Claude Fable 5 caught bugs GPT-5.5 and Opus 4.8 missed, then the US government forced it offline
… Fable 5 scored 80.3% on SWE-Bench Pro, 11 points ahead of GPT-5.5. On Cognition's FrontierCode Diamond benchmark , which tests whether models can handle difficult coding tasks to production-codebase standards, it scored 13.4% to GPT-5.5's 6.3%. …