akkadotnet/akka.net 1.5.66

Akka.NET v1.5.66

on GitHub

1.5.66 April 24th, 2026

Akka.NET v1.5.66 is a significant release with persistence bug fixes, major Akka.Streams improvements including OpenTelemetry trace propagation and non-blocking materialized values, and new serialization security controls.

Akka.Streams: OpenTelemetry Trace Context Propagation

Akka.Streams now propagates System.Diagnostics.Activity trace context end-to-end through stream graphs, including across async stage boundaries, fan-in merges, and fan-out broadcasts. This enables full distributed tracing visibility into stream pipelines when using OpenTelemetry.

For full documentation, see: https://getakka.net/articles/streams/stream-tracing.html

• Akka.Streams: end-to-end OpenTelemetry trace context propagation

Akka.Streams: Non-Blocking Materialized-Value TaskCompletionSource

All TaskCompletionSource instances used for materialized values across Akka.Streams now use TaskCreationOptions.RunContinuationsAsynchronously, eliminating potential deadlocks and thread-pool starvation when continuations run synchronously on completion.

• Non-blocking materialized-value TaskCompletionSource

Akka.Persistence

• Redesign MemoryJournal and MemorySnapshotStore with channel-based drain-on-read pattern
• Ensure WriteMessagesAsync/SaveAsync is called asynchronously

Akka.Core

• Filter link-local (APIPA) addresses from DNS resolution results
• Fix multi-node adapter output race

New Features

• Add allow-unregistered-types serialization setting — when set to false, FindSerializerForType throws SerializationException if no explicit serializer binding exists, rather than falling back to the default serializer.
• Widen ActorTaskScheduler(ActorCell) ctor to protected internal

Documentation

• Surface serialization security guidance on remoting security page
• Replace TBD XML doc placeholders in Scheduler and Stash

4 contributors since release 1.5.65

To see the full set of changes in Akka.NET v1.5.66, click here.

Changes:

• ed4bd3b fix(api-approval): update Net.verified.txt files to match v1.5.66 API surface [ #8158, #8184, #8160 ]
• db7d0c6 Update RELEASE_NOTES.md for 1.5.66 release
• 30d3245 fix(persistence): redesign MemoryJournal and MemorySnapshotStore with channel-based drain-on-read pattern (#8184)
• a661450 fix: use AwaitAssert for eventually-consistent cluster state in QuickRestartSpec (#8183)
• 12c9ea0 Fix multi-node adapter output race (#8180)
• c43c9e5 Add inline comments explaining APIPA fallback behavior at both ResolveNameAsync sites
• eca0e31 Address PR review: use IEnumerable, condense tests to Theory, add debug logging
• c7388f3 fix: filter link-local (APIPA) addresses from DNS resolution results (#8178)
• f08b940 Ensure WriteMessagesAsync/SaveAsync is called asynchronously in Async… (#8163)
• 18905e4 Docs: surface serialization security guidance on the remoting security page (#8177) [ #8173 ]