2 phone rounds + onsite (5 interviews of about 1 hour each); fit was only measured implicitly, most of the time was spent doing math questions. Two of the five onsite interviews were collaborative with the other person applying for the internship that day. Problems generally speaking had some sort of tricky edge/corner case to take into account; interviewers look for your ability to identify such cases and to be critical of your own first intuitions. Although there was no explicit fit portion of my interview, personality seems to be evaluated at least implicitly. Also key is keeping cool / staying calm yet not overconfident.

I had a phone screening call from a recruiter, they asked some standard probability questions, bayes rule, and expected value about dices. Overall experience was pretty good. Make sure you prepare your probability