Anthropic announced Claude Fable 5.1 and Claude Mythos 5.1, its latest AI models aimed at coding, knowledge work and scientific research. The company says Fable 5.1 offers stronger performance than its predecessor while costing less for typical workloads.

Fable 5.1 is available to all users through Anthropic’s services and developer platforms. The model can also be accessed through Amazon Web Services, Google Cloud and Microsoft Azure, as well as the Claude API.

Anthropic says Fable 5.1 could be around 25% cheaper than Fable 5 for typical token-based workloads. For highly agentic tasks, the company estimates savings of up to 45%. Lower cache-read costs are the main factor behind the reduction.

The company also claims that Fable 5.1 handles longer-running tasks more effectively. It is designed to take fewer shortcuts that could reduce the quality of its output.

Anthropic pointed to testing at investment firm Millennium as one example of the model’s capabilities. According to the company, Fable 5.1 helped identify the source of a rare crash in Millennium’s internal systems. Engineers and other AI models had previously struggled to determine the cause.

Claude Mythos 5.1 is based on the same model as Fable 5.1. It has different safeguards and is being distributed through restricted access programmes.

The model is currently available to approved cyber defenders and life scientists through Anthropic’s Cyber Verification Program and Life Sciences Verification Program. Access is currently limited to selected US organizations.

Anthropic said it is working with the US government to expand Mythos 5.1 access to more domestic and international partners.

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