I applied online. The process took 1+ week. I interviewed at Optiver (Amsterdam) in Aug 2022
Interview
Really nice initial test and question. But, they don't have firm reasons to reject during the HR round. Please test some technical skills first. Anyways I am making more money now
Online assessment including Hackerrank. After 2 months I received an invitation for a HR round (the classic stuff), then a technical round, take home assignment then final round split into technical then HR.
Online assessment with 30 timed multiple-choice questions. You have a minute and half for each question, Once the timer runs out you can't go back to that question. A big portion of the problems involve random walk. Some questions require an exact solution, and some are estimates.
A long and exhausting OT of a few sections. Then some interviews on standard green book questions. In between one HR interview. Final round on a take-home ML project. Overall nice experience and HR provides feedback throughout all interviews.