According to an article on MTV, Grand Theft Auto IV will use the RAGE graphics engine - the same engine which was used in "Rockstar Games Presents TableTennis."
"[In a recent interview about Table Tennis, a new game from Rockstar,] the Rockstar reps explained that the game was running on RAGE, the Rockstar Advanced Game Engine. This is the graphics technology gamers are to expect from future Rockstar games, including the next GTA."
We'll try to get confirmation on this shortly, but for now head over to www.rockstargames.com/tabletennis/ where you can find screens and movies of the game which show off the RAGE graphics. Perhaps this can give us an idea of what to expect in GTA IV?
And in other news.. according to Janco Partners analyst Mike Hickey, a financial consultant for Take2 Interactive, around 150 developers are currently working on the development of Grand Theft Auto IV. Thanks to PlanetGTA for this one.