The PHP.net site has officially announced the latest (and final) Release Candidate for the upcoming PHP 7.1.x release: PHP 7.1.0 RC 6:

The PHP development team announces the immediate availability of PHP 7.1.0 Release Candidate 6. This release is the sixth and final 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 with the other Release Candidates you can grab the source download if this release from this QA site or the Windows binaries from the Windows QA site.