Claude Sonnet 5.5 prompt-cache reads drop to $0.10 per million tokens, while cache writes and all other prices stay put
Synopsis
In its Claude Platform release notes, Anthropic cut the price of prompt cache reads on Claude Sonnet 5.5 from $0.20 to $0.10 per million tokens, which is 0.05x the base input price instead of 0.1x. Cache writes and all other prices are unchanged. For developers who resend the same long prefix, the saving applies to re-reading the cache, not to the first write or to newly generated content.
Interpretation
Prompt cache reads on Claude Sonnet 5.5 are half as expensive, falling from $0.20 to $0.10 per million tokens. Cache reads previously cost 0.1x the base input price and now cost 0.05x. The same update states that cache writes and all other prices are unchanged, so the change lands only on cache reads.
Prompt caching lets a repeated prefix avoid being billed as fresh input each time, and the read of that cached prefix is billed at the discounted rate. A cache read is the step that reads a stored prefix, and it is priced separately from writing the cache. The price change names Claude Sonnet 5.5 specifically and gives both a dollar rate per million tokens and a multiplier of the base input price.
Perspective
The adjustment covers prompt cache reads on Claude Sonnet 5.5 only; cache writes and all other prices remain as stated.
The update does not say whether the price applies to other models or platforms, and it gives no measured cost savings.