I went all the way to the "last interview". The whole process was unsatisfyingly slow. First off, I waited a whole week to get a response for the first phase, and that's because I sent an email asking for a sign of life; even after this silent week had passed, it took a whole day for me to get a response at all. When I got through the second phase, I had to wait almost a week to have the interview for the third phase, then another two days to get to the final round of interviews. Finally, I had to wait one more week for the final response. Overall, a whole month went by of those 1-hour-ish interactions per week, which is unsatisfying.
In the end, my application was turned down because "background and personality were not a good fit". That felt out-of-place, since those aspects should arguably be screened out in the first few steps of considering a candidate at all. Considering I had spent this whole time going through all of the phases, I sent one last email politely asking about what was lacking in my candidacy, for which I got no response so far; considering the pace of things, I'm feeling negative about my chances.
Looking back, going through the motions was a very unsatisfying experience. I wish the company would be more thorough and eager in running its hiring process; that would help to avoid wasting the candidate's time and energy.