Difficulty went up by more than a notch on deity. I feel AI land combat is way better than before (which tbf isnt hard considering it was non-existant), and the teching rate of the AIs is insane. They usually build the first space project around turn 210/220 which isnt bad at all.
Still, i'm pretty sure it's still rather easy to consistently win on deity, at least for science victory as in the end game, you'll probably outproduce and outplay the AI from the key Great Persons. And even the upgrade in land combat AI wont matter once the player gets its hands on artillery and balloons.
Havent finished a game yet though, mostly because of stardew valley stealing my gamer life at the moment.