First assessment, then case call, then final round in person. Assessment tests how good are you at logic and calculation but more interesting than plain mental math, involves non-standard thinking. Future rounds are person-driven, also oriented at how you think
I applied online. I interviewed at Jane Street (London, England)
Interview
The interview process consisted of a difficult (as a first year computer science student) coding exercise. I would recommend preparing before undertaking it (something I did not do). I probably have not reached the next stage so that is all I have to say.