Asked about The cost maths, and caching whole responses
When does prompt caching not save money?
An answer that works
When requests are too infrequent for the cache to stay warm, so most requests pay the write price, or when the prompt changes near the start so the prefix rarely matches. Work out the numbers from your real traffic before assuming a saving.
Then they push further
How would you confirm the saving in production?
Read the cached and uncached token counts the API reports for each request, compute the hit rate and the effective price per request, and compare with the month before.
What gets marked up
Strong answers reason from traffic pattern and prices, not from 'caching is always cheaper'.
Reading an answer is not being able to give one. The section that teaches this is The cost maths, and caching whole responses, 4 hours of Prompt caching.
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