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Design a streaming text-moderation system that blocks toxicity, PII, and prompt injection within 50ms p99.

Fifty milliseconds at p99 to catch toxicity, PII, and injection on every message. An LLM in the hot path blows the budget. The strong answer tiers the checks and keeps the LLM off the critical path.

Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.

Fifty milliseconds at p99 to catch toxicity, PII, and injection on every message. An LLM in the hot path blows the budget. The strong answer tiers the checks and keeps the LLM off the critical path.

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