Anthropic says Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads and up to 45% less for highly agentic work (Zac Hall/9to5Mac)

Anthropic has released its latest AI models, Fable 5.1 and Mythos 5.1, which the company claims are its most capable large language models to date. According to Anthropic, Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads and up to 45% less for highly agentic work.

The two models are technically identical but come with different guardrails, with Fable 5.1 being broadly available and Mythos 5.1 reserved for vetted partners working in cybersecurity and life sciences. Fable 5.1 has set records across several AI benchmarks, including Terminal-Bench-Science 0.1 and Terminal-Bench 4.0.

Anthropic also claims that Fable 5.1 has more relaxed guardrails, allowing researchers to use it to discover software vulnerabilities, although support for more advanced tasks is only available in Mythos 5.1, according to SiliconANGLE. The company says its updated biology safeguards now fire far less often on benign medical questions, and that cybersecurity safeguards produce about 60 percent fewer false interventions in Claude Code sessions than before, as per Mashable.

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