5.1 focuses on polish, in particular by improving the overall performance of the editor. In addition, this release paves the way for a better, faster, and more secure WordPress with some essential tools for site administrators and developers.
With security and speed in mind, this release introduces WordPress’s first Site Health features. WordPress will start showing notices to administrators of sites that run long-outdated versions of PHP, which is the programming language that powers WordPress.
When you install new plugins, WordPress’s Site Health features will check them against the version of PHP you’re running. If the plugin requires a version that won’t work with your site, WordPress will keep you from installing that plugin.
Introduced in WordPress 5.0, the new Gutenberg block editor continues to improve. Most significantly, WordPress 5.1 includes solid performance improvements within the editor. The editor should feel a little quicker to start, and typing should feel smoother.
Expect more performance improvements in the next couple of releases.