AnecdoteArticle

Claude Fable gets too locked into its own frameworks and refuses to reconsider, while GPT-5.6 Sol is willing to adapt and fix problems pragmatically.

Claire recounts a debugging standoff where Fable insisted a broken tool-calling loop was a model limitation, while switching to Codex let Sol fix the same issue on Sonnet 5 in one shot. ✦ AI generated

Claire · Lenny's Newsletter · 2026-07-13 · original ↗

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I had a hardened tool-calling loop in my prototyping product that only GPT-5.5 could run. Fable insisted it was a model problem and refused to budge. The moment I switched to Codex and told it to just fix it, Sol got Sonnet 5 working in one shot.

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✳ Codex ✳ Sonnet 5

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Evidence · 1

Claude Fable 5 wouldn't even proofread this article for me! It insisted on downgrading me to a less capable model.Simon Willison (author) · Simon Willison's Weblog · conf 75%

Counterpoint · 2

GPT-5.6 Sol is very competent but has not struck me as better than Claude Fable 5 for the complex coding tasks I use.Simon Willison · Simon Willison's Weblog · conf 60%When given an open-ended review prompt, Claude Fable 5 wrote 12 scratch scripts and found 4 release blockers plus 10 additional issues, far outperforming GPT-5.5 xhigh in Codex Desktop, which wrote only 5 scripts and found nothing particularly interesting.Simon Willison · Simon Willison's Weblog · conf 60%