Anthropic Investigates Unauthorized Access to Mythos AI Model

Anthropic has positioned Claude Mythos 5 as its most powerful cybersecurity model, making its capabilities and access controls consequential for critical infrastructure protection and AI governance. With the public-facing Fable 5 still blocked, the gap between government and civilian access to advanced models has fueled controversy over technological monopolies and double standards.

Anthropic recently announced that Mythos 5 had been cleared to come back online, but only for certain US critical infrastructure organizations, with no access for the general public. Fable 5 remains blocked. Anthropic did not disclose the exact announcement date, the number of authorized organizations or any financial amounts involved, prompting criticism from the online and open-source communities that it is using AI risks to entrench national and technological advantages.

Anthropic's Mythos and Fable are AI models designed for advanced reasoning and cybersecurity tasks. The tests involved the defenses of classified U.S. National Security Agency networks. A model capable of quickly identifying weaknesses in national-security systems could affect AI safety governance, government procurement and the Five Eyes alliance's plans for technological sovereignty. As of July 19, 2026, no publicly disclosed amount was associated with the matter.

Recent reports said Mythos penetrated NSA systems within hours during a government red-team test, prompting U.S. lawmakers to call for mandatory third-party testing. Foreign media later clarified that the test took place in a simulated environment and did not involve an actual intrusion into the NSA's classified networks. The U.S. government has also restricted accounts belonging to non-U.S. nationals from accessing Mythos and Fable. As of July 19, 2026, officials had not disclosed the test date, full results or the date the restrictions took effect.

Anthropic has introduced Claude Mythos, also known as Fable 5, touting stronger code-analysis and vulnerability-detection capabilities. Such models can help defenders patch smart contracts but may also lower the technical barriers to launching cyberattacks, fueling concerns in the crypto community about the security of assets and protocols.

Anthropic said the new model includes general-purpose safety safeguards and routes cybersecurity-related queries to a specialized model to reduce the risk of misuse. The Uniswap founder, however, criticized the design of its “safety filter” as poorly calibrated. Related reports did not disclose the exact release date, any losses or the value of assets affected.

macOS isolates applications through kernel permissions and multiple layers of security. If those protections are bypassed, attackers could gain elevated system privileges. Cybersecurity research firm Calif combined Anthropic’s internal Mythos AI model with human experts to analyze the system, underscoring generative AI’s growing ability to tackle complex vulnerability research.

In 2026, Calif’s team had Mythos identify a way to bypass macOS security protections and uncover a privilege-escalation vulnerability within five days. The flaw was subsequently designated CVE-2026-28952 and affects the macOS 26.5 kernel. Apple has received the report and begun verification, while the related acknowledgments also credit Anthropic’s Claude with discovering the vulnerability.

Anthropic is developing its flagship Claude Mythos model with advanced coding, reasoning and autonomous cybersecurity capabilities. Its ability to rapidly chain vulnerabilities together could lower the barrier to cyberattacks, making the leak more than a product-secrecy issue. It also raises concerns about zero-day exploitation, responsible disclosure mechanisms and the defense of critical infrastructure worldwide.

As of July 19, 2026, Anthropic was investigating unauthorized access caused by a system configuration error. Reports said vulnerabilities could be attacked within as little as four hours of disclosure. The company is not making Mythos broadly available for now, instead prioritizing trials by cyber defense organizations and addressing risks through its Glasswing program and threat-intelligence sharing.

Anthropic’s Mythos AI model is positioned as a system with advanced cybersecurity capabilities. But its powerful offensive and defensive tools could also be misused, drawing scrutiny from the European Commission and financial regulators. Anthropic has pledged to comply with the EU’s AI Code of Practice, assess the model’s risks and take steps to mitigate them.

EU officials have now met with Anthropic for a briefing on cybersecurity concerns surrounding Mythos, while euro-area finance ministers have separately raised requirements concerning bank access. Available information does not disclose the exact date of the meeting, the number of banks affected or any transaction amounts. Attention will now turn to access permissions and risk-control standards.