The AI seem to be lacking in Rebellion but this has been bought up a few times already. I played a game against 3 hard AI and only one of them attacked me throughout the 3-4 hour game and even then it was with a handful of ships and no capitals. They did start to spam the Novalith eventually but their fleets remained small and scattered.
I decided to up the difficulty to see if that would help, it did and it didn't, on unfair 1v1 they never attacked me, not once, they didn't build any Novaliths nor did they build any communication things to spread culture or star bases. They maxed out their capital ship cap so they had 11 cap ships they they trained to rank 3 but they built nothing else, just the capital ships. I sent in a titan and just did hit and runs till they were all dead as they never chased me, they just kept returning to one of their planets where their titan was kept.
Also the AI's tendency to run away like they normally do when confronted with a larger enemy fleet seems to be even more prevalent, I had a fleet of 20 corvettes and a capital ships and an enemy fleet of about 20 frigates, 5 missile frigates and 2 capital ships legged it, unless their fleet was about 3 times the size of mine they would never engage me.
Also there is the issue with AI not using titans but that has been mentioned in the forums multiple times.
So far I am enjoying it despite the issues but that's what a Beta is for. Look forward to full release, good work guys.