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Meta·Software Engineer·Onsite - System Design / Architecture·Staff

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Jun 2026

Summary

Meta system design round focused entirely on building an LLM-based agent system from scratch. It was a deep, sprawling question that touched everything from architecture to safety to cost, and I felt like I was constantly playing catch-up on the non-functional stuff.

Questions Asked (3)

Q1

Design an LLM-based agent system end to end, covering functional requirements like task decomposition, tool calling, memory, multi-step reasoning, and multi-agent coordination, plus non-functional concerns like latency, cost, reliability, and observability.

System DesignTechnical Trade-offsAPI & Integrations
Author's notes

This is a monster of a question.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and scale, then propose a high-level architecture that separates concerns: orchestration, tool integration, memory, and multi-agent coordination. Walk through each component, discussing trade-offs between latency, cost, reliability, and observability, and justify design choices with concrete examples.

Pro tip: Emphasize how you would instrument the system for observability and set up feedback loops for continuous improvement, as this demonstrates production maturity beyond just building a prototype.

1. Clarify Requirements and Constraints

Ask questions to understand the use case, expected load, latency requirements, cost budget, and reliability needs. Define functional and non-functional requirements clearly.

2. Design Core Components

Outline the main modules: task decomposition, tool calling, memory management, and multi-step reasoning. Explain how they interact and the data flow.

3. Address Multi-Agent Coordination

Describe how multiple agents communicate, share state, and resolve conflicts. Discuss patterns like centralized orchestration vs. decentralized collaboration.

4. Optimize for Non-Functional Requirements

Discuss strategies to reduce latency (caching, parallel tool calls), control cost (model selection, token limits), ensure reliability (retries, fallbacks), and enable observability (logging, tracing, metrics).

5. Summarize Trade-offs and Evolution

Highlight key trade-offs made and how the design could evolve with scale or changing requirements. Mention potential future improvements.

Key Points to Mention

  • Task decomposition techniques (e.g., chain-of-thought, tree-of-thought) and how to handle failures.
  • Tool calling: API design, error handling, rate limiting, and security considerations.
  • Memory: short-term vs. long-term, vector databases, context window management.
  • Multi-agent coordination: communication protocols, role assignment, conflict resolution.
  • Latency and cost optimization: model distillation, caching, batching, asynchronous execution.
  • Observability: logging, tracing, metrics, and feedback loops for continuous improvement.

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

Q2

How would you handle evaluation and safety for an agent system like this?

System DesignTechnical Trade-offsAdaptability & Ambiguity
Author's notes

Blanked for a second here.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the agent's scope and risk profile, then propose a layered evaluation framework that combines offline benchmarks, online A/B testing, and continuous monitoring. Emphasize safety mechanisms like guardrails, human-in-the-loop, and red-teaming, and discuss trade-offs between safety and performance.

Pro tip: Frame evaluation and safety as a continuous lifecycle, not a one-time gate, and tie it to business metrics like user trust and retention. Show you understand Meta's scale by mentioning automated regression testing and canary deployments.

1. Clarify Agent Scope and Risks

Ask about the agent's capabilities, user interactions, and potential harms (e.g., misinformation, bias, security). This ensures evaluation targets the right risks.

2. Define Evaluation Metrics and Benchmarks

Propose both task-specific metrics (e.g., success rate, latency) and safety metrics (e.g., toxicity, bias). Use offline datasets and simulated environments for initial testing.

3. Implement Online Testing and Monitoring

Describe A/B testing, canary releases, and real-time monitoring for anomalies. Include feedback loops from user reports and automated alerts.

4. Integrate Safety Mechanisms

Outline guardrails like input/output filters, fallback to human agents, and red-teaming exercises. Discuss how to handle edge cases and adversarial attacks.

5. Iterate and Govern

Emphasize continuous improvement through post-mortems, model updates, and cross-functional review boards. Align with Meta's responsible AI principles.

Key Points to Mention

  • Offline evaluation with held-out datasets and adversarial examples
  • Online A/B testing with guardrail metrics (e.g., user reports, safety violations)
  • Human-in-the-loop for high-risk decisions and escalation paths
  • Red-teaming and adversarial testing to uncover vulnerabilities
  • Monitoring and alerting for drift, bias, and performance degradation
  • Trade-offs between safety, latency, and user experience

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

Q3

How would you scale this system to support many concurrent agent runs?

System DesignTechnical Trade-offs
Author's notes

Felt more comfortable here.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the system's current architecture, expected scale, and constraints (e.g., latency, cost, isolation). Then propose a layered scaling strategy: horizontal scaling of stateless components, partitioning of stateful components, and asynchronous processing with backpressure. Finally, discuss trade-offs between consistency, latency, and cost, and how you would validate the design with load testing and monitoring.

Pro tip: Emphasize the importance of defining clear SLOs and using them to drive architectural decisions; this shows you think about scalability in terms of business impact, not just technical metrics.

1. Clarify Requirements and Constraints

Ask about expected concurrency, latency targets, cost budget, and isolation requirements. This ensures your scaling approach is grounded in real needs.

2. Identify Bottlenecks and Stateful Components

Analyze the current system to find components that limit scaling, such as databases, shared caches, or orchestrators. Determine which are stateless vs. stateful.

3. Design Horizontal Scaling for Stateless Components

Propose adding more instances behind a load balancer, using auto-scaling groups, and ensuring idempotency for safe retries.

4. Partition and Replicate Stateful Components

For databases and queues, suggest sharding, read replicas, and partitioning strategies. Discuss consistency trade-offs (e.g., eventual vs. strong).

5. Implement Asynchronous Processing and Backpressure

Use message queues to decouple producers and consumers, and apply backpressure to handle bursts. Discuss rate limiting and circuit breakers.

Key Points to Mention

  • Horizontal scaling with load balancing and auto-scaling
  • Database sharding, replication, and choosing the right consistency model
  • Caching strategies (e.g., Redis) to reduce database load
  • Asynchronous processing with message queues (e.g., Kafka, RabbitMQ) and backpressure
  • Monitoring, metrics, and load testing to validate scalability
  • Trade-offs between latency, cost, and consistency

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