The title says it all. I was playing on a Huge Multi Random, had made allies with one guy because he was shooting off superweapons like nothing else, and was hostile to the other three players in my galaxy. I found a couple good choke points, double starbase and titan in the middle one, and then researched the win the game tech. (On that note I feel like its way too easy to get there) I sat there, waiting for every single AI to come screaming at me in one massive rush, but instead....I never faced a single opponent. They just never registered that I was about to win. At the very least I'd expect the superweapon guy to break our alliance to attack me, but not even that. And I didn't have allied victory on, so he wasn't going to win by letting me research it. 

tl;dr AI doesn't recognize that you're about to win thru tech research, fails to attack to stop said research.