The official PHP.net site has posted an announcement about the latest release in the PHP 7.3.0 pre-release cycle: PHP 7.3.0 alpha 1.
PHP team is glad to announce the release of the first PHP 7.3.0 version, PHP 7.3.0 Alpha 1. This starts the PHP 7.3 release cycle, the rough outline of which is specified in the PHP Wiki. For source downloads of PHP 7.3.0 Alpha 1 please visit the download page.
Please carefully test this version and report any issues found in the bug reporting system. Please DO NOT use this version in production, it is an early test version.