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Anthropic·Software Engineer·Technical Phone Screen·Senior

Senior
Jun 2026

Summary

Coding round at Anthropic for a software engineer role, focused entirely on building an LLM-based agent from scratch. You actually write the code, not just talk through it, which I did not fully expect going in.

Questions Asked (3)

Q1

Build a working agent loop that uses an LLM API to solve a given task, including tool definitions, output parsing, and termination logic.

System DesignAPI & IntegrationsTechnical Trade-offs
Author's notes

This is the whole interview, basically.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the task and constraints, then outline a modular agent loop: define tools, call the LLM, parse its output, execute tools, and repeat until a termination condition. Emphasize robustness, error handling, and observability throughout.

Pro tip: Mention that you'd log every LLM request/response and tool call for debugging and evaluation, and that you'd set a max iteration limit to prevent infinite loops.

1. Clarify requirements and constraints

Ask about the task type, available tools, LLM API specifics, and any latency/cost constraints. Confirm the expected termination conditions.

2. Define tool interfaces

Specify each tool's name, description, and parameter schema in a format the LLM can understand (e.g., JSON schema). Ensure tools are idempotent and return structured results.

3. Design the agent loop

Outline the loop: send conversation history and tool definitions to the LLM, parse the response for tool calls or final answer, execute tools, append results, and repeat.

4. Implement output parsing and error handling

Use a robust parser (e.g., regex or JSON) to extract tool calls and arguments. Handle malformed outputs, API errors, and tool failures with retries or fallbacks.

5. Define termination and safety logic

Set conditions for termination: explicit final answer, max iterations, timeout, or error threshold. Include logging and monitoring for each step.

Key Points to Mention

  • Tool definition format (e.g., JSON schema) and how the LLM selects tools
  • Parsing LLM output for tool calls vs. final answer, including handling of multiple tool calls
  • Error handling: API failures, invalid tool arguments, and tool execution errors
  • Termination conditions: max iterations, timeout, and explicit stop signals
  • Observability: logging, tracing, and metrics for debugging and evaluation
  • Cost and latency considerations: batching, caching, and model selection

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

Q2

What prompting techniques did you use in your agent design, and what are the trade-offs between them?

Technical Trade-offsAdaptability & Ambiguity
Author's notes

They asked me to justify my choices after I coded it up.

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AI HintsAI Generated

Suggested Approach

Start by briefly describing a specific agent you designed and the prompting techniques you used, then dive into the trade-offs between them. Focus on how you evaluated and chose techniques based on task requirements, and conclude with lessons learned or how you'd approach it differently next time.

Pro tip: Show that you understand prompting is not one-size-fits-all: mention that you A/B tested techniques and measured performance against clear metrics, which demonstrates a rigorous, empirical approach valued at Anthropic.

1. Set the context

Briefly describe the agent's purpose, the task, and the constraints (e.g., latency, cost, accuracy) to ground your choices.

2. List techniques used

Name 2-3 specific prompting techniques (e.g., few-shot, chain-of-thought, ReAct) and explain why you chose each for that agent.

3. Analyze trade-offs

For each technique, discuss pros and cons in terms of performance, cost, latency, reliability, and complexity.

4. Share evaluation and iteration

Explain how you measured effectiveness (e.g., success rate, token usage) and iterated to find the best balance.

5. Conclude with learnings

Summarize key takeaways and how you'd apply them to future agent designs, showing adaptability.

Key Points to Mention

  • Few-shot prompting: improves accuracy but increases token cost and latency.
  • Chain-of-thought: enhances reasoning for complex tasks but can be verbose and slow.
  • ReAct (Reason + Act): enables tool use and dynamic decision-making but adds orchestration complexity.
  • Self-consistency: boosts reliability by sampling multiple outputs but multiplies cost.
  • Trade-offs between performance, cost, latency, and maintainability.
  • Empirical evaluation: A/B testing, metrics like task success rate, and iterative refinement.

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

Q3

How would you evaluate whether your agent is correct and robust enough for production use?

A/B Testing & ExperimentationRoot Cause Analysis
Author's notes

Caught me a little flat-footed.

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AI HintsAI Generated

Suggested Approach

Start by defining what 'correct' and 'robust' mean for your specific agent, then outline a multi-layered evaluation strategy that combines offline testing, online experimentation, and continuous monitoring. Emphasize the importance of realistic failure scenarios and iterative improvement based on data.

Pro tip: Frame your answer around the principle of 'test like you fly'—simulate production conditions as closely as possible, including edge cases and adversarial inputs, and always have a rollback plan. Show that you think about evaluation as an ongoing process, not a one-time gate.

1. Define Success Criteria and Failure Modes

Clearly specify what correct and robust mean for your agent in terms of functional accuracy, safety, latency, and reliability. Enumerate potential failure modes, including edge cases, adversarial attacks, and distribution shifts.

2. Offline Evaluation with Comprehensive Test Suites

Develop a diverse set of test cases covering normal, edge, and adversarial scenarios. Use metrics like precision, recall, F1, and robustness scores, and perform error analysis to identify weaknesses.

3. Online Experimentation and A/B Testing

Deploy the agent in a controlled production environment using A/B tests or canary releases. Compare against baselines or previous versions, measuring both business and system-level metrics.

4. Continuous Monitoring and Root Cause Analysis

Implement real-time monitoring for performance drift, anomalies, and failures. When issues arise, conduct root cause analysis to understand and fix underlying problems.

5. Iterate and Improve

Use insights from evaluations to refine the agent, update test suites, and enhance robustness. Establish a feedback loop for ongoing improvement.

Key Points to Mention

  • Define clear, measurable success criteria and failure modes specific to the agent's purpose.
  • Combine offline testing (unit, integration, adversarial) with online A/B testing for comprehensive coverage.
  • Use canary releases and feature flags to safely roll out changes and enable quick rollbacks.
  • Monitor production metrics (e.g., latency, error rates, user feedback) and set up alerts for anomalies.
  • Conduct root cause analysis on failures to drive iterative improvements.
  • Consider ethical and safety implications, especially for AI agents, and include red-teaming or adversarial testing.

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