A former Rockstar India employee has listed Grand Theft Auto 6 as one of their projects on their resume. If true, this means that GTA 6 is currently in development.
Bibin Michael, who's worked as an artist on GTA 5, Red Dead Redemption 2, and Forza Horizon, listed GTA 6 as one of their projects on the professional artist portfolio site Art Station. Though the mention of GTA 6 has since been deleted, VG247 reported that it was at one point listed on Michael's Art Station account.
Michael apparently worked on vehicles for GTA 5 DLC and GTA 6 between December 2017 and April 2018, the same period he listed as working for Rockstar India on LinkedIn. Furthermore, Michael's name appears in Red Dead Redemption 2's Thank You page which lists developers who worked on Red Dead Redemption 2, but wasn't part of the core team, or part of the team when the game shipped.
Employees have accidentally leaked projects via their resumes in the past. There's also the chance that the listing was made in error and so it's hardly a confirmation. Still, considering how successful GTA 5 has been for Rockstar, there's bound to be a GTA 6 sometime in the future. Whether that's in a couple of years from now, or a decade from now remains to be seen.
In the meantime, Rockstar is currently working on the Red Dead Online beta and there are still regular updates to GTA Online. Check out our Red Dead Online guide for more coverage on Rockstar's online western.