Contrary to initial reports, Konami has confirmed that Ground Zeroes and Phantom Pain are indeed separate games. Here's how Kojima himself is describing it:
"Ground Zeroes" is a prologue of "MGSV". 9 years after that event will be "The Phantom Pain"....
It has been almost five years since Metal Gear Solid 4: Guns of the Patriots was released back in 2008, and over a year since Metal Gear Solid: Ground Zeroes was announced to the public. So when Hideo Kojima took the stage at GDC in San Francisco today...