Alex Garland always made a great point about the Ex Machina ending: The part Ava *truly* turns on Caleb is when he gives a weak, shrugging, ambiguous answer to her: “Will I get switched off?” question during one of their sessions.
She realizes at that moment: He’s playing both sides. He doesn’t value her life. So why should she value his?
You notice it when you watch the scene: She drops the “lovesick girl” act and gets genuinely annoyed at him and his indifference.
Like, she was using him to get out of there. All along. But if his answer had been different, if he’d been outraged and said “No, it is absolutely wrong to do that to you!”…eh, I think she might have taken him with her at the end.