I applied online. The process took 4 weeks.

I would say it is effectively a big waste of time. They are obviously not hiring nor growing, so to get the role you will need some stars to align, and also you will need to completely crush all of the interviews. However, since they don't give feedback, it is hard to know exactly why they reject.

It does not matter if interviewers are neutrally nice to you if there is very little respect for your time. So if you are actually thinking about joining Brex, I would dissuade you a bit—not because I don't think it is impossible or that it is a bad company to work for, but rather because the odds are more prone to be a time sink. If you are interviewing in multiple places, I would put more focus on the other processes.

For instance, the debugging round: it is not hard to find all 4 bugs, but miss one and it is over, and your whole loop can easily be cast aside by trivialities.

In system design, be prepared to be interrupted constantly by questions until you are not able to answer them. You need to know your basics really well, and your answers need to be swift; understanding the logic is not enough, as interviewers want names. This is the hardest interview, as the interviewer is there to antagonize you. They are looking for a reason to discard you, so don't give them any. If you mention something, be absolutely confident you know everything about it.

The AI interview is not transparent; you will never know what you need to do aside from basic requirements. Quite honestly, it is a very silly interview.

Overall, if you have the opportunity and the time, then do try the process. But for most people interviewing, it is going to be a rejection with no feedback and a very long process. Lower your expectations and focus on other processes if possible.

AI round was to vibe code a p2p web app like paypal, what you need to do from here is up to you.