An agent harness is out of the box token efficient because it heavily relies on prompt caching.
But, these best practices are important so that you can actually maintain those savings turn after turn without accidentally breaking the cache.
When building complex multi-agent systems, the harness holds all the heavy lifting: tool definitions, system instructions, and loaded skills.
Without caching, you pay for this massive background context on every single step.
To ensure your setup stays token efficient, structure your context so the cache actually hits:
1) Keep the prefix static:
Caching matches the start of your request. Put core tool definitions and base information at the very top of the context window.
2) Put dynamic data at the end: …



















