Stop Prompt Injection in Production: A Multi-Layer Defense for Healthcare, Finance, and Government AI Systems

TL;DR Prompt injection is the LLM security threat in 2026, with attack success rates above 90% against unprotected systems. Regex blocklists fail. LLM-based detectors fail. The only thing that has held up across healthcare, finance, and government deployments is a multi-layer validation pipeline that does NOT depend on another LLM to police user input. This post is the practitioner version of a longer piece I wrote on Medium for Towards AI. Full code, three real incident write-ups, and the full architecture are in the original. Linking it at the bottom.