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Claude Fable 5.1
Anthropic · Fable
Anthropic released Claude Fable 5.1 on September 1, 2026.
Claude Fable 5.1 is the Anthropic model launched on September 1, 2026 as the successor to Claude Fable 5, for long-running agentic coding, knowledge work and research. It launched alongside Claude Mythos 5.1 for Project Glasswing participants. It supports a 1M token context window by default, 128k max output tokens and always-on adaptive thinking, at $10 / $50 per million input / output tokens, the same as Fable 5, with prompt cache reads cut to $0.25 per million tokens. It is available on the Claude API, Amazon Bedrock, Claude Platform on AWS, Google Cloud and Microsoft Foundry. Like Fable 5 it requires 30-day data retention, and its text output carries Anthropic's text watermark.
Claude Fable 5.1 at a glance
- Released
- API model id
claude-fable-5-1- Available on
- Claude APIAmazon BedrockClaude Platform on AWSGoogle CloudMicrosoft Foundry
- Previous model
- Claude Fable 5 (June 9, 2026)
- Announcement
- platform.claude.com
What changed from Claude Fable 5
Compared with Claude Fable 5, cache reads are much cheaper (0.025x the base input price instead of 0.1x), and the price is otherwise unchanged.
Forced tool use (tool_choice any or tool) now returns an error, so schema-conformant tool inputs should use strict tool use. Thinking blocks are preserved only for the model that produced them or a newer one, and Anthropic added text watermarking and C2PA credentials on generated files.
New to model names and version numbers? Read how AI labs version their models.
Claude Fable 5.1 release timeline
The launch and every later Anthropic release that mentions Claude Fable 5.1, oldest first.
- Claude Fable 5.1 and Mythos 5.1 launch
Launched Claude Fable 5.1 and Claude Mythos 5.1, world's most advanced models for coding and knowledge work.
Source: Claude Help Center Release Notes - Dreams research preview expanded
Dreams (research preview) now supports Claude Opus 5.5, Claude Fable 5.1, and Claude Sonnet 5.5.
Source: Claude Platform Release Notes
Claude Fable 5.1 FAQ
When was Claude Fable 5.1 released?
Anthropic released Claude Fable 5.1 on September 1, 2026. The launch entry below links to the official announcement.
Where is Claude Fable 5.1 available?
Claude Fable 5.1 is available on Claude API, Amazon Bedrock, Claude Platform on AWS, Google Cloud and Microsoft Foundry. Later availability changes are listed under follow-up releases on this page.
What is the Claude Fable 5.1 API model id?
Use claude-fable-5-1 in Anthropic's API.
What came before Claude Fable 5.1?
Claude Fable 5.1 follows Claude Fable 5, released on June 9, 2026.
Other Anthropic models
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