From what I recall it was pretty seemless, and I was asked challenging and interesting problems as part of the process. It was obvious they became particularly interested in me as a candidate after one of the initial interviews. From there it was pretty frictionless.

Initially was a video call with the recruiter which was very friendly. He went through some details of the resume, interests of the company, salary expectations, relocation preferences. The second is a technical interview with very broad topics ranging from internet protocols to databases, API alternatives and modern C++ knowledge (code review). The interview in my concept was difficult but it also made it clear the depth of expertise they were looking for. The interviewer was very respectful but also trying to test the limits of your knowledge in all the different topics The second interview was a live coding session with two problems. The first one being how to check if a given string was or not a palindrome, to propose a solution, propose improvements of your solution and think of edge cases. The second problem included a long statement to solve the traversal of a tree using BFS. The third interview is a meeting with team members and CTO but I didn't go through it. The engineers that interviewed me were all very knowledgeable, with more than four years in the company, one of them seemed disengaged and not really focusing on the interview but doing some other work in parallel but might have just been perception.