Under the hoodTier: how much it should matter to you
2Useful: my rating, 1 to 5
3Signal: worth watching, 1 to 5
Prompt CachingArea: what it touches
Internal ChangesKind: in v2.1.300,
Internal ChangesSection of the release
What
Claude Code can cache parts of a request, so repeated text does not have to be processed again. A TTL (time to live) is how long that cached copy is kept. The usage data Claude Code sends after each successful request already recorded the cache TTL and the reason for it. It now also records prompt_cache_messages_ttl, a separate TTL for the conversation messages in the cache.
Why
In practice this points to messages possibly having their own cache lifetime, separate from the rest of the request.
