According to a headline on Konami's official site (opens in new tab) , Metal Gear Solid V: The Phantom Pain and Ground Zeroes will release on Steam. It says exactly that: "Metal Gear Solid V: The Phantom Pain And Ground Zeroes Coming To Steam." On the other side of the link is a 404 page, but we expect the announcement to be made during Konami's livestream in about 30 minutes (11 a.m. PDT, 2 p.m. EDT, 7 p.m. BST).
Not long ago we were saying what a good idea this was . We'll have more as the story develops, and you can watch the livestream below.
UPDATE: Snake? Snake?? SNAAAAA-Oh, there you are! Glad to have you, old pal. As expected, Hideo Kojima made the Steam announcement during the MGS livestream. "I'm really happy you guys are so excited with the cardboard boxes," he said after a demonstration of some new box features. "And yes, it's coming to Steam."
There's no release date announcement yet, but Kojima says that Metal Gear Solid V: Ground Zeroes will, naturally, come first. Also, regarding the box, "You will be able to use it in the game as an item."