Claude Fable 5.1 now available in Model ML

Claude Fable 5.1 is now live in Model ML.

Ahead of its launch, we tested Fable 5.1 against the Model ML Composite, the leading benchmark for AI in financial services.

Here’s what stood out to our evals team:

• Fable 5.1 displays best-in-class financial reasoning: Anthropic’s latest model leads on financial workflows and is narrowly ahead of Opus 5 and GPT-5.6 Sol on analytical finance.

• It’s better at holding context: The clearest gain over Fable 5 is carrying financial context through a multi-step analysis, from connecting the reasoning, to keeping assumptions consistent and evidencing conclusions.

Gemini 3.7 Flash remains ahead of Fable 5.1 on multi-document work, and GPT-5.6 Sol leads on complex Excel model construction.

On cost, Fable 5.1 is significantly cheaper than Fable 5 for comparable or better performance, but continues to sit at the top end of the cost range for most tasks.

Fable 5.1 watermarks its text outputs in line with EU AI Act transparency requirements. This will not have any practical impact on the quality or content of Claude’s outputs. Other major model developers have signed the same Code of Practice and will be implementing their own watermarks.

As with Fable 5, Anthropic's safety architecture requires 30-day data retention on all Fable 5.1 traffic, so depending on your setup we'll work with your compliance team to determine whether we can switch on access.

Try Claude Fable 5.1 in Model ML today.