HarnessTax: How Much Does the Harness Matter for Coding Agents? harnesstax.github.io ↗

Berkeley researchers tested 21 model-harness pairs on SWE-bench Lite and Terminal-Bench. Harness barely moves success rate but can double the cost: Claude Fable 5 solves about the same share of tasks in Claude Code as in Pi, a minimal open harness, at twice the price.