Anthropic has announced Claude Fable 5.1 and Claude Mythos 5.1, its most advanced models for coding and knowledge work. The releases also showcase research capabilities that the company says offer an early glimpse of how AI models will contribute to scientific progress.
What’s New in 5.1
The 5.1 updates build on the Fable and Mythos model families introduced earlier this year:
- Claude Fable 5.1 — the flagship for long-running coding agents and complex software engineering work
- Claude Mythos 5.1 — optimized for knowledge work, research, analysis, and professional tasks
Both models deliver improvements in:
- Coding performance — better results on real-world software engineering benchmarks
- Long-horizon agents — improved ability to work on multi-hour tasks with consistent focus
- Research capabilities — early evidence of models contributing meaningfully to scientific questions
The Research Angle
What makes this release notable is Anthropic’s framing around scientific progress. The company says the research capabilities of these models offer “an early glimpse of how AI models will contribute to scientific progress” — a signal that frontier models are moving from tools that assist researchers to systems that can generate novel scientific insight.
This aligns with Anthropic’s recently expanded support for scientists and its work on research-focused deployments like Claude Science.
Positioning in the Model Lineup
With Fable 5.1 and Mythos 5.1, Anthropic’s model lineup now spans:
- Fable — frontier coding and agentic work
- Mythos — knowledge work and research
- Opus — long-running agents and professional work
- Sonnet — balanced performance at scale
- Haiku — fast, lightweight tasks
Availability
Claude Fable 5.1 and Claude Mythos 5.1 are available now through the Claude app, API, and enterprise deployments including AWS and Google Cloud.
The release comes just weeks after Anthropic previewed the Model Hardware Standard and expanded its support for scientists — part of a broader push into research applications and safety standards for physical AI.