# NATS v2.15.0-preview.1 — Release v2.15.0-preview.1

- Product: NATS (https://whatsnew.fyi/product/nats)
- Vendor: Synadia
- Date: 2026-08-24
- Version: v2.15.0-preview.1
- Original notes: https://github.com/nats-io/nats-server/releases/tag/v2.15.0-preview.1
- Permalink: https://whatsnew.fyi/product/nats/releases/v2.15.0-preview.1
- 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** — Add desired state metalayer for JetStream streams and consumers to improve safety and reliability of asset moves and scales
- **added** — Add cancel stream move endpoint to cancel in-flight scale/move operations on a stream
- **added** — Add evacuate endpoints to safely evacuate streams and consumers from a node
- **added** — Add metalayer rescue endpoint for disaster recovery to temporarily lower quorum requirements
- **added** — Add stream backup and restore v2 format that reads per-message and correctly includes non-replicated consumers on follower nodes
- **added** — Add detection of source stream recreation to restart sourcing from the beginning
- **added** — Add stream source indexing to persist last sourced indices for instant lookup instead of expensive backward scans
- **added** — Add domain-prefixed JS API support in system account for operating on leaf nodes from hub
- **changed** — Change replicated streams with sync_interval set to always to sync WAL entries but no longer sync upper stream layer writes
- **changed** — Improve durable source and mirror consumer resets with shorter wait through heartbeat short-circuiting of recreation backoff

##### Changelog

> [!IMPORTANT]
> This is a preview release for the upcoming 2.15 series. This is not a formal release candidate and is still undergoing testing, but we would welcome feedback.

This release also contains all changes up to and including [v2.14.5](https://github.com/nats-io/nats-server/releases/tag/v2.14.5).

###### Go Version

- 1.27.0

###### Added

JetStream

- Desired state metalayer (#8432, #8437, #8439, #8443, #8452, #8460, #8476)
  - A new desired state reconciliation engine for streams and consumers considerably improves the safety and reliability of asset moves and scales
  - Updating the placement or replication factor midway through an existing scale/move operation, cancelling an in-flight scale/move, or peer-removing is now much safer
- Cancel stream move endpoint (#8476)
  - An in-flight scale/move operation on a stream can be cancelled and the asset returned to its original placement using the new `$JS.API.STREAM.CANCEL_MOVE` endpoint
- Evacuate endpoints (#8443)
  - The new `$JS.API.SERVER.EVACUATE` endpoint can safely evacuate streams, and any consumers on those streams, from a node
  - The new `$JS.API.STREAM.PEER.EVACUATE.*` endpoint can safely evacuate a peer, and any consumers on that peer, from a stream
  - These operations combined allow for maintenance operations with full transfer of data and state without having to peer-remove first
- Metalayer rescue for disaster recovery (#8408)
  - The new `$JS.API.META.RESCUE` endpoint can temporarily lower the quorum-needed for the metalayer, in order to facilitate the recovery of a system where nodes have been permanently lost and the metalayer cannot reach quorum
- Stream backup and restore v2 (#7882)
  - A new backup format for stream snapshots which reads out per-message rather than per-block
  - The new backup format also now correctly includes non-replicated consumers on follower nodes
- Detect source stream recreation (#8384)
  - The server now detects a source stream being recreated, restarting the sourcing back from the beginning, ensuring new messages are sourced
- Stream source indexing (#8282)
  - Restarts and leader changes previously required expensive backward scans through the stream to find the last sourced indices. These are now persisted in an index for instant lookup.
- Domain-prefixed JS API in system account (#8429)
  - When a system account is bridged between the hub and a leaf node, the domain-prefixed JS API can now be used to operate on the leaf node while directly connected to the hub

###### Changed

JetStream

- Sync changes for replicated streams (#8447)
  - When the `sync_interval` is set to `always`, replicated streams now sync their WAL entries but no longer sync upper stream layer writes
  - The synced log allows the stream to recover safely, but removing unnecessary syncs from the upper stream layer dramatically improves performance
  - Non-replicated R1 streams are not affected by this change and will continue to sync at the stream layer as normal

###### Improved

JetStream

- Shorter wait for durable source/mirror consumer resets (#8323)
  - When using durable consumers for sourcing or mirroring, the heartbeats now short-circuit the recreation backoff

###### Complete Changes
 
https://github.com/nats-io/nats-server/compare/v2.14.5...v2.15.0-preview.1