Microsoft is still on target for the Windows 8.1 end of August release to manufacturing but Microsoft is not planning to make Windows 8.1 available to TechNet and MSDN subscribers until after the RTMs hit. Microsoft is planning to delay the Generally Available date (and official launch date) of Windows 8.1 until sometime in the middle of October.
This delay gives Microsoft some extra time to exterminate bugs still lingering in the OS. It also gives Microsoft time to plan for a bang up launch. Finally, partners will benefit because they’ll have extra time to finalize testing with drivers before the October hit date.
Windows 8.1 build (9471) leaked over the weekend and includes a wealth of features. And although the build isn’t an RTM-escrow, it is basically feature finished. The differences between this build and 9471 will be pretty small.