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

Detection is imperfect, so the strong answer is layered: regex with checksums for structured PII, ML/NER for the unstructured PII regex cannot see, and a frank account of why you never rely on redaction alone. Here is the answer.

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