# XState 6.0.0-alpha.41

- Product: XState (https://whatsnew.fyi/product/xstate)
- Vendor: Stately
- Date: 2026-08-20
- Version: 6.0.0-alpha.41
- Original notes: https://github.com/statelyai/xstate/releases/tag/xstate%406.0.0-alpha.41
- Permalink: https://whatsnew.fyi/product/xstate/releases/6.0.0-alpha.41
- Labels: Pre-release

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **added** — Actors now have deterministic, location-transparent identity with a logical address representing the path from the root
- **added** — Root actors are named after their logic's id, and children spawned without an explicit id get deterministic per-parent counters keyed by their actor source
- **added** — getEffectDescriptor(effect) returns a serializable view of any executable effect with actor references replaced by addresses
- **added** — A host runtime can be installed as system.runtime with the built-in local runtime as the default
- **added** — New deliverEvent, stopActor and terminateActor helpers expose local behaviors for custom runtimes to delegate to
- **added** — createDurable adapters carry their runtime operations directly and expose rootAddress and getActorRef(snapshot)
- **added** — getPersistedSnapshot(snapshot, { embedChildren: false }) persists children by logical address, leaving each child's state with the runtime that owns it
- **added** — Undeliverable events are reported through the new deadLetter runtime operation and a @xstate.deadletter inspection event
- **added** — A persisted remote child entry round-trips an optional opaque incarnation token to drop completions from different incarnations of the address
- **added** — createDurable exposes machineId and machineVersion so hosts can pin an execution's journal to the machine version that produced it
- **added** — Async-actor steps route through the new runStep runtime operation with a runStep helper export exposing the built-in behavior
- **added** — Serialized actor references now carry xstate$type: 'actorRef' instead of the v5 xstate$$type: 1 marker
- **added** — Timers persisted from a running actor carry their wall-clock start (startedAt) and restore by scheduling the remaining time toward the original deadline
- **changed** — Addresses are stable across persistence and restore with sessionId identifying one incarnation of an address
- **changed** — enq.spawn(actors.x) records the registered source key so spawned children persist by key
- **changed** — Explicit child ids are now unique per parent and spawning or invoking with an id already held by a live sibling throws an error
- **changed** — A transition to a history state that restores its own source now exits and reenters the source so its invoked actors restart instead of leaking
- **changed** — During executeEffects in createDurable, root-addressed events no longer reach any runtime sendEvent and should be drained from the executeEffects result instead
- **changed** — Runtime objects are wrapped before effects see them so identity comparisons and extra non-runtime properties are not preserved

###### Minor Changes

- 14cfdc3: Actors now have deterministic, location-transparent identity.
  
  - Every actor has a logical `address`: the `/`-joined path of actor ids from the root. Root actors are named after their logic's `id`, and children spawned without an explicit id get deterministic per-parent counters keyed by their actor source (`worker:0`, `worker:1`). Addresses are stable across persistence and restore; `sessionId` identifies one incarnation of an address, and completions from a previous incarnation of a local child are dropped.
  - `enq.spawn(actors.x)` records the registered source key so spawned children persist by key.
  - `getEffectDescriptor(effect)` returns a serializable view of any executable effect, with actor references replaced by addresses and actor sources by source keys (payload fields pass through by reference).
  - A host runtime can be installed as `system.runtime`; the built-in local runtime is the default. The new `deliverEvent`, `stopActor` and `terminateActor` helpers expose the local behaviors for custom runtimes to delegate to.
  - `createDurable` (from `xstate/durable`) adapters carry their runtime operations directly (`sendEvent`, `scheduleTimer`, …), and the execution installs them on every snapshot's actor system; it exposes `rootAddress` and `getActorRef(snapshot)`, tags every effect with a serializable `descriptor`, and `executeEffects` resolves only when every transitively initiated runtime operation has been accepted — returning the events addressed to the root actor for the durable loop. Breaking for existing adapters: during `executeEffects`, root-addressed events no longer reach any runtime `sendEvent` (including per-effect `runtime()` implementations) — drain them from the `executeEffects` result instead. While the loop is parked in `waitForEvent`, a root-addressed event reaches `sendEvent` like any other target, and the host should enqueue it in its own mailbox. Runtime objects are also wrapped before effects see them, so identity comparisons and extra non-runtime properties on the returned object are not preserved.
  - `getPersistedSnapshot(snapshot, { embedChildren: false })` persists children by logical address, leaving each child's state with the runtime that owns it; restoring an address-only child produces a location-transparent handle whose sends route through the system runtime.
  - Explicit child ids are unique per parent: spawning or invoking with an id already held by a live sibling throws (ids stopped earlier in the same transition stay reusable). Previously a duplicate id silently created a second running actor at the same address. A transition to a history state that restores its own source now exits and reenters the source, so its invoked actors restart instead of leaking.
  - Undeliverable events are reported through the new `deadLetter` runtime operation and a `@xstate.deadletter` inspection event. Delivery stays at-most-once — this is observability, not retry.
  - A persisted remote child entry round-trips an optional opaque `incarnation` token. XState never stamps one, but when a host does, completions from a different incarnation of the address are dropped and `sendTo` effect descriptors journal the target's token.
  - `createDurable` exposes `machineId` and `machineVersion` so hosts can pin an execution's journal to the machine version that produced it.
  - Async-actor steps (`enq.step`) route through the new `runStep` runtime operation. The built-in behavior memoizes results in the actor's own snapshot as before; a durable host implements `runStep` to own the step journal, replaying memoized results without re-running the step. The `runStep` helper export exposes the built-in behavior.
  - Serialized actor references (`Actor.toJSON`, persisted context refs) carry `xstate$type: 'actorRef'` instead of the v5 `xstate$$type: 1` marker. Migrate v5-persisted context refs with `machineVersions` if you restore them.
  - Timers persisted from a running actor ca

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