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Anthropic·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
May 2026

Summary

Did a system design round at Anthropic for a software engineer role. Classic prompt, but I fumbled the time management pretty badly and never got to the parts that probably matter most.

Questions Asked (1)

Q1

Design a one-on-one chat system.

System DesignAPI & IntegrationsTechnical Trade-offs
Author's notes

Sank too much time into requirements and API surface area.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements (scale, features, latency, consistency) and then propose a high-level architecture with key components like WebSocket servers, message queues, and storage. Dive into critical design decisions such as message delivery guarantees, ordering, and scaling, while discussing trade-offs and potential bottlenecks.

Pro tip: Emphasize the importance of message ordering and delivery guarantees per conversation, and discuss how to handle offline users and multi-device synchronization. Show awareness of operational concerns like monitoring and rate limiting.

1. Clarify Requirements

Ask questions to understand scale (DAU, messages per second), features (group chat, read receipts, media), latency, consistency, and availability needs.

2. High-Level Architecture

Outline core components: clients, WebSocket servers for real-time communication, message queue (e.g., Kafka) for decoupling, storage (e.g., Cassandra for messages, Redis for presence), and a service for push notifications.

3. Deep Dive into Key Components

Discuss message flow: client sends via WebSocket to server, server publishes to queue, consumers persist and deliver to recipients. Cover message ordering (per conversation), delivery guarantees (at-least-once, deduplication), and offline handling (store and forward, push notifications).

4. Scaling and Reliability

Explain how to scale WebSocket servers (load balancing, sticky sessions), partition message queues, and replicate storage. Discuss handling failures (retries, idempotency) and ensuring high availability.

5. Trade-offs and Optimizations

Compare design choices (e.g., WebSocket vs. long polling, SQL vs. NoSQL, consistency vs. latency) and suggest optimizations like caching, batching, and compression.

Key Points to Mention

  • WebSocket for real-time bidirectional communication, with fallback to long polling
  • Message queue (e.g., Kafka) for decoupling and handling spikes
  • Storage: Cassandra for messages (write-heavy, time-series), Redis for presence and session data
  • Message ordering per conversation using sequence numbers or timestamps
  • Delivery guarantees: at-least-once with deduplication, or exactly-once if feasible
  • Offline message handling: store messages and send push notifications when user comes online

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.