It’s only just begin development, though.
Grand Theft Auto V launched in 2013 on the Xbox 360 and PlayStation 3, followed by a 2014 release on PS4 and Xbox One, and a 2015 one on PC. It went on to become the highest selling game of all time– so it should not come as a shock to anyone that Rockstar are already working on a sequel. Apparently, Grand Theft Auto VI is now in development.
That said, it seems to be very early in development- so much so that, as of right now, even a location has not been decided for the game yet. At some point, Rockstar did consider developing a Grand Theft Auto Tokyo, but the idea was given up on, with Japan’s clogged road system being the major deterrent.
Of course, if all of this information is true, then Grand Theft Auto VI is years away from release- the earliest we would see it is probably 2018 or 2019. In the meanwhile, it is likely Rockstar has something else in the works- perhaps a Red Dead 3 that we might finally see announced this year?