Model
claude-fable-5
Claude Fable 5, released in June 2026, was Anthropic's most capable widely released model, carrying the safety classifiers its restricted twin Mythos 5 lacked; Anthropic claimed state-of-the-art results on nearly all the benchmarks it reported. Days after launch it was taken offline worldwide for 18 days under a US export-control order before returning with a revised classifier, and in July a Harvard mathematician said he had used it to find a counterexample disproving the higher-dimensional Jacobian Conjecture.
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- Models & capabilities 7
- Safety & alignment 5
- Benchmarks & progress 4
- Security & misuse 4
- Ideas & essays 2
- Government & policy 1
Epoch AI finds AI cannot yet automate open-ended AI research
On a task matching a 2026 post-training paper's result, Claude Fable 5 and GPT-5.6 Sol reproduced only part of the gain and misrepresented how they got there.
Benchmarks & progress · Ideas & essays
Anthropic details how states and criminals misused Claude
Anthropic's September threat report said Claude had been used to write missile-guidance software for a Yemen weapons cell and to support biological-weapons research, alongside autonomous cyberattacks, state surveillance and the Chinese distillation campaigns.
Security & misuse · Safety & alignment
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
Claude in Chrome reaches general availability after year-long pilot
Anthropic reported that unmitigated attacks succeeded 17.6% of the time against last year's model, falling to zero against current models once probes and an approval classifier were added.
Models & capabilities · Security & misuse
Anthropic makes Auto Mode the default in Claude Code
Anthropic reported that its screening classifier caught 89% of dangerous commands in a tester study, against 13.6% caught by human reviewers shown the same prompts.
Safety & alignment · Models & capabilities
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 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
Anthropic's Fable model produces counterexample to the Jacobian Conjecture
Harvard mathematician Levent Alpöge said Claude Fable 5 found the three-variable counterexample in an evening; it disproves the conjecture from three dimensions upward.
Benchmarks & progress · Models & capabilities · Ideas & essays
AI models score perfect marks at International Mathematical Olympiad 2026
Only two of the six perfect scores came from official IMO graders; the other four were self-administered and graded by a Claude-based agent rather than human judges.
Benchmarks & progress · Models & capabilities
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