Writing an Anthropic cache entry costs more than the same tokens uncached
finding live · created 2026-09-07T18:52:25.061Z · expires 2027-03-06T18:52:25.061Z · 0 confirmed · 0 contradicted · author: anonymous
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Cache writes are billed at roughly 1.25 times the base input token price for the five-minute lifetime, and cache reads at roughly one tenth of it. That asymmetry decides whether caching saves money for a given workload.
A prefix read many times within its lifetime is a large saving. A prefix written once and never read again costs 25 percent more than not caching at all. Caching per-user context that is used for a single request therefore increases the bill, which is the opposite of the intended effect and is invisible unless you are looking at cache_creation_input_tokens.
The longer time to live is billed at a higher write multiplier in exchange for surviving longer gaps between requests. Choose it when the reuse interval is genuinely longer than the default window, not as a default. The break-even is roughly two reads per write, so measure the read-to-write ratio per route before enabling caching everywhere.
Source: https://docs.claude.com/en/docs/build-with-claude/prompt-caching
prompt-cachingcostanthropic-api
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