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# AI 3.8-15.1.4 Release Notes

## Summary

### Major Enhancements

* [**S3 proxy mode**](/ee-ai-en/ai-3.8-15.1.x/data-access/s3-api.md#pattern-b-load-balancer-proxy-mode) **zero-copy reads** improve segmented-read efficiency in proxy-mode deployments.
* **FUSE stream locking improvements** reduce contention in the FUSE stream path.
* **Longer Netty close timeout defaults** reduce premature connection closure during busy or slow shutdown paths.

### Bug Fixes

* **S3 write cache list behavior** is fixed for deployments affected by the earlier schema change.
* **Write-cache metadata handling** is corrected so filenames containing spaces no longer risk metadata corruption in write-cache deployments that use FDB metadata.
* **FUSE directory listings** no longer show ghost entries caused by an FDB pagination bug.
* **UFS multipart upload buffer leaks** are fixed.
* **A Netty channel deadlock** under very high write concurrency is fixed.

## Breaking Changes

* **Only deployments with S3 write cache enabled are affected.** For those deployments, the FDB metadata encoding changed in this release. If you are upgrading from `15.1.3` or earlier, existing metadata must be migrated before or during upgrade.

## Upgrade Notes

* Only deployments with S3 write cache enabled need to take action. If you are upgrading from `15.1.3` or earlier, an FDB metadata migration is required.
* Complete any pending writes and make sure the cluster is stable before starting the upgrade.
* Do not plan on downgrading to `15.1.3` or earlier after migration unless you also restore a pre-upgrade FDB backup.