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Design a Real-time Chat System is a hard system design interview question covering websockets, message delivery, presence, fan-out — the kind asked at FAANG (Facebook/Meta, Apple, Amazon, Netflix, Google) and AI-first companies like Anthropic, OpenAI, and Nvidia.
Design a real-time messaging system. Users should be able to send messages to individuals and groups, see online presence, and receive messages instantly.
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A full interview loop is more than one round. These are the others, each with what is on the site for it.