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Shieldstral is the 3B safety classifier Mistral released in August 2026: it answers yes or no to a policy written in plain language. Converted to GGUF Q8_0 with llama.cpp and served on a CPU, it blocked no legitimate one among the 100 Spanish and English prompts I prepared, but let 8 of 17 injections through.
A selection of postmortems published between 2025 and 2026 by teams running AI systems in production reveals repeated patterns: guardrail failures, silent model drift, hidden vendor dependency, and a collection of near-misses worth distilling.
Guardrails frameworks promise to filter language-model inputs and outputs to block data leaks, harmful content, or hallucinations. After evaluating four of the most popular ones in production, I cover what they actually do, what latency and billing cost they add, and when they pay off over simpler controls.
