How does prompt caching behavior change when migrating to Claude Sonnet 5?

Prompt caching itself remains a supported feature on Sonnet 5, carried over unchanged from Sonnet 4.6 as part of the broader feature parity between the two versions.

What does change is the underlying token counts: because Sonnet 5's new tokenizer maps the same text to a different number of tokens than Sonnet 4.6's tokenizer did, cached token counts for a given prompt will differ between the two models even if the prompt text itself is byte-for-byte identical.

The practical implication is that cache breakpoints and minimum-length thresholds sized against Sonnet 4.6 token counts need to be re-verified against Sonnet 5's actual token counts, rather than assumed to carry over directly, since a prompt's token length relative to any caching threshold can shift purely from the tokenizer change.

Invest now in Acorns!!! 🚀
Join Acorns and get your $5 bonus!

Acorns is a micro-investing app that automatically invests your "spare change" from daily purchases into diversified, expert-built portfolios of ETFs. It is designed for beginners, allowing you to start investing with as little as $5. The service automates saving and investing. Disclosure: I may receive a referral bonus.

Invest now!!! Get Free equity stock (US, UK only)!

Use Robinhood app to invest in stocks. It is safe and secure. Use the Referral link to claim your free stock when you sign up!.

The Robinhood app makes it easy to trade stocks, crypto and more.

Webull! Receive free stock by signing up using the link: Webull signup.