Will the AI ever surrender?

It is possible but the threshold must be real high. In the game I am playing, the AI just surrendered. Like you I had taken their homeworld, destroyed most of their fleet, and conquered all but one of their colonies. The last colony turned out to be a tiny Intel site. They couldn't maintain a single ship in space. They had no defense.

But I had to bring them to that point. They must have refused to surrender a half dozen times before. As long as they could support a ship, they denied me.

The default amount for the AI to accept surrender is 500% plus there is a 25% they won't accept even if the score difference is more than that.

I haven't checked to see if some Empires have higher thresholds in their script files.

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I had a score of over 30 million, compared to the Cue Cappa's ~1.5 million, and they refused to surrender.

Then I installed 1.13 patch and the savegame wouldn't load.

I guess Cue Cappa's save-game sabotage strategy worked on you.

Yeah, patches tend to hose save files. I don't really know here, I've ever seen them surrender either.

I think the score difference is 500% across the board.

Something must be wrong. I haven't seen a surrender in recent memory which is much lower than 25%. Haven't seen any similar problems in SE4.

So 500% more ships (by number?), 500% more units, 500% more research, 500% more intel? yeesh...

500% more score in comparison 'your race' - 'other race'

I just remember the thing, when i almost defeat Norak, and only 2 planets left to conquer , they surrendered to another race =\
is it fair?

Nope, but they hate you thus they surrender to whoever they like most.

They are too stupid. They had surrendered to the race i am in war with. So i just continued my conquest. Instead of that they can surrender to the race, which have treaties with me. That way i would be unable to get this last planet.

ah, yes. that was quite stupid.