I never spoke to an actual person. They have you do a codesignal assessment first. The assessment is not overly difficult, but they do not give you enough time. Using a verbose language will make it harder on you. I got my score back as "expert" in most categories and received a rejection email a day later.

The whole process is smooth, and very enjoyable. First round is codeSignal test, 70 - 120 mins to complete, questions are not hard but does require time to complete. 2 written questions regarding API and Database, and 2 practical coding tasks. No leetcode. After that, a recruiter would be in touch if you passed that, and talk abt the company and interview process. Then it is 6 rounds of panel interview, everyone is super nice and knowledgable, and seems enjoying their job at Circle. Out of 6 rounds, only 1 is coding, again on codeSignal, but it is very practical, not leetcode style. 3 rounds are system design, very standard. One of them will be a system you designed in the past. 2 rounds of behaviour, one with hiring manager and one with a VP, all very standard, like Amazon LP style.