Here are the replays https://lichess.org/broadcast/fide-freestyle-chess-world-cha...
I somewhat remeber reading that this format is about playing against book opening, and I thought there is no castling.
Magnus does a castling from king d1 rook h1 which I didn't even know its an allowed move! https://lichess.org/broadcast/fide-freestyle-chess-world-cha...
source : https://en.wikipedia.org/wiki/Chess960#Castling_rules