Went through the Vercel senior SWE loop earlier this year, specifically for a role on the infrastructure team. Going to write up the system design round because it was pretty different from what I expected coming from bigger companies.
First: Vercel doesn't call levels "L5" publicly but internally the senior IC role maps roughly to what FAANG would call L5/E5. Worth knowing for calibration.
The prompt. Mine was around CDN edge caching and invalidation at scale. Very on-brand for what they actually build. The interviewer wanted me to design a system that could push cache invalidations to tens of thousands of edge nodes within a few seconds of a deploy. So they're literally asking you to design the thing their product does.
I thought this was actually nice compared to the usual "design Twitter" prompts. The problem space was narrower and more concrete. But it also meant you need to know their product well going in. If you don't understand how Vercel's edge network works at a high level, you'll flounder.
What they cared about. The interviewer pushed hard on failure modes and consistency tradeoffs. What happens if an invalidation message gets lost? Do you guarantee exactly-once delivery or accept at-least-once? How do you handle a node that was offline during the invalidation window? Classic distributed systems territory but applied.
They also asked about observability. How do you know when invalidation completes? What metrics do you surface? This felt like they were checking whether I think like someone who'll own the system post-launch.
Format. 60 minutes, on a shared Google Doc (no fancy whiteboard tool). Write-as-you-go, they're reading along. The interviewer asked follow-up questions throughout rather than letting me monologue for 20 minutes first. I liked that rhythm.
Depth. This felt like a genuine staff-level conversation, not a rote checklist. I came from a big-co where system design interviews got formulaic and the Vercel one was refreshing. But also harder to prep for because you can't just memorize the "design a URL shortener" answer and you're done.
Prepare by actually reading their blog posts and the Vercel changelog. They write a lot about how their infrastructure works. That background makes you sound like you've thought about their actual problems.