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

Senior
Jul 2026

Summary

System design round at OpenAI for an ML Engineer role, centered entirely on one meaty question about building a content moderation pipeline for harmful videos. No behavioral fluff, just a deep technical dive that covered a lot of ground fast.

Questions Asked (1)

Q1

Design a complete system to detect and moderate harmful videos on a large platform, covering multiple violation categories, both upload-time and retroactive scanning, a mix of automated and human review, low false positives and false negatives, and support for appeals and audit trails.

System DesignTechnical Trade-offsProduct Analytics & Metrics
Author's notes

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and scale, then propose a multi-stage pipeline that combines fast automated classifiers for upload-time filtering with periodic batch scanning for retroactive detection. Emphasize human-in-the-loop review for ambiguous cases, and design feedback loops to continuously improve model accuracy while minimizing false positives/negatives. Finally, outline the appeals and audit trail systems to ensure transparency and accountability.

Pro tip: Quantify trade-offs: e.g., discuss how adjusting classification thresholds affects precision/recall and the resulting human review load, showing you understand the operational costs and can make data-driven decisions.

1. Clarify Requirements and Scale

Ask about platform scale (uploads per second, total videos), violation categories, latency requirements, and accuracy targets. This sets the stage for designing a system that balances performance and cost.

2. Design Multi-Stage Detection Pipeline

Propose a pipeline: fast hash-matching for known violations, lightweight ML models for immediate triage, and heavier models for deeper analysis. Include both upload-time (synchronous) and retroactive (asynchronous batch) scanning.

3. Integrate Human Review and Feedback Loops

Route low-confidence predictions to human moderators, and use their decisions to retrain models. Implement active learning to prioritize uncertain cases for labeling, improving efficiency.

4. Optimize for Low False Positives/Negatives

Discuss threshold tuning, ensemble methods, and category-specific models. Consider business impact: false positives harm creators, false negatives harm users. Use metrics like precision/recall and cost-sensitive learning.

5. Implement Appeals and Audit Trails

Design a transparent appeals process where creators can contest decisions, with human re-review. Maintain immutable logs of all actions (automated and human) for auditing and compliance.

Key Points to Mention

  • Scalability: distributed processing, sharding, and caching for high-throughput inference.
  • Model selection: trade-offs between speed and accuracy (e.g., MobileNet vs. ResNet, or two-stage cascades).
  • Human-in-the-loop: review queue prioritization, moderator training, and quality control.
  • Metrics: precision, recall, F1, AUC-ROC, and business metrics like appeal rate and time-to-action.
  • Feedback loops: continuous retraining, active learning, and handling concept drift.
  • Audit and compliance: logging, versioning of models and decisions, and explainability for appeals.

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