According to Rockstar, the recommended specifications are based on hardware that can run the game at 1080p, at 60 frames-per-second. For that, Rockstar suggest a Nvidia GTX 660 2GB or AMD HD7870 2GB.
"To run the game on a 4K display at 30fps, you’ll need at minimum an AMD HD 7870 or Nvidia GTX 760 with 2GB of VRAM." As for the 4K at 60 frames-per-second, that'll require a "high-end SLI or Crossfire setup."