In summary: (spoilers ahead)

AI created -> AI becomes monk, this is good AI -> bad AI also created, controlled by single mastermind AI -> bad AI kill humans -> Overwatch created -> good AI sacrifices herself to free other AI from bad AI mind control, thus becoming AI Jesus -> AI now have free will. Some become good, some stay bad. -> optimistic because AI Jesus saved humanity from being killed and now Overwatch is winning the war against bad AI

That's about it.