Phone call with one of the company heads, who then contacted my references and called me for an onsite day. There was a hour-long research talk, many 1-on-1 and 2-on-1 sessions with 12-14 people total, and a dinner at the end. Several questions on my talk, and many standard quant brainteasers that were fairly easy, but I was not well prepared at the time and did poorly. Most people were quite friendly, but some odd personalities as well. Some 2-on-1 sessions had the interviewers arguing with each other, and the CEO just left me alone in his office to work out a problem without talking much. They mostly hire experienced people from academia and industrial research labs, not new PhDs. Still good experience.