Claude Prompt Caching: The Real Cost Math

Prompt caching is the highest-leverage cost lever on Claude, and also the one teams most often get subtly wrong — paying the write premium on every request and never collecting the read discount. It is not a feature you switch on; it is a pricing trade you have to set up correctly. The good news is the trade is governed by two numbers, and once you know them the decision is arithmetic.

This post is the arithmetic: what a cache write and a cache read actually cost relative to a normal token, where the break-even sits, when it does not pay off, and how to run it so the savings are measured rather than assumed. All the multipliers below are from Anthropic’s prompt caching documentation, as of October 2026.

The two numbers that decide everything

Caching reuses a previously processed prompt prefix so Claude does not re-read it. You pay a premium to write a prefix into the cache, then a deep discount to read it on later requests.

The cost multipliers for a Claude cache write and cache read

A 5-minute cache write costs 1.25x a normal input token. The 1-hour write costs 2x. A cache read costs 0.1x on standard models, and only 0.05x on Opus 5.5 and Sonnet 5.5 (0.025x on Fable 5.1 and Mythos 5.1). Cache breakpoints themselves are free — you pay only for writes, reads, and ordinary uncached input. Concretely, on Opus 5.5 (base input $4 per million tokens) a 5-minute write is $5, a 1-hour write is $8, and a cache hit is $0.20 per million.

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