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Openai·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say
May 2026

Summary

ML coding round at OpenAI for a SWE role, focused entirely on cleaning human annotation data. The problem was open-ended in a way I wasn't fully prepared for, more of a system design meets ML pipeline question than a typical coding problem.

Questions Asked (1)

Q1

Design and implement a method to detect and filter bad annotations from human-labeled data. Given labeled samples with optional annotator IDs, confidence scores, timestamps, and a small gold set, determine which annotations to drop and which annotators to downweight.

Algorithms & Data StructuresTechnical Trade-offsSystem Design
Author's notes

This one sprawled in a way I didn't expect.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and data characteristics, then propose a hybrid approach combining rule-based heuristics (e.g., confidence thresholds, time anomalies) with statistical methods (e.g., agreement with gold set, annotator reliability scores). Emphasize iterative refinement, validation against the gold set, and trade-offs between precision and recall in filtering.

Pro tip: Demonstrate awareness of the cold-start problem for new annotators and propose a Bayesian or smoothing approach to avoid over-penalizing them. Also, mention the importance of monitoring filtered data's impact on downstream model performance.

1. Clarify Requirements and Data

Ask about the size of the gold set, whether annotator IDs are consistent, and the cost of false positives vs. false negatives in filtering. Understand the downstream task and how filtered data will be used.

2. Define Quality Metrics

Establish metrics such as annotator accuracy on gold set, inter-annotator agreement, confidence calibration, and anomaly detection in timestamps. Use these to score annotations and annotators.

3. Design Filtering and Weighting Algorithm

Combine heuristics (e.g., drop low-confidence, outlier timestamps) with a probabilistic model (e.g., Dawid-Skene) to estimate true labels and annotator reliability. Output per-annotation drop decisions and per-annotator weights.

4. Validate and Iterate

Evaluate the filtering on the gold set and via cross-validation. Monitor precision/recall of bad annotation detection and adjust thresholds. Consider A/B testing impact on model training.

5. Implement and Monitor

Build a scalable pipeline that can handle large datasets, with logging and dashboards for annotator performance. Allow for periodic re-evaluation and updating of weights as more data arrives.

Key Points to Mention

  • Use of gold set for supervised calibration of annotator reliability
  • Probabilistic models like Dawid-Skene for estimating true labels and annotator confusion matrices
  • Handling missing or optional metadata (e.g., annotator IDs, confidence scores) gracefully
  • Trade-offs between aggressive filtering (losing data) and conservative filtering (keeping noise)
  • Cold-start problem for new annotators and smoothing techniques
  • Scalability and efficiency considerations for large-scale annotation pipelines

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