Another leak from WZT here.
This is the RTM for the Windows 8.1 Core Single Language.
These are used in laptop installs, and it should let you activate using your CSL OEM key. First you upgrade using the default key, then you change it with Admin Command Prompt commands:
SLMGR /IPK XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
SLMGR /ATO (if ATO online activation doesn't work, use phone)
SLUI 4 (phone activation)
There's currently no KMS activation, so don't use gVLK until some KMS v6 servers come online or someone comes out with a KMS activator. It could be days or months. I don't know, so don't ask.