The M Developer Preview runs from May 27 until the final Android M SDK, which we’ll release shortly before the public release during Q3 2015.
At key development milestones, we’ll deliver updates for your test devices. The tentative milestones are
Preview 1 (initial Preview release, late May),
Preview 2 (late June/early July), and
Preview 3 (near final, late July)
These updates culminate in the final SDK (later in Q3), which delivers the official APIs for the new version of Android, as well as the final system behaviors and features.