"Kojima Production SUPER CONFIDENTIAL PROJECT's experiment presentation & meeting," Kojima wrote on Twitter today.
The project can't be all that confidential, as Kojima also released a photo of a meeting room where developers had assembled to presumably talk about the new game.
Kojima recently said that he doesn't expect to work on the Metal Gear Solid franchise forever, so it is possible that this project is something outside of his most memorable work.
Metal Gear Solid V: Ground Zeroes launches on March 18, 2014 for Xbox 360, Xbox One, PlayStation 3, and PlayStation 4. The Phantom Pain, which is "hundreds" of times bigger than Ground Zeroes, releases sometime later.