# Prompt caching

Band: established — Settled. Documented by a primary source and not seriously disputed.
Group: The harness

Reuse of an already-processed context prefix, billed at a fraction of fresh input. It makes the front of a context expensive to change and the back cheap to extend, which is why appending to a file the agent has already read costs less than rewriting its top. Most of the advice about keeping instructions stable is really an economic argument wearing a quality costume.

## See also

- [MCP (Model Context Protocol)](https://clickai.dev/legend/mcp)
- [Context load / cognitive load](https://clickai.dev/legend/context-load)
- [Handoff artifact](https://clickai.dev/legend/handoff-artifact)

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