Have interviewed with them in the past. You can expect leetcode questions (easy/med) and data structures. C++ questions (you don't need to be an expert, since they have c++ experts on the software engineering side, but at least know c++11/14 features) and some stats / brainteasers (usual dice throwing games, regression, etc). For the quant research part you would have more stats and maths questions (machine learning and more brainteasers) while for a quant dev position they'll probably indeed ask you about your hpc experience and expect you to know multithreading (again no need to be an expert for quant positions) good luck.