A client project convinced one builder the agent harness matters more than the model
alexcovo_eth · x · 2026-07-26
The author says a client project changed his view of which frontier model to use next.
After initially believing in Fable/Opus, he now finds ChatGPT 5.6 Sol High more reliable and performant. He quotes a compliment from Fable 5 High saying ChatGPT’s spec found two missed push-triggering lanes, respected directory-permission constraints, and produced an implementable spec with its own verification checklist.
His main conclusion is that the agent harness matters more than the model choice: he had been using Claude Ccode with Fable/Opus and Hermes-Agent with GPT-SOL-5.6, and the harness itself seems to explain much of the difference.
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