To be specific, I use 1st person for the chapters focusing on Anna Morgenstern and Michael Sharpe. You get to go inside their heads and both see and read things from their direct perspective. For every other character, you'll see them from the outside (no POV images for them) and their thoughts and actions are expressed in 3rd person (and you only get their thoughts if you're not already in a 1st person perspective for someone else).