Online assessment (GMAT-style maths questions), then 3 rounds (I got through to the final round).
First round was an in-office assessment (same types of questions as the online assessment) and a case interview. Second round is two back to back case interviews. Third round is three back to back case interviews. With each round, the interviewers became increasingly senior. Interviews are all 45 minutes long, which breaks down into roughly 15 minutes on personal fit, 20/25ish minutes on a case, and the last few minutes to ask questions. After the final round interviews you get an office tour.
Interviewers very nice, and seemed to be genuinely engaged as I was telling them stories for the fit portion of the interview, as were the HR staff who took care of you before/after. Cases themselves were genuinely quite interesting, and your interviewers will have worked on that case, so you can ask questions about it at the end. They also give you a little card for each interviewer with their work history, what sort of projects/industries they work on, which I thought was a really nice touch. Food and drink was provided, which was great (especially at the later rounds with multiple interviews).
Two negatives:
1. Getting feedback - if you get through a round, you're told that the interviewers will call you. While this is obviously great, these interviewers have busy lives. The email states that if you haven't heard back by 24 hours before your interview to contact them and they will sort it out. This happened for me in both cases, and the hassle to chase them is annoying + only being told the feedback at 8pm the night before the final round interviews at 8am makes it hard to improve based on said feedback .... I spoke to some other applicants, and this seemed to be a common issue. For HR: If you're reading, I would recommend giving people the email addresses of the interviewers so they can schedule a time.
2. the way you hear back - so I was told we would hear back 'Friday evening'. Turns out that could mean Friday evening 11:30pm, which was a nice surprise on Saturday morning, but I do think this could be done better. Furthermore, the final decision is communicated via email - I think this would be better done via a phone call, especially if you do get an offer (as other firms do).