UPDATE 25/08/2015 5.26pm: It looks like all the Phantom Pain streams have been removed, likely due to Konami shutting them down.
ORIGINAL STORY 25/08/2015 4.08pm: Metal Gear Solid 5: The Phantom Pain is not due to be released until next week, but owners of early copies are already beginning to stream their gameplay online.
Kojima's final MGS title has a street date of Tuesday 1st September, although review copies are out in the wild.
Eurogamer spotted this Twitch stream below, for example.
Beware of spoilers, naturally: