---
prelude: |
    The ``OpenStack 2026.1`` (``Watcher 16.0.0``) release brings significant
    improvements to the execution of strategies, reliability, and testing
    infrastructure. This release focuses on enhancing the robustness of
    action plan management and expanding test coverage for critical migration
    functionality.

    The Applier service now supports experimental native threading mode,
    completing the transition across all three core Watcher services. With API,
    Decision Engine, and Applier all supporting native threading as an
    alternative to Eventlet, this release marks a significant milestone in
    eventlet removal initiative. Native threading remains disabled by default
    and is not recommended for production use.

    The codebase has been modernized through migration from novaclient to
    openstacksdk, aligning with OpenStack's standard client library approach
    and improving long-term maintainability.

    There are updates to supported datasources.
    The Prometheus datasource is deprecated in favor of Aetos.
    Also, the Monasca datasource, that was deprecated in 2025.1, has been
    fully removed from codebase.

    Other key highlights include homogenized action plan cancellation behavior
    across threading and eventlet modes, providing more consistent and
    reliable operation. The release also enables comprehensive zone migration
    testing, improving quality assurance for multi-zone deployments.

    Additionally, critical bug fixes ensure proper migration notification
    handling and enhanced monitoring capabilities with the addition of service
    monitors for the Applier service, making Watcher deployments more
    observable and maintainable.