WordPress 5.1 “Betty” was released on February 21, 2019.

WordPress 5.1 will be the first major release of 2019, including PHP version upgrade notices, and block editor improvements.
Near the end of the month, WordPress 5.1 was released, featuring significant stability and performance enhancements as well as the first of the Site Health mechanisms that are in active development. Most prominent is the new warning for sites running long-outdated versions of PHP.