Windows 8.1 Update has been leaked a while ago, OEMs already got the files for some time too, but today the OEM Letter got leaked along with the MSUs the OEMs got.
You can download the OEM letter to check it out yourself: X1953446LTR.pdf
And the MSUs OEMs got (client and server, x86, x64 and ARM): X19-53446.img (2.10GB)
9600.17031 == RTM!!!
The most important thing in these leaks are of course the MSUs, we’ve had them for some time now, but this new leak confirms the RTM status of the previous leaks. I already posted why build 9600.17031 is RTM before, but that was only circumstantial evidence. All the hashes match, what we got before is exactly the same as what OEMs got!
The OEM letter also confirms that OEMs got both the MSUs and full ISOs (“Windows 8.1 Update GDR” and “Windows 8.1 Update full media release” respectively)
This probably means that MSDN will get updates ISOs too, probably on April 1st or 2nd.
Microsoft has been OneNote a lot lately, making the OneNote desktop app available for free and releasing an OSX version of OneNote (more info on OneNote.com). With Windows 8.1 Update Microsoft is trying to push it even more, they are encouraging OEMs that are preinstalling Windows 8.1 Update on their PCs to bundle the OneNote app with it.
The app will fill in the blank space that appeared on the start screen in the first leak:
Windows 8.1 Update in marketing
According to the OEM Letter the update is a big thing for Microsoft, OEMs need to clearly indicate their devices are running “Windows 8.1 Update”, on their site, on the packaging, in their store etc. They even go so far as to suggest OEMs use it in ads!