Datadog has a very in depth interview process covering basically everything you would expect (coding, design, delivery management, people management, etc). They provide plenty of documents for preparation and a rough outline of what each interview entails to really give you the best chance of success and it's up to you to make the most of that. I wouldn't say any particular interview is difficult, but it's a lot of interviews covering a lot of topics. At the conclusion of the process, they provide not just a boilerplate "we had many qualified candidates but unfortunately..." email, but the recruiter will actually hop on a call with you and go through high-level feedback from each individual interview, which set me up very well for future interviews with other companies. In my case, I didn't make the cut because I didn't go into enough low-level details in the technical interviews. They would rather hire people who have 10/10 knowledge in some areas and 5/10 in other areas than people with 7-8/10 knowledge across the board, so go into their interviews knowing that it's okay to hand wave some details of your designs as long as you can be very detailed in other areas.

I had a call with a Director of Eng. He seemed to be focused on something else and was seemed disinterested in being there. The feedback he gave was that I was too junior for an M1 role.