The repeatable part of the request
Many business assistants resend the same instructions, tool definitions, or reference material. Prompt caching can reuse eligible repeated prefixes. The details depend on the provider and model, so verify the current cache requirements before estimating savings.
Structure context deliberately
Keep stable instructions at the beginning and place changing user input later. Do not put timestamps or request-specific identifiers into a reusable prefix unnecessarily. Preserve the meaning of the prompt; cache hits are not valuable if the answer becomes stale or incorrect.
Observe actual behavior
Monitor cached-token usage, latency, and total charges in production. Compare similar requests and account for cache expiry and workload timing. A cache-friendly design can help repeated workloads, but a rarely used workflow may see little benefit.
Keep the security boundary intact
Caching is not permission to reuse private information across customers. Respect data boundaries, provider retention settings, and your own access controls. Re-run your evaluation set when changing prompt structure.