Anthropic Launches Claude 5.1 with Reduced Safeguards and Lower Prices

Key Takeaways

1Anthropic launches Claude Fable 5.1 and Mythos 5.1, based on the same model with differentiated safeguards

2The cost of cache reading drops to $0.25/million tokens, reducing overall costs by up to 45% depending on usage

3Fable 5.1 is available on major clouds and via API, while Mythos 5.1 remains reserved for verified U.S. organizations

Why it matters : This development comes after U.S. restrictions and aims to balance security, performance, and cost control for businesses.

After the suspension imposed by Washington in early summer, Anthropic is reintroducing its 5.x series. Claude Fable 5.1 is now available, while Mythos 5.1 remains reserved for verified U.S. organizations. The publisher announces less intrusive cybersecurity safeguards and a significant reduction in caching costs, while maintaining base rates.

Restricted Access and Return After the U.S. Injunction

A few days after June 9, 2026, the U.S. government required Anthropic to suspend access to Fable 5 and Mythos 5 for all non-U.S. users, regardless of their residence, citing national security. Anthropic implemented this measure while questioning its legitimacy. By the end of July, the company proposed Claude Opus 5, described as a more affordable and less restrictive solution for everyday use. In this context, Mythos 5.1 remains accessible only to U.S. organizations that have been authenticated through the Cyber Verification Program and the Life Sciences Verification Program, the latter established in collaboration with the U.S. government. According to Anthropic, version 5.1 implements more targeted safeguards designed to limit false positives, and Fable 5.1 allows for the detection of software vulnerabilities while preventing the creation of exploits.

Caching at $0.25/million tokens and Savings of Up to 45%

Anthropic announces that it is reducing caching costs to $0.25 per million tokens, a 75% decrease from the previous rate. For regular usage billed per token, the publisher estimates that the overall cost of Fable 5.1 decreases by about 25% compared to Fable 5, with savings of up to 45% on the most intensive agentic tasks. Base rates remain unchanged: $10 per million tokens for input and $50 for output.

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Immediate Availability and New Enterprise Safeguards

Claude Fable 5.1 can be used starting today on various Claude platforms, including via Amazon Web Services, Google Cloud, and Microsoft Azure, and is offered through the API under the name claude-fable-5-1. Anthropic is implementing Enterprise Frontier Safeguards, a data storage solution aimed at providing businesses with complete control over their information while maintaining oversight of malicious usage, with a phased rollout planned starting this fall. For Claude Code, the company reports a reduction of about 60% in security classifier interventions compared to Fable 5. Anthropic also clarifies that Fable 5.1 and Mythos 5.1 share the same model, differentiated by levels of safeguards.

Increased Benchmarks and New Generation 5.1

Anthropic claims a new performance standard for code, knowledge work, and scientific research. The publisher indicates that Fable 5.1 outperforms Fable 5 on tested benchmarks, including Terminal-Bench 4.0 with 55.8% compared to 42% and Humanity’s Last Exam with 60.9% compared to 57.8% without tools. The company has officially launched Claude Fable 5.1 and Claude Mythos 5.1, presented as a new generation of its most advanced model.