It received v.1.01 at launch (changing game core version from 1.2.2 to 1.3.7 and add intercontinental DLC,what was free for preorders)
Then the 1.02 hotfix fixing cars livery editor
And last in middle-end of July the 1.03 with performance improvements,new FFB settings to suit console feeling and ability to pay for dedicated private servers (trough external servers hosts websites)
Still good Amount to bugs and issues to fix..like headlights beam issue, some wheel compatibility, save file that get corrupt in championship mode, having more than 150 friends on PSN make crash the game in multiplayer.
That are the "big ones" ...then you have minor issues and bugs like trophies that don't unlock, lap counter bugged, AI in some starts need tweaking ,etc,etc.
Performance on PS4 Pro is really nice now in 4K or supersampling in 1080p (if you don't have a T500 wheel) getting around 50-60fps (in normal 1080p with better graphics details it's as standard PS4 performance )
On standard PS4 it goes from 30-45fps
Great SIM that needs some work done, now in September there will be 1 or 2 updates bringing the GT4 DLC and game core version moving forward from 1.3.7 to 1.5.x (and hopefully bringing some bug and issues fixes)