Under the hoodTier: how much it should matter to you
1Useful: my rating, 1 to 5
2Signal: worth watching, 1 to 5
HooksArea: what it touches
Internal ChangesKind: in v2.1.321,
Internal ChangesSection of the release
What
A hook is a command or script you set up to run automatically at certain moments while Claude Code works. When Claude Code registers a hook, it writes a line to its log. If the hook declares breaksPromptCache, that log line now ends with 'uses breakPromptCache'.
Claude Code also records one more internal timing measurement related to hooks.
Why
The prompt cache is how Claude Code avoids resending and reprocessing the same earlier conversation on every turn, which saves time and usage. Hooks can now say that they invalidate that cache, and the log shows which ones do, so you can tell which hook is behind a cache being thrown away.
