Filed under llm-infrastructure.

The Five-Minute Window

In March 2026, Anthropic silently reduced Claude's prompt cache TTL from one hour to five minutes — no blog post, no deprecation notice, no API version bump. For production workloads designed around the longer window, effective costs rose 30–60%. The change was not a bug; it was a vendor adjusting to its own cost curve after measuring what prefix caching at scale actually costs.