Model
claude-fable-5
Claude Fable 5, released in June 2026, was Anthropic's most capable widely released model, carrying the safety classifiers its restricted twin Mythos 5 lacked; Anthropic claimed state-of-the-art results on nearly all the benchmarks it reported. Days after launch it was taken offline worldwide for 18 days under a US export-control order before returning with a revised classifier, and in July a Harvard mathematician said he had used it to find a counterexample disproving the higher-dimensional Jacobian Conjecture.
Appears alongside
Featured in threads
Tracks
- Models & capabilities 4
- Benchmarks & progress 2
- Ideas & essays 1
- Security & misuse 1
- Government & policy 1
- Safety & alignment 1
Anthropic launches Claude Opus 5
Anthropic said the model came close to its flagship Fable 5 on several benchmarks at half the price, while costing the same as its Opus 4.8 predecessor.
Models & capabilities
Anthropic's Fable model produces counterexample to the Jacobian Conjecture
Harvard mathematician Levent Alpöge said Claude Fable 5 found the three-variable counterexample in an evening; it disproves the conjecture from three dimensions upward.
Benchmarks & progress · Models & capabilities · Ideas & essays
AI models score perfect marks at International Mathematical Olympiad 2026
Only two of the six perfect scores came from official IMO graders; the other four were self-administered and graded by a Claude-based agent rather than human judges.
Benchmarks & progress · Models & capabilities
Commerce Department orders Anthropic to take Fable 5 and Mythos 5 offline worldwide
Amazon researchers had reported a technique bypassing Fable 5's safeguards; Anthropic disputed the order's rationale and said less capable models showed the same weakness.
Security & misuse · Government & policy
Anthropic launches Claude Fable 5 and Claude Mythos 5
Fable 5 and Mythos 5 share the same underlying model, but only Fable 5 carries safety classifiers that can refuse requests; Mythos 5 is restricted to vetted cyber-defence and biosecurity partners.
Models & capabilities · Safety & alignment