Just cleared the Datadog onsite. Sharing the breakdown because 'final round' is doing a lot of work for what is actually a pretty substantial loop.
Total rounds in the final stage: 5 back to back, all virtual, one day. They do offer to split it across two days if you ask early enough.
Here's what each round looked like for me (SRE / infra track):
Round 1: Coding 1. Algorithm/DS. CoderPad, live. Medium difficulty. I got a string parsing problem related to log formats which was very on-brand.
Round 2: Coding 2. More design-oriented. I got the sliding window rate limiter implementation. 45 min.
Round 3: System design. The big one. Mine was around distributed tracing ingestion. 60 min. See other threads on this.
Round 4: Behavioral / culture. One interviewer. Heavy on cross-team collaboration and handling ambiguity. They also asked about a technical failure and what I'd do differently.
Round 5: Hiring manager. Part behavioral, part role fit, part 'what are your career goals.' This one varies most by team.
Debrief timeline: they told me 5-7 business days. I heard back in 4. They do actually give feedback if you don't get an offer, which is more than most companies do.
Energy level during the day: it's exhausting. I had a 20 min break between rounds 3 and 4. Eat before you start, have water, close your other tabs. The last round is when fatigue hits and they can tell.
Overall: they're not trying to trick you. The problems are hard but relevant to what they actually build. If you've used Datadog's product, it helps to understand the scale they operate at.