Did the Twitter (X) senior SWE loop back in February, L5 leveling. Going to share what actually happened in the system design round because the old threads are all pre-acquisition and things have shifted.
The round was 60 minutes with one interviewer. No panel, just one person. They gave me a warm-up question to confirm I could actually draw boxes and arrows, then pivoted to the real thing: design the Twitter timeline. Yes, the actual Twitter timeline. Kind of poetic for a Twitter interview.
What they actually cared about: Fan-out on write vs. fan-out on read was the core tension they wanted to see me navigate. If you don't know what that means going in, you will struggle. They wanted to hear me reason about the trade-offs with celebrity accounts (huge follower counts, can't fan-out 50M writes per tweet) vs. regular users.
I spent probably 15 minutes on that trade-off alone, whiteboarding a hybrid approach. The interviewer pushed back twice, which I think was the point. They weren't looking for the right answer; they wanted to see if I'd crumble or hold my ground and explain my reasoning.
Depth they wanted: Cache invalidation at scale (Redis specifically came up) How you'd handle the firehose of real-time events Rough QPS math. Have actual numbers ready, not just "it's high traffic" What breaks first when the system is stressed
What didn't matter: The specific tech choices were mostly irrelevant as long as I could defend them. Kafka vs. a message queue variant, doesn't matter. The reasoning matters.
Total loop was 5 rounds: 2 coding, 1 system design, 1 behavioral, 1 hiring manager chat. Coding was leetcode medium, one was a graph problem. The system design was the one that actually separated people I think.
One thing that surprised me: no LLD (low level design) round. It was pure distributed system design. So if you're prepping, bias toward scalability problems, not class diagrams.
Comp at offer for SF L5 was around $380K total (base + RSU at target), which felt roughly inline with the post-acquisition bands I'd heard. They did compress the RSU vesting a bit from the old packages.