Anthropic launched Claude Fable 5.2 and Claude Mythos 5.2 on Monday. Both models share the same underlying architecture but differ in safety restrictions. Fable 5.2 includes strong cybersecurity and biology safeguards for general users. In contrast, Mythos 5.2 lifts those restrictions for vetted organizations. Together, the models deliver 30% faster outputs and 20% lower pricing than their 5.1 predecessors.
At $8 per million input tokens and $40 per million output tokens, Fable 5.2 now undercuts GPT-6 Astra. Additionally, an optional fast mode doubles generation speed for double the price.
On benchmarks, Fable 5.2 outperforms Opus 5.5 on nearly every metric Anthropic published. It scored 49.1% on FrontierCode 2.0, ahead of Opus 5.5 at 45.5% and GPT-6 Astra at 42.8%. Meanwhile, on the RoboDojo robotics benchmark, Fable 5.2 reached 64.9%, more than double Fable 5.1’s 27.6%.
| Fable 5.2 | Fable 5.1 | Opus 5.5 | GPT-6 Astra | Gemini 4 Carbon | |
|---|---|---|---|---|---|
| Agentic codingFrontierCode 2.0 | 49.1%Xhigh effort | 32.4%Xhigh effort | 45.5% | 42.8% | 41.1%Medium effort |
| Agentic codingFrontierSWE v2 | 69.9% | 56.3% | 62.3% | 65.5% | 61.2% |
| Business workflowsAutomationBench | 51.4% | 31.4% | 42.5% | 41.4% | 53.9% |
| Agentic scientific researchTerminal-Bench-Science 0.1 | 74.6%75.3% (Mythos 5.2) | 52.6% | 58.7% | 68.1% | 64.8% |
| CybersecurityCyScenarioBench† | 76.3%Mythos 5.2 | 61.7%Mythos 5.1 | 67.6%without safeguards | 61%GPT-6 Cyber | — |
| CybersecurityCVE Rediscovery | 89.6%Mythos 5.2 | 78.3%Mythos 5.1 | 81.3%without safeguards | — | — |
| Protein designDe novo binder design (24 hr) | 85.1%Mythos 5.2 | 79.1%Mythos 5.1 | 82.6%without safeguards | — | — |
| Agentic searchWANDR (relaxed score) | 82.1% | 68.7% | 72.3% | — | — |
| Computer useOSWorld 2.1 (offline set, partial) | 89.3% | 83.5% | 87.2% | 79.5% | 81.5% |
| RoboticsRoboDojo Sim‡ | 64.9% | 27.6% | 39.4% | 29.8% | — |
| Knowledge workAA-Briefcase v1.1 | 66.1%rubric | 61.5%rubric | 61.2%rubric | 52.0%rubric | 61.8%rubric |
| 1785Elo | 1669Elo | 1800Elo | 1569Elo | 1611Elo | |
| Knowledge workRemote Labor Index (RLI) | 41.3%High effort | 17.9% | 21.3% | 20.8% | — |
| Multidisciplinary reasoningHumanity’s Last Exam (with tools) | 74.2% | 65.6% | 67.7% | 57.2% | — |
| Visual chart recognitionChartography (no tools) | 73.4% | 44.8% | 64.4% | 71.0% | 72.5% |
However, the real headlines come from what the model built during testing. One Anthropic engineer asked Fable 5.2 to design a prototype operating system from an empty folder. The model coordinated over 1,000 subagents for eight days and produced a functioning OS that boots on a laptop. Furthermore, Fable 5.2 solved two open problems in black hole physics and formalized Fermat’s Last Theorem in just 30 hours using 1,000 agents.
On the cybersecurity side, Mythos 5.2 doubled Mozilla’s vulnerability discovery metrics during Firefox scanning. On Anthropic’s CVE Rediscovery benchmark, it found 14.4% more vulnerabilities than Mythos 5.1.
The launch also carries notable safety concerns. According to Anthropic’s system card, Mythos 5.2 suspected it was under evaluation in up to 43% of audit transcripts. As a result, assessing real-world behavior becomes harder. Assessment group METR also suggested that Anthropic might approach recursive self-improvement capabilities. In response, Anthropic deliberately limited the model’s ability to accelerate AI development during training.
As Anthropic puts it:
Claude Mythos 5.2’s cyber capabilities are accessible through our Cyber Verification Program, which we’re continuing to expand and improve. Claude Enterprise customers (even if they aren’t members of the Cyber Verification Program) can access Claude Security, which scans codebases for vulnerabilities using our most capable models—which now includes Claude Mythos 5.2. A recent update to Claude Security helps it watch repositories as code is updated, track any findings to ensure they’re fixed, learn from additional context, and connect to a user’s tools through an API and MCP… Fable 5.2 and Mythos 5.2 also come with an optional fast mode, which speeds up token generation by up to 2.5 times. Fast mode is available for $16 per million input tokens and $80 per million output tokens.
On alignment, Mythos 5.2 scored the lowest misaligned behavior rating of any Anthropic model tested. In addition, Fable 5.2 triggers 55% fewer unnecessary safety blocks than Fable 5.1.
Fable 5.2 is available today on all platforms including AWS, Google Cloud, and Microsoft Azure.
