Recently Rockstar along with Take Two filed a trademark for Hangar 13 which leads us to believe that Rockstar could be at work on a new game. While Rockstar will be developing GTA 6 we think that Hangar 13 may arrive first.
We have heard talk about Hangar 13 being an add-on for GTA 5 by way of a DLC and this could be a follow up to UFO secrets that have been hidden inside GTA 5.
There was also talk going around that Hangar 13 would be a rebranding of Agent, a game that was revealed in 2009 before then fading away. The Agent trademark has been renewed last year.
Rockstar have only recently filed the petition for Hangar 13 and this means that we are not very likely to hear anything about the game anytime soon.