Yesterday, one of my desktops offered Windows Update KB2976978, Compatibility update for Windows 8.1 and Windows 8. This pc was purchased with Windows 8 on it and upgraded to Windows 8.1. KB2976978 installed without any problem.
Compatibility update for Windows 8.1 and Windows 8
My other desktop started out as a Windows 7, was upgraded to Windows 8, then Windows 8.1 and already had that update installed, back on August 18, 2014. I figure it was probably installed to make it compatible with Windows 8 at that time.
Is this new offering of KB2976978 possibly getting pc's ready for Windows 10 installation?