INT4 KV-cache quantization keeps RAG answers correct while silently ungrounding them.

Auditing Qwen2.5-7B-Instruct on RGB and HotpotQA with a hallucination detector, NLI entailment and an LLM judge, INT8 is near-lossless on accuracy and faithfulness (arXiv 2608.30996). INT4 lowers accuracy, and among answers that stay factually correct, over 90% of faithfulness changes are negative. Accuracy metrics are blind to that regression. The harm grows with noisier retrieval and more retrieved chunks, so compressing precomputed caches to save storage needs a faithfulness audit and not just an accuracy check.