Anthropic Claude Fable 5.1 — what it is, when to use it and what to use instead

Summary

Claude Fable 5.1 is Anthropic's most expensive model, at $10 per million input tokens and $50 per million output tokens with a 1M-token context window and 128K max output. Anthropic aims it at the hardest reasoning and the longest-running agentic jobs, not at everyday work.

Fable sits above Opus in the Claude line. Anthropic's own guidance is to start on Claude Opus 5 for most workloads and to reach for Fable 5.1 when evaluations on Opus 5 at higher effort still fall short. Fable 5.1 was released on 1 September 2026 and succeeds Claude Fable 5 at the same input and output price, with a June 2026 knowledge cutoff and cache reads at a quarter of the Fable 5 rate.

It accepts text and image input and returns text. Adaptive thinking is always on and cannot be disabled; effort defaults to high, and Anthropic rates its latency as the slowest in the current line-up. Three changes break code written for Fable 5: forced tool use returns an error, earlier models cannot read its thinking blocks, and editing earlier turns invalidates those blocks.

No deprecation has been announced. Anthropic commits to keeping Claude Fable 5.1 available until at least 1 September 2027.

Modality

• Text
• Vision

Use case

• Chat
• Coding
• Reasoning
• Agents & tool use
• Long context

Tier

• Frontier

Access

• Hosted API

Languages

• Multilingual

Specifications

Input price

$10.00 / M tokens

Output price

$50.00 / M tokens

Price band

Flagship

Context window

1M tokens

Max output

128K tokens

Input

Text, image

Output

Text

Knowledge cutoff

June 2026

Tool use

Yes

Structured output

Yes

Weights licence

not published

Model maker

Anthropic

“unknown” means the figure has not been published, or we have not verified it yet — never that the answer is no. “not published” under the weights licence means this model is not offered with downloadable weights. The price band is ours: it bands the blended price (three parts input to one part output) as budget (≤ $0.50), standard (≤ $3), premium (≤ $12) or flagship.

Lifecycle

Anthropic has not announced a deprecation or shutdown date for this model. That is a statement about what has been published, not a guarantee — providers typically announce a shutdown months ahead, and this page updates when they do.

1. Released 1 September 2026
2. Deprecated not announced
3. Retired not announced

Use it for

• Run long-horizon agentic tasks that have to hold a plan across many tool calls without losing the thread.
• Take on reasoning work where Claude Opus 5 at high effort still fails your evaluations.
• Process very large inputs in one pass, using the 1M-token context window and cache reads at $0.25 per million tokens.
• Move off Claude Fable 5, which costs the same per token but has an older knowledge cutoff and four times the cache read price.

Avoid it when

• Cost per call is a constraint; at $10 / $50 this is five times the input price of Claude Sonnet 5 and ten times that of Claude Haiku 4.5.
• You need a fast response per turn; thinking is always on and Anthropic rates its latency as the slowest of the current models.
• Your integration relies on forced tool use, which returns an error on this model.
• Your input includes audio or video; Claude Fable 5.1 accepts text and images only.

Alternatives to consider

• Claude Opus 5 Curated

  Anthropic ● Active

  Half the price at $5 / $25 with the same 1M-token window, and the model Anthropic names as the starting point for most workloads.

  $5.00 in · $25.00 out / M tokens · 1M context

• Claude Fable 5 Curated

  Anthropic ● Active

  The previous Fable release at the same $10 / $50, worth keeping only if you depend on behaviour that changed in 5.1.

  $10.00 in · $50.00 out / M tokens · 1M context

• GPT-6 Astra Curated

  OpenAI ● Active

  OpenAI's top tier at the same $10 / $50, with a 1.05M-token context window and an April 2026 knowledge cutoff.

  $10.00 in · $50.00 out / M tokens · 1.1M context

• Gemini 3.1 Pro Preview Curated

  Google (Gemini) ● Active

  Google's Pro-series preview at $2 / $12, a fifth of the input price, if you are willing to run on a preview model.

  $2.00 in · $12.00 out / M tokens · 1M context

• Claude Fable 5 Derived

  Amazon Bedrock ● Active

  Alternative from Amazon Bedrock, same tier (frontier), similar price; shares chat, coding, reasoning, agents and long-context.

  $10.00 in · $50.00 out / M tokens · 1M context

Curated suggestions were picked by a reviewer, with the reason written by hand. Derived suggestions are ranked from the data — shared tags, the same tier and a comparable price band — not from benchmark scores. Check the capability fit yourself: we track lifecycle, price and specifications.

Sources

• platform.claude.com ↗ https://platform.claude.com/docs/en/models/fable-5-1/overview
• platform.claude.com ↗ https://platform.claude.com/docs/en/about-claude/models/overview
• platform.claude.com ↗ https://platform.claude.com/docs/en/about-claude/pricing
• platform.claude.com ↗ https://platform.claude.com/docs/en/about-claude/model-deprecations

Verified against the source on 10 September 2026. Dataset snapshot 10 September 2026. Providers can change a date without notice — the link above is always the final word.

About this profile

The specifications and dates above are facts from Anthropic, with the sources listed. The summary, the use-for and avoid-when lists and the curated alternatives are our assessment: editorial profile reviewed on 21 September 2026 by llm-researcher.