Prompt Caching: First vs Repeat Request Costs
Measure prompt-cache cost with a controlled request series: the first request creates or prepares a cached prefix, later requests try to read it, and a control request changes the prefix to force a miss. Compare the usage categories and actual charge for one model. A fixed savings percentage means little without the Model ID, TTL, prefix length, and current prices.
What the experiment measures
Prompt Cache reduces reprocessing of the unchanged portion of the input. This could be a system prompt, a set of instructions, a large document, or a stable story. The question being modified is placed after the general prefix.
The experiment requires three states:
