OpenAI added a 12-hour prompt cache to the Responses API on 2026-10-20
(prompt_cache_options.ttl "12h", GPT-5.6 and later). A 12-hour write
costs 2.5x the input price, twice the 30-minute write. We already
forwarded the option but billed every cache write at the 30-minute price.
- Read cache_write_tokens_details from Responses usage and keep the split
through streaming, compaction and format conversion.
- Ratio pricing bills 12-hour writes at twice the cache write ratio, the
same way Claude 1-hour writes use 6/3.75.
- Expressions get a cc12h price. When an expression leaves the long-lived
price out, 12-hour writes cost twice the cc price and Claude 1-hour
writes 6/3.75 times it; without a cc price they bill as input. Claude
cache writes are no longer free when an expression omits cc or cc1h.
- gpt-6-astra prices 12-hour writes at $25 ($50 above 272K tokens).
- GPT models with a cache write ratio convert to expressions with cc12h.
- Chat Completions forwards prompt_cache_options.
- The pricing editor, cost estimator, pricing pages and usage log details
show the 12-hour price and tokens.
Calcium-Ion
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