If you are willing to make a few tweaks to your registry, you can get Windows 8.1 update 1 right now. By adding a value to your registry, this will give you access to download and will get you the bits right now, without accessing any third-party.
Several users have reported that the method is working and have successfully downloaded the update. The current thought is that by tweaking the registry, it mimics your machine to be that of a user who is dogfooding the update and then sends the bits to your machine.
In regedit, navigate to “HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\” and create a new key called “SHWindowsPoolS14″, now reboot your PC and check for new updates. You should see “Update for Windows 8.1 for x64-based Systems (KB2919442) – (S14 Prerequisite v01.0008)“, this is the first in a series of updates that will update your PC to Windows 8.1.1 (or whatever it’s called).