Your question is Rate Limiting at Scale. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
How would you design a rate-limiting system for an API gateway that handles billions of requests per day?
Explain the algorithm, policy model, distributed architecture, storage strategy, failure behavior, observability, and rollout plan. Make your assumptions explicit and discuss trade-offs involving accuracy, latency, availability, fairness, and cost.
