Anthropic releases Claude Fable 5.1, cuts cached token pricing by 75%

Anthropic has introduced Claude Fable 5.1, the latest version of their flagship model, alongside a more restricted edition called Mythos 5.1. Both updates are available via API, cloud platforms, and the Claude desktop app, making their most advanced models more accessible for complex tasks requiring time, sensitive data, and clear safeguards.

Fable 5.1 is the broadly available version, with built-in safety measures that block some high-risk work in cybersecurity and scientific research. Mythos 5.1 has fewer restrictions but requires access through Anthropic's trusted-access program. The main focus is on handling larger assignments, such as software projects, code reviews, troubleshooting, and multistep scientific work.

Anthropic reports significant improvements in various evaluations, including a 55.8% score on Terminal-Bench 4.0 for coding tasks, compared to 42% for the previous version. Mythos 5.1 scores 60.9% under more permissive safety settings, and excels in scientific research with a 52.6% score, more than double the previous version's 24.7%.

The company also lowered the price of cached token reads by 75%, from $1 to $0.25 per million tokens, which can significantly reduce costs for agentic workloads that frequently reuse the same information.