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Most of the speculation is that it will be sometime this spring. Google has introduced new versions of Android at Google I/O in the past, and there was leaked material from Qualcomm that suggested a spring 2013 release as well. Assuming that is correct, and of course it may not be, it will still take some time until you see 5.0 "in the wild". I would be surprised if devices running 5.0 are widely available before fall.