Metal Gear Solid 5 is a combination of The Phantom Pain and Ground Zero
Metal Gear Solid 5 is official. Furthermore, it's a combination of both the recently teased The Phantom Pain and Metal Gear Solid: Ground Zeroes, developer Hideo Kojima revealed at a panel during the Game Developers Conference.
A new trailer for the mysterious game, compiled of footage from both games, also showed off the studio's new FOX engine. The gameplay demo showed Snake awakening from a coma after nine years and escaping a facility filled with enemies. Because of the coma, Snake's movement is limited. The Phantom Pain will serve as the early prologue of the game and will be linear. Later on, during the Ground Zeroes part, gameplay will shift into a more open-world environment. Below is the lengthy trailer that hopefully gives you a better idea of the game.
It's also important to note that Metal Gear Solid 5 is a continuation of Metal Gear Solid 3, the PSP titles, and Peace Walker. Platforms were not announced, but the game was running off a high-end PC, so I'm going to assume next-gen consoles is a safe bet.