After doing all the hotlap events, I'm now working through the quick race events.
Experience with AI is mixed...
They don't seem to want to overtake each other on the straights.
They are very aggressive if you get along side them in to a corner... and will do almost anything to try and stop you passing them, including punting.
They have 'magical' exit speed in the more powerful cars - eg; I ran the C9 at Spa event. The car has zero grip in low gears when the turbo spools up, yet the AI fly out of the final chicane and the 1st corner with unbelievable grip.
They brake on corner exits, yet don't lose any speed - noticed this a few times last night... RSR at Monza, where AI brake lights come on out of lesmo 2 & parabolica, yet no speed loss. And 918 at Barcelona, medium speed blind right over crest, braking on exit kerb, yet no loss of speed.
They are immune to contact - they touch you, you spin. You touch them, they carry on unaffected (and you spin).
Still, they are MUCH better than any version of GT.