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Anthropic launches Claude Fable 5.1
Anthropic says the new model more than doubles its predecessor on a scientific-agent benchmark and costs around 25% less to run. Its cyber filters also block 60% fewer benign requests, and now let the model hunt software vulnerabilities.
Edited by Trevor Brown · Sep 1, 2026 · frontier labs
Anthropic released Claude Fable 5.1 and Claude Mythos 5.1 on September 1, an update to the model line it pulled off the market for close to three weeks in June.




