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SI Model · Anthropic

Claude Fable 5.1

Published Verified 1 min read
On this page
  1. Key specs
  2. Where it fits in the Claude family
  3. Competitors
Claude Fable 5.1 specifications
Developer Anthropic
Released September 1, 2026
Status Current
Inputs Text, Images
Context window 1M tokens
API price (input) $10 / 1M tokens
API price (output) $50 / 1M tokens
Open weights No
Access Claude apps, Claude API, Amazon Bedrock, Google Cloud, Microsoft Foundry

Specs and list prices last verified October 7, 2026. Prices change often; check the provider before you buy.

Strengths

  • Anthropic's top tier for hard reasoning
  • Long-horizon agentic work
  • 1M-token context and 128K output
  • Adaptive thinking always on

Best for

  • Tasks where Claude Opus 5.5 falls short
  • Complex research and analysis
  • Long-running autonomous coding and agent workflows

Claude Fable 5.1 sits at the top of Anthropic’s lineup. Launched on September 1, 2026, it is designed for “demanding reasoning and long-horizon agentic work”. These are tasks that run for hours, span many tools and need the model to plan and self-correct.

Key specs

  • Context window: 1 million tokens; up to 128,000 output tokens
  • Thinking: adaptive and always on, with “high” default effort
  • Price: $10 per million input tokens, $50 per million output; prompt-cache reads cost 2.5% of the input price; batch requests are 50% off
  • Knowledge cutoff: June 2026
  • Availability: Claude apps, Claude API, Amazon Bedrock, Google Cloud and Microsoft Foundry

Where it fits in the Claude family

ModelPrice (in / out per 1M)Anthropic’s description
Claude Fable 5.1$10 / $50Demanding reasoning and long-horizon agentic work
Claude Opus 5.5$4 / $20Long-running agentic coding and knowledge work
Claude Sonnet 5.5$2 / $10Best combination of speed and intelligence

Competitors

Fable 5.1’s direct rival is OpenAI’s GPT-6 Astra, at the same list price. See GPT-6 Astra vs Claude Fable 5.1.

Frequently asked questions

Should I use Claude Fable 5.1 or Claude Opus 5.5?

Anthropic recommends starting with Opus 5.5 for most workloads and using Fable 5.1 for demanding reasoning and long-horizon agentic work, or when Opus 5.5 at higher effort still falls short. Fable costs 2.5× as much.

Sources

  1. Claude models overview — Anthropic

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Compare

Claude Fable 5.1 vs GPT-6 Astra

Specs, pricing and differences.

Model

Claude Opus 5.5

Claude Opus 5.5 is Anthropic's recommended default model, launched September 22, 2026, for long-running agentic coding and knowledge work, at $4/$20 per million tokens.

Model

Claude Sonnet 5.5

Claude Sonnet 5.5 is Anthropic's fast, mid-priced model, launched September 28, 2026, offering what Anthropic calls the best combination of speed and intelligence.