The Windows 8.1 Spring update has reportedly reached RTM at build 17031 and has already been handed over to OEMs according to WZor



From Neowin:

Microsoft announced the "Spring Update" (their words, not ours) just over a week ago at the Mobile World Conference, and said it would be made available through Windows Update at the beginning of April. And for lack of an official name for this update, we asked readers what they think the update should be called, so if you haven't cast your vote yet be sure to make your opinion count.

  Windows 8.1 Spring update reportedly signed off to RTM