The php.net site has posted an announcement about the latest Release Candidate for the PHP 7.1.x series: PHP 7.1.0 RC 3:
The PHP development team announces the immediate availability of PHP 7.1.0 Release Candidate 3. This release is the third release candidate for 7.1.0. All users of PHP are encouraged to test this version carefully, and report any bugs and incompatibilities in the bug tracking system.
[...] For more information on the new features and other changes, you can read the NEWS file, or the UPGRADING file for a complete list of upgrading notes. These files can also be found in the release archive.
As a reminder, this is a preview release and is NOT designed to be used in production . The release schedule is provided on the wiki, the next Release Candidate will be coming in early October (the 10th) with three more following. The target release date for PHP 7.1.0 is sometime in the later part of November.