Function cache_read_multiplier 

pub fn cache_read_multiplier(model: &str) -> f64

Cache-read price as a multiple of the input price (https://platform.claude.com/docs/en/about-claude/pricing, “Prompt caching”). The docs list 0.025× for Fable 5.1 / Mythos 5.1 and 0.05× for Opus 5.5 / Sonnet 5.5; every other model uses the standard 0.1× (also the conservative default for models this table does not know).