Anthropic launches Claude Fable 5.1 and says it’s up to 45 percent cheaper for agentic work

Anthropic has launched its latest AI models, Claude Fable 5.1 and Claude Mythos 5.1. The two models are effectively the same, but with different guardrails. Fable 5.1 is broadly available, while Mythos 5.1 is restricted to vetted partners working in cybersecurity and the life sciences.

According to Anthropic, Fable 5.1 offers stronger performance than its predecessor, Fable 5, at a lower cost. The company claims typical workloads will cost around 25 percent less, with savings of up to 45 percent for complex agentic tasks. This is largely due to cheaper cache-read pricing.

The new models also feature a statistical signature or watermark embedded in their generated text, which can provide evidence that Claude was involved in writing or processing the text. However, this watermark is not applied when a particular token is required for accuracy, such as in code generation. Additionally, Anthropic says it has updated its safety and alignment procedures, including more precise filters to reduce false interventions.

For example, cybersecurity safeguards in Claude Code sessions produce about 60 percent fewer false interventions than before.

Brief written by urgent.news from The Verge, The New Stack, Techmeme, SiliconANGLE, Mashable — 5 reports on this story. Machine-written — may contain errors; check the original before relying on it.