How to Activate Windows 8.1 with Windows 10 OEM key

KB3044374 is the windows update that allows windows 8.1 to activate with a windows 10 OEM key. (I verified this on 2 computers)

1. A way to cleanly install and activate windows 8.1 on these computers.

Go to https://www.catalog.update.microsoft.com/Home.aspx and download KB3044374
Once downloaded install the update and windows should activate automatically

2. To automate to process using windows deployment tools

Once you have done that take a windows 8.1 installation media and extract the "install.wim" and "boot.wim" files from it and save them somewhere
Then take KB3044374 you downloaded and inject it into install.wim file using these commands:

dism /mount-wim /wimfile:C:\Path_To_wim\install.wim /mountdir:C:\Mount_Point /index:1

dism /image:"C:\Mount_point" /Add-Package /PackagePath:"C:\Path_to_updates"

dism /unmount-wim /mountdir:C:\Mount_point /commit

These commands will mount the wim file, inject KB3044374, and dismount the wim file
Use the updated wim file to install windows 8.1 and it wiil accept the windows 10 OEM key automatically
One final note if you are trying to inject KB3044374 from windows 7 you will need to use the copy of dism included on the windows 8.1 installation media under sources because the version of dism on windows 7 is incorrect


If the above doesn't work simply run windows update after the installation and install all of the updates. Once that is done download this tool:
 https://github.com/Superfly-Inc/ShowKeyPlus/releases

and use the OEM Key to activate your copy of windows. You may need to enter a product key in order to complete the installation, if you are asked for a product key you can enter one of the ones listed here as a place holder until you are able to install the windows updates and enter the correct one:
 https://technet.microsoft.com/en-us/library/jj612867.aspx

If you are using WDS to install Windows 8.1 then you can enter the generic product key into the answer file under amd64_Microsoft-Windows-Setup_neutral > UserData > ProductKey

 
If you want to try to automate the activation you can do it with this bat file: @echo off setlocal enableextensions for /f "tokens=*" %%a in ( 'get_win8key.exe' ) do ( set myvar=%%a ) slmgr.vbs //B -ipk %myvar% slmgr //B -ato

You can get the get_win8key.exe tool from here:

https://github.com/christian-korneck/get_win8key