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Openai·Machine Learning Engineer·Technical Phone Screen·Senior

Senior
Apr 2026

Summary

Went through a technical screen for an ML engineer role at OpenAI. Just the one question but it was deceptively deep once you start pulling on the thread.

Questions Asked (1)

Q1

What happens when you change the context window size of a large language model?

Technical Trade-offsSystem Design
Author's notes

Started with the obvious stuff, longer context means the model can attend to more tokens, more memory, slower inference.

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AI HintsAI Generated

Suggested Approach

Start by defining what the context window is and its role in LLM inference. Then discuss the technical implications of changing its size, covering computational, memory, and quality trade-offs. Finally, relate these to practical considerations like cost, latency, and model performance.

Pro tip: Emphasize that increasing context window size doesn't automatically improve performance; it often requires architectural changes like sparse attention or positional interpolation, and can degrade quality if not trained properly.

1. Define context window

Explain that the context window is the maximum number of tokens the model can attend to when generating text. It determines how much previous information the model can use.

2. Computational and memory implications

Discuss how increasing context window size quadratically increases attention computation and memory usage, impacting latency and cost. Mention techniques like sparse attention to mitigate.

3. Model quality and training

Explain that simply increasing context window without training on longer sequences can lead to degraded performance. Models need to be trained or fine-tuned with longer contexts to effectively use them.

4. Practical trade-offs

Cover trade-offs between context size, inference speed, cost, and task performance. Larger contexts enable tasks like long document summarization but may be overkill for simple tasks.

5. Implementation strategies

Mention approaches like sliding window attention, positional interpolation, and memory-efficient attention to handle larger contexts without prohibitive costs.

Key Points to Mention

  • Quadratic attention complexity with sequence length
  • Memory and compute requirements for KV cache
  • Need for training/fine-tuning on longer sequences
  • Techniques like sparse attention, sliding window, and positional interpolation
  • Impact on latency and cost
  • Trade-offs between context size and task suitability

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