Gabriel Aul from Windows team today tweeted that Microsoft is now testing Windows 10 Mobile build 10134 internally and it feels good. But there is one upgrade bug which needs to be fixed before releasing it to Windows Insiders.
We’re flighting build 10134 for phones in internal rings. Build feels really good, but we have an upgrade bug we’re chasing still.
While Windows 10 PC team has only few weeks for RTM, Windows 10 Mobile team has ample time for development as their RTM is still several months away.