Thanks @decastell -- I'm pretty sure you're right about Anton. I remember the scene at the end where Vincent beats Anton and saves him; it was a very satisfying climax. Maybe Vincent is Steadfast which makes Anton a Change IC?
That said, I seem to recall that Anton isn't present for a lot of the story, so I wonder if there is a hand-off somewhere. I know Eugene (Jude Law) starts off challenging Vincent a lot ... I found this quote:
I'm sure you're sincere...but I was being groomed for something like this myself. Even without the accident I don't think I would have made it. My point is--how the hell do you expect to pull this off?
But then I was confused because later in the story, Eugene is actually pushing Vincent towards his dream to overcome his genetics:
Anyway, you don't have a choice. You run, you may as well sign a confession, turn us both in right now.
I guess it bears more analysis! It's been a while since I saw it, so maybe Anton is actually present more than I recall.