SPS almost seems more likely than mirrors at this point.

by uberfoop , Seattle-ish, Friday, February 15, 2013, 10:45 (4299 days ago) @ bluerunner

Real-time reflections made their way into Halo 1, but then vanished forever because Bungie realized that they were kind of expensive. Seems like Bungie toyed with the idea for Halo 3, but it didn't make it into the final game. (Frankie once suggested in a bulletin that it's still there for visors and such in Halo 3's SP, but as far as I can tell that's full of crap. The game has a somewhat neat system for transitioning between regions with their own baked cubemaps, but that's it.)