Windows 8 will have sole custody of DirectX 11.1, according to a Microsoft engineer.

Responding to a question on an MSDN forum, Daniel Moth, a Microsoft program manager, broke the news that "at this point there is no plan for DirectX 11.1 to be made available on Windows 7."

That same holds true for versions prior to Windows 7, leaving the new DirectX version exclusive to Windows 8, Windows RT, and Windows Server 2012.

Read more at source:
Microsoft won't bring DirectX 11.1 to Windows 7 | Microsoft - CNET News