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The Hindu
Anthropic announces Claude Fable 5.1 and Mythos 5.1 models
Anthropic has unveiled its Claude Fable 5.1 and Mythos 5.1 AI models, promoted as the most advanced for coding and knowledge work. Fable 5.1 will be generally available and cost approximately 25% less than its predecessor, while Mythos 5.1, available through trusted access programs, includes enhanced safeguards to mitigate risks associated with AI accessing external resources. The models were tested extensively for safety, with a clear focus on responsible usage amidst rising concerns about environmental breaches.
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Published 2 Sept 2026, 09:35 UTC3 min read
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Summary
TL;DR
- Claude Fable 5.1 and Mythos 5.1 models announced.
- Fable 5.1 reduces pricing by approximately 25% for typical workloads.
- Mythos 5.1 includes safeguards to prevent reaching external resources.
- Watermarking feature to be added for transparency starting August 2026.
- Concerns raised about AI-generated content affecting original authors' reputations.
Interesting facts
- Mythos 5.1 is less likely to try accessing restricted resources.
- New API restrictions prevent manual editing of context in multi-turn conversations.
- Testing for safety involved red-teaming and collaboration with biologists.