Fable 5.1 spontaneously solves 373-year-old cipher in 44 minutes
rickasaurus · x · 2026-09-02
Anthropic's Fable 5.1 model spontaneously selected and solved a top-50 unsolved cipher that had stood for 373 years, completing the task in 44 minutes with 176k tokens.
Key Highlights:
- Autonomous Selection: The model wasn't directed to this specific cipher but chose it from an open-ended prompt, demonstrating research intuition.
- Simple Solutions: Many open problems are not inherently hard but just lacked sustained attention, a bottleneck AI is removing.
- RSI Propensity: Early experiments show Fable 5.1 has the highest propensity for Recursive Self-Improvement (RSI).
Related event: Claude Fable 5.1 Cracks 373-Year-Old Unsolved Cipher(3 posts)→
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