This post is also available in the TechNet Wiki:

http://social.technet.microsoft.com/wiki/contents/articles/16401.how-to-check-if-a-rdp-connection-is-using-rdp-8-x.aspx

To verify if a connection from a remote computer that is running Windows 7 SP1  to a Windows Server 2012 (R2) backend with the RDP 8.x client you can follow  these steps:

– Connect to Remote Desktop Services back-end offering RDP  8.0 (Windows Server 2012/2012 R2 or a Windows 8/8.1 VDI)

– Click on the connection quality button (looks like a wifi icon)

– If the information dialog that appears says “The quality of the connection to the remote computer is excellent and UDP is enabled” then the connection is using RDP 8.x