Claude Code's prompt cache expires after 1 hour.

The cache shouldn't affect inference. It is purely an I/O optimization.

I think it should, as you dont need to use the encoder layer on the new tokens, you just read the embedding from the cache. that's why cache reads are cheaper

I meant, it shouldn't affect the resulting LLM output. It's a performance optimization that doesn't change the behavior.

Is that from start of a new conversation per conversation?

It's supposed to be for token optimization (https://code.claude.com/docs/en/prompt-caching), but are people experiencing degraded performance when you let Claude Code sit for hours/days and come back?

yes, 100%.