Anthropic has launched Claude Fable 5.1 and Claude Mythos 5.1, describing them as its most advanced models for coding and knowledge work. The new generation significantly outperforms previous Claude models and leading competing systems across several published benchmarks covering scientific research, coding and professional tasks.
On Terminal-Bench-Science 0.1, Fable 5.1 scored 52.6%, compared with 29.0% for Claude Opus 5 and 22.4% for GPT-5.6 Sol. Fable 5.1 also achieved 55.8% on Terminal-Bench 4.0, while the less restricted Mythos 5.1 reached 60.9%.
Both versions use the same underlying model but differ in safeguards. Fable 5.1 is generally available, while Mythos 5.1 is restricted to trusted-access programs focused on areas including cybersecurity and life sciences. Fable 5.1 supports a 1 million-token context window and up to 128,000 output tokens.
