I read on ZDnet that Microsoft will first release Windows 8.1 to computer manufacturers (RTM) in August but we have to wait till October 2013 to get the final version.
Mary Jo Foley: "One of my best tipsters tells me, Microsoft is going to hold off on making available the final Windows 8.1 bits until mid-October 2013 or so. That will be both the general availability date, as well as the "launch" date when new hardware running those bits will be available."