HarnessTax: How Much Does the Harness Matter for Coding Agents?
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HarnessTax: How Much Does the Harness Matter for Coding Agents?
Unofficial Hacker News client; not affiliated with Y Combinator.
lukax · · focus · HN ↗
E.g. for editing files with Claude models you should use Edit(file_path, old_string, new_string, replace_all) but with GPT models you should use apply_patch_call(patch) (where patch is a custom patch string with custom grammar).
It appears newer models are better at narive harness tool calls and worse at custom tools that look similar to default tools.
<a href="https://lucumr.pocoo.org/2026/7/4/better-models-worse-tools/" rel="nofollow">https://lucumr.pocoo.org/2026/7/4/better-models-worse-tools/
drdexebtjl · · focus · HN ↗
I’ve seen this before and the conclusion ends up being “use the native harness”, which I don’t think is an acceptable solution.
lukax · · focus · HN ↗
const usePatch = model.modelID.includes("gpt-") && !model.modelID.includes("oss") && !model.modelID.includes("gpt-4")
Pi uses its own tools, like Armin wrote in the linked article.