The first stage is a technical written test. The example of the test (found on their website) is slightly more difficult than the actual test (my opinion). The written test went well for me. Topics were very similar to that of the test on their website, from basic probability, distributions, option pricing, regressions, etc.
The second round was a video interview, also exclusively technical questions. The interviewer was not helpful and wasn't friendly. The questions were interesting, but the experience overall wasn't great.