Three months after the launch of Fable 5, Anthropic has recently released two new AI models, Claude Fable 5.1 and Claude Mythos 5.1. The new models sit above Anthropic’s other models — Haiku, Sonnet and Opus — which the company classifies as small, medium and large models. Fable 5.1 and Mythos 5.1 are based on the same underlying model but have different safety controls. Fable 5.1 is available to all users, while Mythos 5.1 is restricted to approved users working in cybersecurity and life sciences.
According to Anthropic, Fable 5.1 is its strongest model so far for coding, research and problem-solving. In the Terminal-Bench-Science 0.1 test, it scored 52.6%, compared with 24.7% for Fable 5, 29.0% for Opus 5 and 22.4% for rival model GPT-5.6.
Anthropic is also introducing Enterprise Frontier Safeguards (EFS), a system designed to allow business customers to keep their data on their own servers rather than Anthropic’s infrastructure. The company says this will provide greater control over sensitive data while maintaining safeguards against misuse.
EFS will be introduced in stages from autumn 2026 across services and platforms including Claude Code, Claude Enterprise, Amazon Bedrock, Google’s Agent Platform and Microsoft Foundry.
Until the system becomes available, eligible customers can use Fable 5.1 with no data stored at all, according to Anthropic.
The company has also improved its safety checks, saying it has reduced false alarms in cybersecurity by 60%. Fable 5.1 can also be used to identify software security vulnerabilities, although it is not designed to exploit them.
See What’s Next in Tech With the Fast Forward Newsletter
Tweets From @varindiamag
Nothing to see here - yet
When they Tweet, their Tweets will show up here.
