Two phone interviews (1 hour each), then onsite interview (5 - 6 hours) with a presentation on a "6 - 10 hour" project + a previous project you worked on. Several 1-on-1 interviews. Project + presentation easily took 30 hours. A lot of work and time for no guarantees. Everyone was friendly.

I got two rounds, HR and Engineering. The interviewer was polite and casual. The questions weren't hard, but they required knowing specific equations off the top of your head for hand calculations without document reviews. They expected a specific number as an answer, which felt absurd; testing for IQ, situational handling, or work ethic would make more sense.