The Same Model, Three Agents: Why the Harness - Not the Model - Decides What Your AI Can Do

One-paste order for Medium's new-story editor: title → body → diagrams → notebook link → checklist.

Swap the model in your AI agent and you expect it to get smarter. Swap the harness - the loop, the context manager, the tool interface, the recovery logic - and the same weights score 28% on one benchmark and 49% on the next.

In 2026, the industry finally stopped pretending the model is the agent. The evidence says the wrapper is the variable.

ELI5: the chef