New Leaders in Programming and Science: Anthropic Presented Claude Fable 5.1 and Mythos 5.1
Anthropic says the models cut cache read costs by 75% and deliver stronger coding and research performance than Opus 5.
- Anthropic released Claude Fable 5.1 and Claude Mythos 5.1 on Tuesday, its most powerful models to date, sharing identical underlying weights but differing in safeguard configurations.
- The new models succeed the Fable 5 and Mythos 5 line released earlier this year, supporting a 1-million-token context window, 128,000-token maximum output, and always-on adaptive thinking.
- Benchmark results show Fable 5.1 scoring 52.6% on Terminal-Bench-Science, more than double its predecessor's 24.7%, while cache read costs dropped 75% to $0.25 per million tokens.
- Cognition announced it would move all Opus 5 traffic in its Devin product to Fable 5.1 on launch day, while Jane Street Capital noted the model "remains readable over long, multi-step tasks."
- Anthropic added invisible statistical watermarking to comply with the Act, while introducing Enterprise Frontier Safeguards to enable private model usage for regulated industries starting fall 2026.
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46 Articles
Anthropic Announces Claude Fable 5.1 And Mythos 5: Here’s What They Offer
Claude Fable 5.1 is now available to the public, while Mythos 5.1 is limited to select customers through Anthropic’s verification programmes. Both use the same core system but have different safety restrictions. Mythos 5.1 is designed for approved organisations working in cybersecurity and life sciences. It provides access to capabilities that are more restricted in the standard version.
Anthropic’s Fable 5.1 and Mythos 5.1 bring improved coding and research capabilities
The new AI models could help users handle complex coding tasks, research problems and knowledge work more efficiently, while offering improved performance and more precise safety safeguards.
Anthropic presents Claude Fable 5.1 and Mythos 5.1, specialized in code development and AI applied to science
Anthropic Launches Fable AI Models: High Performance, Lower Cost, Fewer Refusals
Anthropic launched Fable on September 1, 2026, a new AI model family offering strong performance at significantly lower prices with fewer content restrictions than predecessors. Available in 1B, 8B, and 70B sizes, it balances helpfulness and safety while reducing unnecessary refusals. This positions Fable as a flexible, cost-effective option for developers and enterprises.
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