Has anyone noticed any ai improvements in 1.3?

Copy and paste the same message will not make it more ( or less) true, bottom line is AI is pretty much exactly as in 1.2.

Same here, 99.5% against AI, I also like the AI in R3E, maybe a little better, but still enjoy AC AI tremendously. If different than 1.2, it is minor, a few tweaks here and there, for the better.
I raced the GT3's at Zandvoort before and after 1.3 and the only major difference was that it was more pleasant to drive my own car on the V5 tyres.

I suggest to redo the AI fast lane on the mod track that the AI is terrible, it worked for me every time. The tell sign of the old AI fast lane is when they start badly, hitting each other, and then drive following each other.
Like you I wish they would drive closer to each other when side by side , rather than each at edge of the track.

 

The overall behaivor might be the same like in 1.2, but I think they got some problems with the new pyhsics. I did some races at Nordschleife and Spa with GT3 cars and I have to say that they go of track more often and especially at Nordschleife's first corner they sometimes totally miss the braking point and then heavily crash into the barrier. I also noticed Huracan Ai drivers to break to late and kick of some other cars at other tracks more than once.

 

The GT cars were doing this in 1.2 as well, I couldn't do 4 laps on Nords Endurance without 5-8 AI cars crashing and quitting.