I've played a game versus 8 hard AIs, when I took theplanet for ocupation victory 4 of them were still alive. So Can't say if harder AIs will do better. Anyway, hard AI is far less difficult at the moment than in Diplomacy still (or I have gotten way better Oo).
In the 30 minutes I needed to win the game, none of the AIs moved and attacked the planet, which is rather boring.
For the Capital Victory at least AI seems to be working, as they always retreat the Cap if it is attacked.