When build 17031 was uploaded to Microsoft's Windows Update servers and people found a way to update through tweaking settings in the registry, Microsoft pulled it. It may have merely been a test.
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Microsoft has confirmed that Windows Server 2012 R2 will also be getting a "Spring Update" around the same time as Windows 8.1 but the company has yet to offer any specifics.
Microsoft has now officially announced the update to Windows 8.1 which will arrive in the Spring. The update adds a ton of features for mouse and keyboard users with modern apps.
Screenshots of a reported build of the Windows 8.1 spring update have leaked but they do not show too much, other than a small update to IE11 and of course, the build number.