One of the best on-sites I have done in many years as an engineer. I got a good sense of their culture, talked to some really smart people, and had some wildcard questions that challenged and pushed me. Altogether, an excellent interview experience.

It was via Triplebyte, so I jumped straight to the on-site, so I can't say much about the early parts of the process.

Some LeetCode medium and one hard question. I knew theoretically how to solve the hard, but screwed it up and wrote a pseudocode solution as I ran out of time. It was a variant of Dijkstra's Shortest Path problem.

One round of questions was some totally wildcard mathematical or scientific problems to see how I thought.