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Interview question · LLM Application Security

Should LLM guardrails fail open or closed, and how do you handle their latency and cost?

There is no single answer, and saying so is the start. The scored answer decides per check from what its failure would let through, and designs the latency budget so the choice is rarely forced.

mediumNewPreparation tags: Amazon, Microsoft, GoogleUpdated Nov 2026

There is no single answer, and saying so is the start. The scored answer decides per check from what its failure would let through, and designs the latency budget so the choice is rarely forced.

Make your first attempt

What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

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What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

The guardrail service in front of an assistant times out during a traffic spike. The on-call engineer must decide what the app does when it cannot get a verdict.

  1. What happens if the assistant fails open?
  2. What if the assistant can take actions such as refunds or emails?
  3. What if it only answers general product questions?
  4. What if the guardrail is slow rather than down?
  5. How would you know it failed open in production?
  6. How would you set the policy?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Premium opens every answer and ladder.

UP NEXT ON YOUR JOURNEY
Next in this trackHow do you evaluate guardrails honestly, without optimising only for pass rate?Next in this trackCan prompt caching or response caching in an LLM application leak data between users?Next in this trackWhat security and privacy issues come with fine-tuning a model on customer data?
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