A fresh timestamp, request ID, or path at the top of your prefix is never byte-identical twice, so every new session misses the cache. Rewrite those volatile fields to stable placeholders and restore them out of band, turning cold pre-fills into cache hits.
Rewrite Volatile Prefix Fields to Placeholders So Cold Starts Hit the Cache
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More in Prompt Caching & Reuse
Freeze the Prefix: One Stray Timestamp Kills Your Whole Cache
Prompt caching is a prefix match. A single dynamic byte near the top of your prompt silently invalidates everything after it, so you pay full price every call without realizing it.
Share One Cached System Prompt Across All Your Users
A single per-user byte (name, ID, locale) in the system prompt forks the cache into one entry per user. Strip personalization out of the prefix so every user reads the same cached block.
Cache Your Tool Definitions, Not Just the System Prompt
Tool schemas render before the system prompt, so a non-deterministic tool list silently blocks the cache for everything after it. Sort and freeze the tool array to make tools cacheable.