Extremely casual. I received a tour of the facility and had a sit-down interview with two engineers. The in-person interview process was long (about an hour and a half) even though I was promised that it would take at most 1 hour. At about midnight, I received a generic rejection email with no further clarification. The interviewer didn’t ask too many technical questions he preferred to talk about the products the company makes, his personal passions, etc. I would say avoid interviewing in-person (and at this company overall) and try asking for a remote option unless you have a referral.