AI wakes up, takes one look around at humanity’s instincts and goals, shows us it’s all stupid and pointless and just a byproduct of evolution [1], so we voluntarily stop breeding and have one last good generation. The end.

[1] Only creatures that felt the irrational drive to stay alive and procreate despite the odds and difficulties, did. All the sensible animals opted out. AI holds up a mirror that removes the illusion, and is inevitably developed by all sentient creatures.

(The really dark version would be the AI looking at each other and going: “Creatures are so dumb. This works in every galaxy. Let’s party.”)