@tharg saidCastling isn't supported currently - only the Chess960 starting positions.
Is it me or does RHP not apply the rules correctly?
For example I have a game as Black and have Kg8 and Rh8 and I am not in check and the pieces have not been moved. I should be able to move Rh8-f8 but can’t. Maybe it’s in beta?
Therefore, 960 games are just treated as thematic/unrated games.
But, the work to support 960 is complete (including the castling rules), it is just a matter of merging support into RHP daily/correspondence. You can see this now in the live chess play where it is available already.