The interview process was pretty long: 4 interviews + a homework. First, a classic interview with the recruiter. Then an development exercise to do at home on your free time. They say you don't have to spend a tremendous amount of time on it, but it seems the expectations are pretty high so maybe you should. Then 2 technical interviews (about 1 hour each) with 2 Proton's engineers: the first was a pair programing, the second was a system design interview. Both interviews were pleasant, no tricky questions. Finally a more casual interview (about 45min) with a manager.

The interview process consisted of an initial screening, an interview with the Engineering Manager, a pairing session/take-home assignment, a system design interview, and a final interview. I completed all stages of the process but did not receive an offer, as they decided to move forward with another candidate.