Tenet ending explained · Cinespective

What happens

The team stops the algorithm, Kat kills Sator, and Neil sacrifices himself. The Protagonist realises he built the Tenet organisation, so the mission that recruited him was his own design all along.

The last image

The Protagonist parts from Kat, then goes on alone, still protecting a world that will never know what he did.

What it says

The ending answers the film's question about free will: events may be fixed, but acting still matters. The Protagonist trusts a mission he cannot fully see, and the film asks you to accept that this faith is what makes the choice meaningful.