I can't find the article online but looks like yes the concourse is covered by the new office development, with what looks like a light well between the office and the existing hotel. Then the rest of the light seems to come from the platform area and the entrances, given very high ceilings and more open space.
I'm always overly optimistic about these things, but I think the high ceilings will make a big difference. It's far cry from cannon street or charing X where the oversite development feels like the ceiling is right on top of you.