Windows 8.1 Update & Windows Server 2012 R2 Update Is Available On MSDN

The update formerly known as Windows 8.1 Update 1 is available on MSDN now as a slipstreamed build called Windows 8.1 with Update

There is also something called Windows 8.1 Industry Update that appears to be the non-slipstreamed update for existing installs.

Some may have forgotten, but Windows desktop and server share the same code base, even if they live in different groups within the org chart in Microsoft. Windows Server 2012 with Update is also available on MSDN:

The Windows 8.1 non-slipstreamed update should also install on existing WS2012 R2 installations.

I was told by Kirill Andrienko that the ill-fated TechNet also has the updates.