KV-Cache Hit Rate Is the #1 Production Agent Metric: Prefix Caching Yields 60-85% Hit Rates on Agent Loops, Cutting Per-Call Cost 5-12x

Agentic Design Patterns·medium signal

Multiple production sources (Manus blog, agentic-design.ai, llm-d.ai) converge on KV-cache hit rate as the single most important metric for production AI agents. Technique: structure prompts so system instructions and static context share a common prefix across turns; use prefix caching to get 85-95% cost savings on hits. Agent loops achieve 60-85% hit rates. Key pitfall: standard load balancers scatter requests across pods, destroying cache locality — use session-affinity routing instead.