Kohana has two different versions to choose from. All versions are supported for one year from the release date.
Current stable release of the 3.3.x series, this is the recommended version for all new projects. Support will last until November, 2013.
Officially supported maintenance version. Support will last until May, 2013.
You can find unsupported versions of Kohana in the 3.x archives or 2.x archives.