HarnessTax: How Much Does the Harness Matter for Coding Agents?

matt_d · hn · 2026-09-17

HarnessTax, a project featured on Hacker News, systematically quantifies how much a coding agent's harness — the scaffolding, tool interfaces, and orchestration around the model — affects benchmark performance versus raw model capability. A useful reference for anyone doing agent evals or attributing gains between model upgrades and harness engineering.

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