LLM Prompt Caches Expire Fast – 4‑Minute Keepalive Beats 30‑Second Pings
Prompt caches shave latency and cost, but their TTL varies wildly: Anthropic drops after ~5 min, OpenAI after ~10 min, and Google after ~15 min. A 30‑second keepalive ping wastes up to eight‑times more money, while a 4‑minute interval saves on Anthropic and avoids needless traffic on others.