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Snap·Machine Learning Engineer·Technical Phone Screen·Senior

Senior
Apr 2026

Summary

ML engineer interview at Snap, came down to a technical question about evaluating LLM performance. Pretty short exchange from what I remember, but the question itself required some real depth.

Questions Asked (1)

Q1

What methods or metrics would you use to evaluate how well an LLM is performing?

Product Analytics & MetricsTechnical Trade-offs
Author's notes

This is one of those questions where you can go a lot of directions and that's kind of the problem.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the LLM's specific use case and objectives, then propose a mix of automated metrics, human evaluations, and business KPIs. Emphasize the importance of aligning evaluation with product goals and iterating based on feedback.

Pro tip: Highlight the trade-offs between automated metrics and human judgment, and suggest a tiered evaluation system that scales from offline benchmarks to online A/B tests. This shows you understand both technical rigor and product impact.

1. Define Objectives and Scope

Clarify the LLM's purpose (e.g., content recommendation, chat, summarization) and the key performance indicators that matter for the product. This ensures evaluation is aligned with business goals.

2. Select Automated Metrics

Choose appropriate automated metrics such as perplexity, BLEU, ROUGE, BERTScore, or task-specific accuracy. For generative tasks, consider diversity and coherence metrics.

3. Incorporate Human Evaluation

Design human evaluation protocols (e.g., Likert scales, pairwise comparisons) to assess qualities like relevance, fluency, and safety. Use crowdworkers or domain experts as needed.

4. Monitor Business and Online Metrics

Track product-level metrics (e.g., user engagement, retention, click-through rate) through A/B tests or online experiments to measure real-world impact.

5. Iterate and Refine

Continuously analyze results, identify gaps, and refine both the model and evaluation strategy. Use feedback loops to improve performance over time.

Key Points to Mention

  • Task-specific metrics vs. general language metrics
  • Human evaluation for subjective qualities (e.g., helpfulness, safety)
  • Business KPIs (e.g., user engagement, retention) and A/B testing
  • Trade-offs between automated metrics and human judgment
  • Benchmark datasets and leaderboards for comparison
  • Ethical considerations and bias evaluation

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