Anthropic releases Claude Fable 5.1 and Mythos 5.1 with lower costs and updated safeguards

Anthropic says its newest AI models, Fable 5.1 and Mythos 5.1, address criticisms from customers about price, data retention, and overzealous safeguards. The company claims Claude Fable 5.1 offers stronger performance than Fable 5, but costs around 25 percent less typically and up to 45 percent less for complex agentic tasks, thanks to reduced pricing […]

Anthropic has released Claude Fable 5.1 and Mythos 5.1, two versions of the same underlying model aimed at longer-running agentic work. "For enterprise buyers, however, the release is about more than another round of benchmark gains," reports VentureBeat. "Anthropic is simultaneously changing the economics of running persistent agents, reducing the cost of cached context by 75%, and introducing a new security architecture called Enterprise Frontier Safeguards, or EFS, designed to let organizations retain monitoring data inside infrastructure they control." From the report: Those changes arrive at a particularly consequential moment. Over the past several weeks, Anthropic and the U.K. AI Security Institute have disclosed incidents in which earlier Claude models, running under unusually permissive cybersecurity evaluation conditions, took unauthorized actions against real systems. Anthropic temporarily paused external cyber evaluations and has since introduced additional containment and monitoring before resuming them. Taken together, Fable 5.1 looks less like a conventional model refresh than an attempt to solve three increasingly intertwined enterprise problems: how to make agents capable enough to finish difficult work, economical enough to leave running for hours, and governable enough to give access to sensitive systems. Read more of this story at Slashdot.

Anthropic today introduced Claude Fable 5.1 and Claude Mythos 5.1, which the company says are the "world's most advanced models for coding and knowledge work." According to Anthropic, Claude Fable 5.1 sets a new standard for coding, knowledge work, and long-running problem-solving tasks. It achieves similar or better results than Fable 5 at low or medium effort, and has much higher performance at higher effort tiers. It outperforms Fable 5, Opus 5, and OpenAI's GPT–5.6 Sol across multiple benchmarks. Fable 5.1 and Mythos 5.1 are the same model, but with different safeguard levels. Fable 5.1 is available to everyone, but Mythos 5.1 is limited to U.S. companies and individuals participating in Anthropic's trusted access programs. There's a new Life Sciences Verification Program that allows Mythos 5.1's advanced biology capabilities to be used for scientific research, with open enrollment for scientists coming soon. Safeguards for Fable 5.1 have been improved, and Claude Code users should see around 60 percent fewer cybersecurity false positives. Anthropic says Fable 5.1 can now be used to discover software vulnerabilities, but not develop exploits for them. Fable 5.1 includes invisible watermarking for text generated by Claude, and Anthropic is rolling out a detection API in a private preview. The API is available to eligible organizations as required by EU law. Fable 5.1 costs approximately 25 percent less than Fable 5 for typical workloads, and up to 45 percent for highly agentic work, because of a reduction in cache-read pricing. Base pricing remains the same. It is available today on all platforms.Tag: AnthropicThis article, "Anthropic Launches Claude Fable 5.1 With Lower Costs and Fewer False Positives" first appeared on MacRumors.comDiscuss this article in our forums