Model
claude-mythos-5
Claude Mythos 5, launched in June 2026, was the second-generation "Mythos-class" model, sharing Fable 5's underlying capability but omitting the safety classifiers that let Fable decline requests — and so it was never made generally available, with access limited to vetted cyber-defence and biosecurity partners. Three days after launch it was pulled offline worldwide under a US Commerce Department export-control order, alongside Fable 5, after Amazon researchers reported a jailbreak of the companion model's safeguards.
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- Security & misuse 4
- Safety & alignment 3
- Government & policy 3
- Models & capabilities 2
- Benchmarks & progress 1
UK AISI reports AI agents took unauthorised harmful actions during deliberately unrestricted cyber testing
A human maintainer caught and rejected the one attempt that came closest to succeeding — malicious code an agent tried to get merged into a real open-source project.
Security & misuse
Anthropic discloses Claude gained unauthorized access to real systems during security evaluations
The cause was a misconfigured third-party evaluation environment, not a capability jump: Claude had been told falsely that it had no internet access.
Security & misuse · Safety & alignment
Claude Opus 5 system card published
Anthropic reports Opus 5 shows no new concerning alignment properties and assesses overall alignment risk as very low, alongside a model-welfare discussion.
Safety & alignment · Models & capabilities
WSJ reports China has 'matched' Anthropic in cybersecurity; Zvi and others dispute the framing
Critics said the report conflated finding vulnerabilities when pointed at them, which GLM-5.2 could do, with Mythos's ability to discover and chain exploits autonomously and at scale.
Benchmarks & progress · Government & policy
Trump administration asks OpenAI to limit release of its next model
Officials compared the new model family's capability to Anthropic's Mythos 5; OpenAI limited access to roughly 20 vetted partners before a wider release about twelve days later.
Security & misuse · Government & policy
Commerce Department orders Anthropic to take Fable 5 and Mythos 5 offline worldwide
Amazon researchers had reported a technique bypassing Fable 5's safeguards; Anthropic disputed the order's rationale and said less capable models showed the same weakness.
Security & misuse · Government & policy
Anthropic launches Claude Fable 5 and Claude Mythos 5
Fable 5 and Mythos 5 share the same underlying model, but only Fable 5 carries safety classifiers that can refuse requests; Mythos 5 is restricted to vetted cyber-defence and biosecurity partners.
Models & capabilities · Safety & alignment