Is Cross-Context KV Cache Reuse Always Reliable and Harmless in Agent Execution?

Cross-context KV cache reuse can reduce repeated prefill for reusable agent context, such as skill documents, tool schemas, and policy instructions. However, preserving task success does not necessarily preserve agent execution: KV reused from a different context can substantially alter an agent’s responses and actions, while incurring additional execution costs or unwanted workspace changes even when the task is completed successfully. This paper comprehensively explores the cross-context KV cache reuse mechanism. We trace KV cache reuse from cache differences within model to agent behavior and task outcomes. Further, we characterize how reuse induces behavioral divergence, explain how divergent executions can still preserve task success, and establish a deployment-level criterion for determining when such reuse remains permissible under execution requirements. Overall, this paper identifies and theorizes the impact of cross-context KV cache reuse on agent execution, guiding the reliable deployment of cross-context KV cache reuse in agent systems.