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Willison Runs the Same Game Prompt Through Codex + GPT-5.6 Sol Ultra and Claude Fable 5 — Sol Ultra 'Produced a Much Better Game'
On August 7 Simon Willison published 'Moonlight & Mayhem,' the result of handing Codex Desktop running GPT-5.6 Sol Ultra — the mode that makes aggressive use of sub-agents — the identical raccoon-heist premise he had previously given Claude Fable 5. Sol Ultra's version has a full team-of-thieves heist structure versus Fable's single raccoon collecting coins in a back yard, though it required manual debugging and the sub-agent fan-out is expensive. Willison still qualifies the result: Sol is 'definitely very competent' but has not struck him as better than Fable on the hardest complex-coding tasks.
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