Updated

An intricate tower of stacked hand-torn ivory paper leaves and thin terracotta clay shards on a dark background, abstract hero artwork for Claude Fable 5.1

Anthropic

Claude Fable 5.1

Anthropic's Fable 5.1, the same model as Mythos 5.1, for long agentic coding and research.

Chat with Claude Fable 5.1 in Super AgentView pricing

What is Claude Fable 5.1?

Claude Fable 5.1 is Anthropic's model for demanding reasoning and long-horizon agent work, released on September 1, 2026 alongside Claude Mythos 5.1.

Anthropic says it is the same model as Mythos 5.1 with different safeguards, and that it beats Fable 5 at long-running agentic coding, multistep research and document, spreadsheet and slide work. Anthropic also says it goes after root causes and avoids shortcuts, and that at low or medium effort it matches or beats Fable 5 at much lower cost. Thinking is always on, and Super Agent starts it at medium effort.

Provider
Anthropic
Context window
1M tokens
Input
Text, Image
Reasoning
Low to max
Max output
128K tokens
Knowledge cutoff
June 2026
Released
Sep 1, 2026

How Claude Fable 5.1 performs

Published by Anthropic

Results Anthropic reported for Claude Fable 5.1. Each lab runs its own setup, so compare these with other models only inside the same table.

Benchmark results Anthropic published for Claude Fable 5.1
BenchmarkScoreSetting
Terminal-Bench 4.055.8%
Terminal-Bench-Science 0.152.6%
OSWorld 2.077.9%partial
OSWorld 2.041.7%strict
Humanity's Last Exam60.9%no tools
Humanity's Last Exam65.0%with tools
AutomationBench31.4%
CursorBench 3.2.073.4%

Source: anthropic.com

What you can do with Claude Fable 5.1

  • Same model as Claude Mythos 5.1, with different safeguards

  • Stronger than Fable 5 at long agentic coding and multistep research

  • Matches or beats Fable 5 at low or medium effort, per Anthropic

  • Goes after root causes when debugging

  • 1M-token context window with image input

How to prompt Claude Fable 5.1

  • Give it a long, multi-part goal and let it run; that is the work Fable 5.1 is built for.
  • Try low or medium effort first. Anthropic says it matches Fable 5 there at much lower cost.
  • When something breaks, ask for the root cause before the fix.

Where Claude Fable 5.1 fits best

  • Long autonomous projects

  • Multistep research that ends in a written report

  • Debugging a problem that keeps coming back

  • Documents, spreadsheets and slides

How Claude Fable 5.1 compares

Claude Fable 5.1 compared with other chat models on Flashloop
ModelLMArena textLMArena codingContext windowReasoning
Claude Fable 5.11503#51538#131M tokensLow to max
Claude Fable 51503#41551#21M tokensLow to max
Claude Opus 5.51509#21548#41M tokensLow to max
Claude Opus 51491#131528#231M tokensOff to max
Gemini 3.7 Flash1490#161520#361M tokensLow, medium, high

Good to know before you start

  • Always reasons first; there is no thinking-off mode
  • Anthropic's docs suggest Opus 5.5 for most work and Fable 5.1 when Opus falls short
  • Text output only; rendered images and video come from Flashloop's generation models

Start chatting with Claude Fable 5.1

Chat with Claude Fable 5.1 in Super Agent

  1. Select Claude Fable 5.1

    Open Super Agent on Flashloop and choose Claude Fable 5.1 in the model picker.

  2. Enter your prompt

    Ask for what you need: an answer, a plan, or the images and videos you want the agent to make.

  3. Send and keep going

    Send the message. Claude Fable 5.1 answers in Super Agent and runs any generations you asked for.

Questions about Claude Fable 5.1

What improved in Claude Fable 5.1?

Anthropic says Fable 5.1 is stronger than Fable 5 at long-running agentic coding, multistep research and document, spreadsheet and slide work, and costs an estimated 25% less for typical workloads.

How does Claude Fable 5.1 relate to Mythos 5.1?

Anthropic released them together and says they are the same model with different safeguards. Fable 5.1 is the one offered in Super Agent.

Claude Fable 5.1 or Claude Opus 5.5?

Anthropic's docs recommend Opus 5.5 for most workloads and Fable 5.1 for cases where Opus 5.5 at higher effort still falls short. Both are in the featured section of the model picker.

Which reasoning levels does Claude Fable 5.1 support?

Low, medium, high, extra high and max. Super Agent starts it at medium.

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