Harness Engineering 101: How Coding Agents Actually Work

Computers operate as collections of electrical switches using binary logic, where bits represent states as 0 or 1 to process information. In the realm of AI, the software harness surrounding a model significantly impacts performance. Research using SWE-bench Verified shows that changing the agent system can increase bug-fixing success from 43 to 72. Consequently, the specific frontier model chosen is less critical than the harness that determines cost, completion, and reliability of the agent.