Optiver

HR -> OA -> phone -> two round final OA was a bit tedious. Phone was standard coding. Final was difficult: one system design with no coding and one technical.

A challenging C++ problem to solve. It was not something an ordinary developer could solve, and it was one I wish I had studied more for. Afterwards, I did not get an interview and received no feedback.

Finished the interview in about a week. Recruiters didn't rush me, gave me time for competing offers, and kept in touch regularly during the process to address concerns. Great experience.