How do you detect and redact PII in text at scale (for LLM inputs, logs, and training data)?

Because detection never catches everything, the strong answer works in layers: checksummed regex for structured PII, ML/NER for the unstructured PII regex misses, and an honest explanation of why redaction alone is never enough. Here is the answer.

Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.