Claude Fable 5.1 (Adaptive Reasoning, Low Effort, Default Fallback)

Claude Fable 5.1 is an AI model developed by Anthropic and released on September 1, 2026. This model features adaptive reasoning capabilities with low effort and default fallback settings. In terms of performance metrics, it achieves an intelligence index of 58.1 and a coding index of 75.2. Benchmark results for the model include a GPQA score of 0.881, an HLE score of 0.489, a SciCode score of 0.557, and an LCR score of 0.793333333333333. Regarding operational speed, the model provides an output speed of 42.912 tokens per second with a time to first token of 2.639 seconds. Pricing is structured at $10.00 per million input tokens and $50.00 per million output tokens, resulting in a blended rate of $20.00 per million tokens.