Chris Klippel, insider and creator of Rockstar Mag, claims Grand Theft Auto 6 will use the newest version of Rockstar Games' engine called RAGE 9. This engine will be superior to its counterparts and would surprise players with its features.
Klippel mentioned that he himself didn't see the engine in work and just got info from his sources. He also claims that Rockstar Games wants to RAGE 9 to be greater than Unreal Engine 5. If these rumors are true, we are looking forward to the most photorealistic game of the GTA series.