Windows 8.1 Update 1 Leaked
Paul Thurrott and Mary Jo Foley articles:
Short version: There's nothing interesting in the build yet. It will be revelead at Build 2014.
Will it bring more API parity?
Will it be a Service Pack?
When will WinRT==WinPRT (or just WinPRT=WinRT)?
What will it mean for developers?
Will we see some WP8.1 improvements as Cortana or Notification Center?
Will first party apps be updated?