The Ehcache 3.x line is currently the development line.
For more information, you might want to go check the wiki.
Getting started with the new API
For samples, documentation, and usage information, please see http://ehcache.org.
We released 3.2.0 on December 12th 2016.
The release notes contain the links to the artifacts and the documentation to help you get started.
You should consider upgrading to 3.2.x as it does all 3.0.x and 3.1.x do and more with a fully compatible API. The only thing to note cmopared to 3.0.x is that transactional support has been moved to a separate jar.
Current development & next release
We are still working on the missing features of the clustering tier of Ehcache 3 which will be included in upcoming releases. We may still do 3.1.x release to include all fixes that have been made on it, but this is now less a priority. There is no longer any plan for a 3.0.x release.
See the milestones on GitHub for more details on the current status.