Yes there were some API changes recently which in our eyes makes XTK much easier to use.
To avoid breaking existing projects, we decided to skip the releases for a while.
There are currently three important files:
http://get.goxtk.com/xtk.js - The latest stable XTK release which links at the moment to xtk_release4.js
http://get.goxtk.com/xtk_release4.js - XTK release 4 using the old API
http://get.goxtk.com/xtk_edge.js - The current master of XTK using the new API
For new developments, one should use xtk_edge.js to interface the new API. This release is also stable and ready to use.
To be safe to not break existing old code in the future, it is recommended to use xtk_release4.js instead of xtk.js since we will switch the xtk.js link to the new API in the future.
On July 12th or August 12th we will switch xtk.js to the new API when performing a new release.
The current API documentation is here: http://api.goxtk.com/renderer3D.html