SISA uses a one day interview process. Candidates give a 30 minute talk and then talk one-on-one with around 6 current employees. Lunch is typically a more casual discussion with one or two team members. In my case I know several of the team members beforehand, and had an informal lunch meeting with one of them before formally applying. After deciding to proceed with the formal interview the process was fairly streamlined: I had a one day interview (talk plus one-on-ones) and received an offer shortly afterward. The formal interview process at the time seemed a little ad hoc; the recruiter forgot to mention that I would need to give a presentation, so I was somewhat surprised when expected to give a talk first thing in the morning. Luckily I regularly give talks about my work and so had plenty of talk materials to choose from. Now that I can see behind the curtain, a big issue with the interview process is that the recruiters are overloaded; SISA as a whole is growing so fast that they have a _lot_ of candidates to juggle. As a result, do yourself a favor and contact the employee (not recruiter) who contacted you and work with them to find out exactly what to expect the day of the interview. They have more time to help you figure out exactly what to expect.

A couple of phone screens, then a group Portfolio review with 10-20 people and some discussion, then individual sessions with 1-3 people, mostly clarifying your experience and fit to job & team.