Windows RT devices, such as the Surface RT and the Surface 2, won't get an upgrade to Windows 10, but instead Microsoft has been working on a platform update that brings the original Start Menu which the company introduced in the first Windows 10 builds. This means that it is technologically based on DirectUI, instead of an XAML-based menu which shipped with the RTM PC version of Windows 10. Aside from the Start Menu, the update is expected to include some minor tweaks and performance improvements as well.

http://tech.slashdot.org/story/15/09...-to-windows-rt