They want to see how well you think. They're looking for smart people who can thrive in their culture, not for particular finance or management skills. They want you to argue clearly, show an ability to change your mind, and be absolutely sincere. The other reviewers say it all. This isn't like a typical interview. You'll be asked to take and defend positions on political and philosophical topics. It's a good experience, and well worth your time even if you're skeptical of the place. They're aware that people might just want to make a ton of money and work somewhere prestigious, and they aren't looking for people like that.

There were multiple rounds of interview. Largely a test on culture fit, and overall it is what is to be expected if you prepare and do your research. I enjoyed the process.