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Openai·Machine Learning Engineer·Onsite - System Design / Architecture·Senior

Senior
Apr 2026

Summary

System design round at OpenAI for an ML Engineer role, centered entirely on one big open-ended problem about handling uncertainty in a ChatGPT-style assistant. No small warmup questions, just straight into the deep end for the full session.

Questions Asked (1)

Q1

Design a system for a ChatGPT-like assistant that gracefully handles situations where the model doesn't know the answer or can't answer reliably. Cover the architecture, how the system decides what to do (answer, clarify, retrieve, or refuse), and how you'd measure whether it's working.

System DesignTechnical Trade-offsProduct Analytics & Metrics
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AI HintsAI Generated

Suggested Approach

Start by framing the problem as a reliability and trust challenge, then propose a modular architecture with a decision layer that routes queries based on confidence, knowledge boundaries, and risk. Walk through the decision logic (answer, clarify, retrieve, refuse) and finish with concrete metrics for offline and online evaluation, emphasizing trade-offs between helpfulness and safety.

Pro tip: Show that you understand OpenAI's iterative deployment philosophy: design for graceful degradation and continuous learning from user feedback, rather than trying to solve uncertainty perfectly upfront.

1. Clarify Requirements and Constraints

Define what 'doesn't know' means (e.g., out-of-distribution, ambiguous, or high-risk queries) and the system's goals: maximize helpfulness while minimizing hallucinations and harmful outputs. Consider latency, cost, and user experience constraints.

2. Propose a Modular Architecture

Outline components: a query understanding module, a knowledge/confidence estimator, a retrieval system, a decision router, and a response generator. Emphasize separation of concerns and fallback mechanisms.

3. Define Decision Logic and Policies

Explain how the system decides among answer, clarify, retrieve, or refuse. Use signals like model confidence scores, uncertainty quantification, retrieval relevance, and safety classifiers. Describe thresholds and how they are tuned.

4. Detail Handling for Each Action

For each action, describe the implementation: e.g., for clarify, generate targeted questions; for retrieve, use RAG with source attribution; for refuse, provide safe fallback and suggest alternatives. Include how to handle partial knowledge.

5. Define Evaluation Metrics and Iteration

Propose offline metrics (e.g., hallucination rate, refusal accuracy, retrieval precision) and online metrics (e.g., user satisfaction, task success, engagement). Describe A/B testing and feedback loops for continuous improvement.

Key Points to Mention

  • Uncertainty quantification techniques (e.g., model confidence, entropy, ensemble disagreement) and their limitations.
  • Retrieval-augmented generation (RAG) with citation and source reliability checks.
  • Safety and policy layers to detect harmful or sensitive queries and trigger refusals.
  • User experience design for clarifications and refusals (e.g., tone, helpful suggestions).
  • Trade-offs between answering, clarifying, retrieving, and refusing (e.g., over-refusal vs. hallucination).
  • Evaluation frameworks: offline benchmarks, human evaluation, and online A/B testing with guardrail metrics.

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