Facebook developers have released HHVM 3.21 as their alternate PHP implementation that also powers their Hack programming language. HHVM 3.21 is a long-term support release that will make it maintained for nearly one year.

HHVM 3.21 features a number of improvements for PHP 7 code compatibility, void is now supported as a return type in PHP7 mode, support for the libsodium extension for modern crypto as being introduced in PHP 7.2, improved IDE auto-completion support, and other features and fixes.

PHP/Hack developers interested in more details on HHVM 3.21 can find all the useful information via HHVM.com.