Openai just gave prompt caching a debugger. prompt cache diagnostics, out september 8 in the…
openai just gave prompt caching a debugger. prompt cache diagnostics, out september 8 in the responses api, reports why a cached prompt missed its reuse instead of leaving teams to guess.
the cache miss stopped being a mystery.
Context
OpenAI's prompt caching diagnostics documentation says diagnostics are available in the Responses API for GPT-5.6 and later supported models. A request is compared with an earlier response through prompt_cache_options.comparison_response_id, and a reason is reported in prompt_cache_diagnostics when an expected prefix was not reused. Reuse needs an exact prefix match and compatible settings such as model, service tier and tools. Actual reuse is measured by usage.input_tokens_details.cached_tokens, and a Prompt Caching Dashboard monitors across an app.
Setting the comparison id only requests diagnostics. It does not load the earlier conversation or change caching. The documentation is undated and no dated source for September 8 was found, so the release date is unverified. An OpenAI post listed September 22 was not text-inspected. The cache miss stopped being a mystery is the author's take.
Watch next
- The dated OpenAI post.
Sources
- OpenAI docs: prompt caching diagnosticsdevelopers.openai.com
Provenance
The note above is reproduced unedited from the original post, first published on Threads on 22 September 2026 at 23:17 IST. Sources are the papers and datasets the note draws on.
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