Common system based on multiple interviews in one day, CI calls it a track. This is ¨somewhat¨ required but some key hires and consultants are hired without this process.
There is little to zero training on how to interview at CI so the experience is predicated upon who is on your track and the personalities are very very diverse. There is a high probability of out of bounds or personal question. Finally, a big part of the process is candidate interviewing CI. Most employees know that it is a difficult and peculiar place and want to prepare the candidate as much as possible to avoid <90 quit.