I had a phone interview, then an onsite interview(4 rounds) about 10 days later at their head quarter. I would say really HORRIBLE interview experience. The second round I was sharing video screen with an interviewer, but it turned out that guy in the screen is also a Citadel candidate in London who is also interviewing with Citadel. It's really embarrassing when we found out the truth that none of us are Citadel employee. The third round the interviewer was trying to share a online coder pad with me(He is also remote), and found out HR didn't provide me a laptop, we wait 10 minutes and then we found out the laptop was locked and neither of us have password. The last round my initial interviewer couldn't make it (probably have some meeting or w.e.), and HR told me she would find someone else to interview me, and I wait almost an hour so they find me an temporary interviewer. I would say they are pretty bad at managing their candidates' interview. I didn't think they are really try to interview me, but more likely to grab someone random for training their own employees interviewing skill. I feel really sorry for Citadel, and hope that hiring manager should be fired.

10 min introduction involving resume run-through, followed up by some short basic technical questions, then 45 min coding problem (2 related parts, easy/medium difficulty, BFS algorithm) interviewer was kind and helped