DictionaryCaching
Cache Read
The discounted price for reusing text the AI service already stored, often a tenth of the normal price or less.
Definition
The cost of using a previously cached prompt prefix. Cache reads cost 0.1x base input on most Claude models, 0.05x on Claude Opus 5.5 and Sonnet 5.5 (Sonnet 5.5: $0.10/MTok vs. $2/MTok), and 0.025x on Claude Fable 5.1 and Mythos 5.1. The break-even point depends on how many times the cached prefix is reused.
Example
Rereading a cached 100K-token prefix on Claude Sonnet 5.5 costs $0.01 (at $0.10/MTok) instead of $0.20.