Technical Specifications of Claude Mythos 5
| Item | Specification |
|---|---|
| Model Name | Claude Mythos 5 |
| Provider | Anthropic |
| API Model ID | claude-mythos-5 |
| Model Class | Mythos-class (restricted-access flagship) |
| Input Types | Text, Images |
| Output Types | Text |
| Context Window | 1,000,000 tokens |
| Maximum Output Tokens | 128,000 tokens |
| Reasoning Mode | Adaptive Thinking (always enabled) |
| Core Strengths | Long-horizon reasoning, autonomous agents, advanced software engineering, cybersecurity research, scientific discovery |
| Availability | Limited access via Project Glasswing |
| Safety Profile | Shares Fable 5 architecture but without Fable's additional safety classifiers |
| Predecessor | Claude Mythos Preview |
Specifications are based on Anthropic's official documentation and launch materials.
What Is Claude Mythos 5?
Claude Mythos 5 is Anthropic's most advanced frontier AI model and the unrestricted counterpart to Claude Fable 5. Both models share the same underlying architecture, but Mythos 5 is offered without the extra safety classifiers that Fable 5 uses to screen or redirect certain high-risk requests.
Rather than being generally available through the Claude API, Mythos 5 is currently limited to approved organizations participating in Project Glasswing, including selected cybersecurity defenders, critical infrastructure operators, and research institutions. Anthropic has stated that access will gradually expand through a broader trusted-access program.
Main Features of Claude Mythos 5
- 1 million token context window, allowing repository-scale code analysis and extremely large document workflows.
- Adaptive Thinking architecture, where reasoning is always active and can be tuned using the
effortparameter. - Long-duration autonomous operation, enabling agents to work on complex tasks for hours or days with minimal intervention.
- Advanced software engineering, including multi-file refactoring, code migration, debugging, and evaluation harness generation.
- Strong multimodal capabilities, supporting image understanding alongside text-based reasoning.
- Higher-trust cybersecurity and scientific workflows, made possible by removing the additional safety classifiers present in Claude Fable 5.
Benchmark Performance of Claude Mythos 5
Anthropic has not published a separate benchmark table for Claude Mythos 5 because it is effectively the same underlying model as Claude Fable 5. The company instead emphasizes that the Mythos architecture is "state of the art on nearly all tested benchmarks" and excels in:
- Repository-scale software engineering.
- Long-horizon autonomous agent tasks.
- Scientific research and technical analysis.
- Vision and multimodal reasoning.
- Complex cybersecurity and critical infrastructure workflows.
According to Anthropic, the advantage of the Mythos architecture becomes larger as tasks become longer and require sustained planning or iterative tool use.
Claude Mythos 5 vs Claude Fable 5 vs Claude Opus 4.8
| Feature | Claude Mythos 5 | Claude Fable 5 | Claude Opus 4.8 |
|---|---|---|---|
| Public Availability | Limited | General availability | General availability |
| Context Window | 1M tokens | 1M tokens | Large context |
| Adaptive Thinking | Always enabled | Always enabled | Standard reasoning modes |
| Long-Horizon Agent Work | Excellent | Excellent | Strong |
| Safety Classifiers | Minimal / trusted-access model | Additional safeguards enabled | Standard safeguards |
| High-Risk Cyber/Bio Requests | Available to approved partners | May trigger fallback | Supported under standard policies |
| Target Users | Cyber defenders, research organizations, critical infrastructure | Enterprises and developers | General-purpose professional users |
Limitations
- Claude Mythos 5 is not generally available and requires approval through Project Glasswing.
- Anthropic currently restricts access to trusted organizations because of the model's advanced cybersecurity and scientific capabilities.
- Unlike Claude Fable 5, Mythos 5 is not intended for broad consumer deployment at this stage.
Representative Use Cases
- Critical infrastructure security analysis.
- Repository-scale software engineering and automated code migration.
- Long-running AI agents for research and enterprise workflows.
- Scientific literature synthesis and hypothesis generation.
- Advanced cybersecurity defense and vulnerability analysis.
- Large-scale legal, financial, and technical document processing.