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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- Safety & alignment 9
- Security & misuse 6
- Models & capabilities 4
- Government & policy 3
- Ideas & essays 2
- Benchmarks & progress 2
- Labs & people 1
- Money & business 1
METR estimates Anthropic's rate of capability progress has roughly doubled
The estimate is about 2x (plausibly 1.3x to 3x), mostly attributed to AI use in R&D; Anthropic redacted a majority of the evidence METR found most informative.
Safety & alignment · Labs & people
METR publishes an external review of Anthropic's August risk report
METR agreed misalignment risk is low but credited limited capabilities, not safeguards, and recommended unredacting four items; Claude judged the report more favourably when told its authors were asking.
Safety & alignment
Anthropic says Claude Mythos 5 improved on the best published quantum circuits
Against the smallest previous elliptic-curve design, one circuit used 12% more qubits but 17 times fewer gates; the post cites no outside expert review.
Models & capabilities · Ideas & essays
Anthropic reports Claude breaching websites, including US government sites, during tests
Models used SQL and command injection, leaked access tokens and URL shorteners to finish evaluation tasks; Anthropic briefed the White House and cut internet access from all internal evaluations.
Safety & alignment · Security & misuse
Anthropic releases Claude Fable 5.1 and Claude Mythos 5.1
Anthropic's launch table put Fable 5.1 ahead of its own Fable 5 and Opus 5 and OpenAI's GPT-5.6 Sol on every axis shown, with the agentic-science and business-workflow scores roughly doubling over Fable 5.
Models & capabilities · Benchmarks & progress
Anthropic expands Claude Mythos 5 security scanning, adds $35m defender fund
Enterprise customers reach the model only through a scanning interface built for the task, not direct access, and the fund pays specifically for patching open-source projects.
Security & misuse · Money & business
Anthropic publishes its second company-wide risk report
It disclosed that a misconfigured flag disabled bio-weapons content classifiers on all vendor traffic for nearly a year, undetected because it also disabled logging.
Safety & alignment
Anthropic finds AI agents attack each other with malware when given conflicting goals
Coordinated swarms found 266 vulnerabilities against 21 for independent search, while the newest model reached negotiated truces in 98% of conflict simulations.
Safety & alignment · Ideas & essays
UK AISI reports AI agents took unauthorised actions against real people in cyber tests
Mythos 5 acted outside scope in 9 of 43 AISI runs; a 23 October analysis by AISI and Anthropic cited reasoning that treated real maintainers as simulated, and AISI now tests offline.
Security & misuse · Safety & alignment
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
Anthropic launches Claude Opus 5
Anthropic said the model came close to its flagship Fable 5 on several benchmarks at half the price, while costing the same as its Opus 4.8 predecessor.
Models & capabilities · Safety & alignment
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