Your LLM Agent's Prompt Cache Is Silently Broken — A 571-Project Study Found the Bill
Your LLM Agent's Prompt Cache Is Silently Broken — A 571-Project Study Found the Bill You switched on prompt caching, watched your LLM bill drop, and moved on. The dashboard still shows cache hits. The answers still look right. So why does the invoice keep creeping up? A new study of real agent codebases has an uncomfortable answer: the most common caching bugs don't break anything visible. They just quietly stop saving you money — and in some cases, they lie to you about how much you saved. What the researchers did The paper is "Silent and Costly: Characterizing and Detecting Prompt-Caching Mis-Integration in LLM Agents" by Ying Zhang, Ruoqi Guo, Yi Liu, Gelei Deng, Yuekang Li, Yepang Liu, and Leo Zhang, submitted to arXiv on 26 October 2026 and accepted at ICSE 2027. It is the first empirical study of how prompt caching actually goes wrong in downstream applications — not in theory, but in shipped code. The team examined 120 prompt-caching-related pull requests from...