Rockstar has not yet announced GTA 6, but, according to the former artist of the studio, is already working on the game.
What is known
Michael Bibin updated the page on ArtStation,adding a new job and another project to his list of achievements. Michael currently works at Codemasters, drawing cars for GRID and F1, but until April 2018 he worked at Rockstar India, where he created car models for GTA 5 and GTA 6. Michael's name is also on the list of developers for Red Dead Redemption 2.
At the same time, the artist’s profile on LinkedIn is deprivedinformation about the projects in which he participated. Rockstar monitors leaks and does not allow employees to talk about projects, so mentioning GTA 6 could be considered a violation of the contract. Also note that in January 2019, the Indian division was looking for a “car artist,” and Michael may have been the reason for the lack of personnel.
Rockstar is famous for being slowin game development, so you shouldn’t expect a quick release of GTA 6. Games about the great car thief are usually made by Rockstar North, and work on the western RDR 2 is given to the division in San Diego. The preparatory processes are being taken over by smaller studios, and it looks like the India office has already started creating some of the environment details.