Production traces show 14 eviction policies barely beat LRU for agentic prefix caches.

arXiv 2609.28870 replayed production agentic traces from two companies against 14 algorithms in both HBM-constrained and large-pool settings. The sophisticated policies give little over LRU despite a large gap to Belady, and the cause is structural: active sessions resend growing context at a regular pace, making recency unusually predictive. Their recommendations are keeping LRU as the base and adding quick demotion for one-hit prefixes, compute-aware partial eviction for expensive misses, and capacity-dependent granularity. Traces and simulator are promised.