The process consisted of two steps. First, a technical phone screen with a code writing component. if you passed that, then they bring you on-site for a day-long series of interviews.
For the on-site interviews, I had 5 interviews: 2 coding interviews, 2 design theory interviews, and a "social" interview. My understanding is that how many interviews and what kinds of interviews you have depends on the role you're interviewing for.
Overall, the process felt tough but reasonable, given how competitive those positions are. They provide a lot of material in advance to allow you to prepare well; others would be advised to take advantage of that material.