Claude Fable 5.1 and Mythos 5.1 are the same underlying model but with different safety levels: Fable is available to everyone, while Mythos has fewer restrictions and is limited to trusted access programs for cybersecurity and life sciences.
Fable 5.1 brings major improvements in coding, research, and long-running tasks while becoming up to 45% cheaper for highly agentic workloads. It can now also help discover software vulnerabilities, with Anthropic saying its updated safeguards trigger 60% fewer false positives in cybersecurity.
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