Building a great AI agent isn’t just about choosing the right models. The harness is the architecture surrounding the model. How it renders context, executes... Building a great AI agent isn’t just about choosing the right models. The harness is the architecture surrounding the model. How it renders context, executes actions, manages state, and decides when a task is done shapes outcomes just as much as the model itself. Harness design alone can account for double-digit swings in benchmark results and significant differences in token cost… Source