Welcome to your interview.
The question is on your right: High-Concurrency API Design. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
How do you approach designing an API that needs to support thousands of concurrent users while maintaining low latency at Inc.?