Pretty good, C++ and other system questions, such as computer network, operating system, etc. I think it's not that difficult. If you have already taken courses about them, it would be okay

Applied online for a different position. Received a phone call from an internal recruiter in ~10 days. The recruiter said my background matches a Quant Dev position better, but also explained that the position is not available yet. While waiting for the position to be approved, I completed the online coding test, but received no further updates. About 3 weeks later I noticed that a Quant Dev position was open, but disappeared within a few hours. I reached out to the recruiter, but quickly received a message of rejection. The email listed reasons why I was rejected, but the reasons were so vague that they are clearly an afterthought. I understand that Optiver has a feedback-driven culture. But the interview experience seems to suggest that 1.) feedback is one-directional rather than a process of discussion; and 2.) saying something quickly is prioritised far above thinking carefully before saying it.