You're Optimizing the Part of Your Agent You Don't Own

Short summary

Teams waste effort optimizing the model — the part they rent and can't change — when the harness around it is the bigger lever. LangChain moved a coding agent from rank 30 to top 5 through scaffolding alone. The evolution runs from prompt engineering to context engineering to harness engineering, where you manage the loop, tools, roles, and evaluation as a decoupled system treating the model as a replaceable component.

• •The harness (scaffolding around the model) is a bigger performance lever than the model itself
• •Evolution: prompt engineering → context engineering → harness engineering
• •Key patterns: reduce-offload-isolate for context, external evaluator loops, decoupled brain-hands-session architecture

Generated with AI, which can make mistakes.