By now, there is little doubt that Rockstar is actually working on ‘GTA VI’, having already foreseen that their current project ‘Red Dead Redemption 2’ will probably not go the same way as GTA V once did.
The development of the game is mentioned by the 3D artist Bibin Michael in his summary on his own homepage ( now removed ). It said that he had been working on the “upcoming GTA VI” between September 2017 and April 2018, suggesting that the development of the game has been going on for quite some time.
That Bibin Michael has actually worked for Rockstar is additionally confirmed by the credits in Red Dead Redemption 2, where he is listed in full name. In this respect, one can probably assume that his personal CV is also correct, in which he speaks on top of that separately from GTA V and GTA VI in his sentence, which is likely to exclude a mistake or a mistake.
Believing recent rumors, GTA VI will, however, appear only in the next generation and is even there as a time-exclusive title on the PS5. If that’s true, even the timeframe might fit, since the launch of the PS5 is expected in late 2020. Then the game would be at least three years in development.