Claude Fable 5.1
Language modelCard summarizedFor demanding reasoning and long-horizon agentic work
Active (latest) · retires not before 1 Sep 2027● Re-checked 12 Oct 2026 · 96 facts · 0 corrections · 1 unconfirmedSource: System Card: Claude Fable 5.1 & Claude Mythos 5.1 (212 pp)
Use it via API
Where to call it
- Claude API
claude-fable-5-1 - Amazon Bedrock
anthropic.claude-fable-5-1 - Google Vertex AI
claude-fable-5-1 - Microsoft Foundry / Azure
claude-fable-5-1
Supports
- Image input
- PDF input
- Structured outputs
- Reasoning control
- Tool calling
- Web search
- Prompt caching
- Batch API
Good for
- Coding, knowledge work and problem-solving, including novel mathematical and scientific reasoning
- Largest gains over Fable 5 in terminal-based scientific and engineering work, computer use, and long-horizon agentic and professional work
- Matches or exceeds Fable 5 at roughly half the cost per task on agentic coding benchmarks
Overview
Fable 5.1
For demanding reasoning and long-horizon agentic work
- Cost
- $10.00 in
- Context
- 1M
- Input / output
- $10.00 / $50.00
- Max output
- 128K
- Knows up to
- June 2026
- Released
- 1 Sep 2026
The general-access configuration of Anthropic's latest and most capable large language model. It shares weights with Claude Mythos 5.1 but adds safeguards that block certain tasks in high-risk dual-use domains such as biology and cybersecurity. It advances coding, knowledge work and problem-solving, with improved novel mathematical and scientific reasoning. p.2
claude-fable-5-1- Input / output per 1M
- $10.00 / $50.00
- Context window
- 1M
- Max output
- 128K
- Knows up to
- June 2026
- Reasoning
- Adaptive (always on)
- Weights
- Closed
About this card. A model card is the maker's own account of a model: what it's for, how it was trained and tested, and where it falls short. This page condenses Anthropic's System Card: Claude Fable 5.1 & Claude Mythos 5.1. Every claim carries its source page.