I applied to their London office from another city. First I had 3 phone interviews 1 hour each. Further they gave a programing exercise on asset return forecasting, I spent 2 days on doing it. Then I went to London 2 times for a full day of interviews. So there were 15 interviews and 1 programming exercise in total. The first phone interview was very technical and mostly consisted of small maths problems on calculus, linear algebra, probability theory and statistics, and also some basic questions on finance. All the other interviews followed a similar : first they asked me to tell about my previous exprerience, about my phd research, and then asked maths problems on linear algebra, probability, machine learning, optimization. There were also questions about Python and algorithms. Some finance related questions, e.g. on factor models, trading strategies backtesting, common facts about market microstructure (volume, spread, volatility behaviour during a trading day). All interviewers were very competent and friendly. The best interview experience that I've had so far.

One on One interview with a research team manager. He probes probability questions. Mostly conditional. Atmosphere quite relaxed. It was great fun. Id do it again. Every time it was cool.