The currently required minimal PHP version is still 5.2.4+.
The recommended version is 7. According to archive.org since December 2, 2016.
Note that many plugins and themes need at least PHP 5.4 or newer nowadays, and that PHP versions below 5.6 do not get security updates anymore and are therefore probably not safe for production.
WordPress doesn’t use any of the newer PHP features, but it does work with the latest PHP version.