This is release 4.9.0-alpha1 of the Authoritative Server. It brings a few new features, and a collection of small improvements and fixes. Some internals have been reworked to support the new features. A detailed list of changes can be found in the changelog.
Please make sure to read the Upgrade Notes before upgrading.
If you install (not upgrade to) this version on Debian or Ubuntu, please read this ticket about broken configs first.