Claude Fable 5.1

Claude Fable 5.1 is an Anthropic model released on September 1, 2026, with the API ID claude-fable-5-1.

Lab: Anthropic
Release date: September 1, 2026
Status: Generally available
API model ID: claude-fable-5-1
Context window: 1,000,000 tokens
Max output: 128,000 tokens

Anthropic released Claude Fable 5.1 on September 1, 2026, the date in the Claude Platform release notes, as claude-fable-5-1. Anthropic’s model docs list a 1M-token context window, 128K max output tokens, text and image input with text output, and a June 2026 knowledge cutoff. It is available on the Claude API, Amazon Bedrock, Claude Platform on AWS, Google Cloud and Microsoft Foundry.

It shares its underlying model with Claude Mythos 5.1, which runs with different safeguards and limited access.

Modalities: Text and image input; text output
Knowledge cutoff: June 2026
Availability: Claude API, Amazon Bedrock, Claude Platform on AWS, Google Cloud, Microsoft Foundry.
Official source: anthropic.com
Last checked: October 5, 2026

Questions

When was Claude Fable 5.1 released?

Anthropic released Claude Fable 5.1 on September 1, 2026, the date in the Claude Platform release notes.

What is the context window of Claude Fable 5.1?

Anthropic’s model docs list a 1M-token context window and 128K max output tokens.

Where is Claude Fable 5.1 available?

It is available on the Claude API, Amazon Bedrock, Claude Platform on AWS, Google Cloud and Microsoft Foundry.

How is Claude Fable 5.1 related to Claude Mythos 5.1?

Both share the same underlying model; Claude Mythos 5.1 runs with different safeguards and limited access.

Source

Release dates, model IDs and limits come from each lab’s own announcement, changelog, documentation or deprecations page, linked on every model with the date it was last checked. How we pick and check sources: editorial standards.