Architecting Hallucination Out of RAG Systems: Making Refusal Structural, Not Aspirational

Prompt-based guardrails fail because language models prioritize helpfulness over truthfulness under retrieval uncertainty. This article demonstrates how treating refusal as an architectural property—filtering low-confidence results before the model sees them—makes hallucination structurally impossible rather than behaviorally requested. For fast-evolving libraries like MCP SDK with breaking API changes, this design pattern also solves version consistency by tagging and filtering corpus chunks, ensuring retrieved snippets won't blend incompatible versions.