We know he's a replicant, but I don't think he knows with any confidence: all he knows is that Gaff has an uncanny degree of insight, and that a definite replicant thought he was a man and spared his life to share the end of his own life with him. So he faces even more puzzles than them: if he isn't human then he had less free will than the other replicants since then he was created to unquestioningly retire them. Is he now going to enjoy that freedom and flee with Rachel, since he "owes her one", does he even know what his plan is as the lift doors shut?