Found another reference to Windows Phone 8.1

It is on the "Preview for Developers" app the Microsoft publishes, which I'm sure that we are all familiar with.

http://www.windowsphone.com/en-us/store/app/preview-for-developers/178ac8a1-6519-4a0b-960c-038393741e96

Dqjrfd9_medium

via i.imgur.com