages with [AkkaSerializable(Manifest = "...")]. Deserialization reconstructs the boxed union, so Receive<TUnion> and Recover<TUnion> handlers continue to match. Closed generic unions register each construction with [AkkaSerializerIncludes<T>]. Standalone cases retain their own manifests, and explicitly included types discovered in referenced assemblies no longer cause duplicate registrations. (#8908, fixes #8906)
• Top-level unions use their own manifest with the existing union-field payload frame. Writing default(TUnion) at the top level throws SerializationException; field nil semantics are unchanged. AKKASG051 now requires an explicit manifest on a marked union. Reordering cases preserves the wire format; adding cases requires readers to upgrade before writers use them, and removing cases prevents reading stored values of those cases. Switching between a union and a closed hierarchy still requires a migration for top-level messages. (#8908)

Akka.Cluster.Sharding - behavior change

• akka.cluster.sharding.state-store-mode now defaults to ddata instead of persistence. Coordinator state is replicated through Akka.DistributedData. The previous default silently used the in-memory journal when no durable journal was configured, losing coordinator state when the coordinator moved. (#8905, addresses #8903)
• Migration: set akka.cluster.sharding.state-store-mode = persistence explicitly to preserve the previous behavior. With remember-entities = on, the new default follows remember-entities-store, which defaults to ddata, rather than forcing the event-sourced store. Set akka.cluster.sharding.remember-entities-store = eventsourced to keep reading remembered entities from the journal. See the v1.6 breaking-change ledger. (#8905)

2 contributors since release 1.6.0-beta5