We've put out the release candidate for 17.4 on April 30, 2026, with performance-related options that are part of it.
Lightweight external members is an option for sites with lots of members, who are concerned about concurrency issues on login and registration with members, and are looking to or have out-sourced membership to an external provider. This isn't a quick fix for an issue, but in an architectural advising scenario, it would be good to be aware of the option.
We've added what's currently a configurable option for background processing of content cache rebuilds after schema updates - think updates to document types via Deploy. For larger sites, with lots of content based on the affected document types, this can take a while. By using this option, both the UI and the deploy operations should complete more quickly and be less impacted by timeouts. This could become the default behaviour in the future, but for now, it's an option to be considered for large sites.
We've also added configuration for output caching now, for server-side rendered (template) based sites (it already existed for the Delivery API). This was already possible in Umbraco, but it required custom code, and is now a configurable option. It has some sensible defaults and extension points for handling cache invalidation, so it's more than just a simple time-based cache. We think this could be a quick win for performance and robustness (in the sense of better handling peaks of traffic) for many sites.
Full details are in the release notes and linked documentation and PRs: https://github.com/umbraco/Umbraco-CMS/releases/tag/release-17.4.0-rc