The HHVM project has made an announcement on their site about the latest update for the PHP language processor, v3.24 and how, among the list of changes, they're completely dropping support for PHP 5.
HHVM 3.24 is released! This release contains new features, bug fixes, performance improvements, and supporting work for future improvements. [...] 3.24 is the final release targeting PHP5; this includes source-level compatibility for PHP5 extensions (ext_zend_compat). We recommend migrating to Hack or PHP7.
As 3.24 is supported though 2018-12-17, this means that support will end at roughly the same time as PHP5 itself is scheduled to become unsupported (2018-12-31).
Other updates in the release include the retiring of support for Debian 7 Wheezy and Ubuntu 17.04 Zesty, the inclusion of "using" blocks and the addition of the XHP Attribute Spread Operator. You can find out complete details about this release from the HHVM blog.