The main PHP.net page has posted an announcement about the latest Release Candidate in the PHP 7.1.x series being tagged and released: PHP 7.1.0 Release Candidate 5:

The PHP development team announces the immediate availability of PHP 7.1.0 Release Candidate 5. This release is the fifth 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 release candidate and is not to be used in production. You can download and test out this latest release from the PHP.net source QA site or the Windows QA site for the binaries. The next release candidate for this version will be released on November 10th with a goal of a final release following that.