- Essays··8 min read
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.
prompt-cachinganthropicapi-economicsllm-infrastructureRead - Essays··8 min read
Cheap hits, confident wrong answers
Prefix caching is deterministic; semantic caching is probabilistic. One is free and lossless, the other can return a confident, well-formatted, wrong answer with an HTTP 200. Both are true in the same architecture diagram.
llm-inferencesemantic-cachingfinopsprefix-cachingRead