KDE has announced the Release Candidate of the 4.13 versions of Applications
and Development Platform. With API, dependency and feature freezes in place,
the focus is now on fixing bugs and further polishing. We kindly request your
assistance  with finding and fixing issues.
A partial list of improvements can be found in the 4.13 Feature Plan . A
more complete list of the improvements and changes will be available for the
final release in the middle of April.
This release candidate release needs a thorough testing in order to improve
quality and user experience. A variety of actual users is essential to
maintaining high KDE quality, because developers cannot possibly test every
configuration. User assistance helps find bugs early so they can be squashed
before the final release. Please join the 4.13 team's release effort by
installing the release candidate and reporting any bugs . Read this article
 to find out how you can help testing.
The official announcement  has information about how to install the RCs.