Claude Fable 5.1

Text & chatNewAvailable
by AnthropicModel ID: claude-fable-5-1

Anthropic's model for the most demanding reasoning and long-horizon agentic work. 1M-token context window, up to 128K output tokens, adaptive thinking that is always on.

Price ยท 1M in / out
US$12.00 / US$60.00
Context
1.000.000 tokens
Max. output
128.000 tokens
Input โ†’ output
Text + Image โ†’ Text
Developer
Anthropic
Updated
September 23, 2026
01

Playground

Try Claude Fable 5.1

Chat

US$12.00/1M in
Try Claude Fable 5.1

Send a message. The answer arrives in full once the model is done (no streaming).

System prompt
Max. answer length (tokens)

This run

at most US$0.0615 ยท 6.15 credits reserved

Billed by the tokens actually used; the unused part of the reservation is refunded.

For accounts without a purchase: runs above 2 credits need a top-up.

New here?

5 free credits (US$0.05) when you sign up with Google

Usable 24 hours after sign-up, up to 5 runs per day and at most 2 credits per run. Other sign-in methods start without credits.

02

About Claude Fable 5.1

TL;DRAs of September 23, 2026

Claude Fable 5.1 is a model by Anthropic in the Text & chat category. On Railwail, Claude Fable 5.1 costs US$12.00 per 1M input tokens and US$60.00 per 1M output tokens. The context window holds 1.000.000 tokens, and one response can be up to 128.000 tokens long.

Claude Fable 5.1 is the model Anthropic recommends for demanding reasoning and long-horizon agentic work, or when Claude Opus 5.5 at higher effort still falls short. It accepts text and image input, has a 1M-token context window and returns up to 128K output tokens. Thinking is always on and adaptive, with high as the default effort; sampling parameters such as temperature are not accepted. Anthropic lists its latency as slower than the rest of the current lineup. Reliable knowledge cutoff: June 2026.
03

Pricing

Prices in US dollars. Usage is charged from prepaid credits.
InputUS$12.00 / 1M tokens
OutputUS$60.00 / 1M tokens
  • Billed by the tokens each request actually uses.
  • 1 credit = US$0.01

Cost calculator

Price calculator

/ req.
/ req.

Total

US$4.20

420 credits

Per request

US$0.042 ยท 4.2 credits

Each request is rounded up to 0.01 credits.

04

API

Call Claude Fable 5.1 with your Railwail API key. Use this model ID in the request:
curl https://railwail.com/api/v1/chat/completions \
  -H "Authorization: Bearer $RAILWAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-fable-5-1",
    "messages": [
      {
        "role": "user",
        "content": "Explain what a vector database is in two sentences."
      }
    ],
    "max_tokens": 1024
  }'
Set your key as RAILWAIL_API_KEYCreate API key
05

Specifications

Model ID
claude-fable-5-1
Developer
Anthropic
Category
Text & chat
Input
Text, Image
Output
Text
Context window
1.000.000 tokens
Max. output
128.000 tokens
Billing
By usage (tokens or GPU time)
Released
September 1, 2026
Lifecycle
Current version
Catalog entry updated
September 23, 2026

Input parameters

Inputs and settings from the model's input schema. The example in the API section shows which of them the API accepts.

  • promptrequired

    User message

    Type: Text
    Default: โ€“
    Allowed values: up to 32.000 characters
  • stream
    Type: Yes/no
    Default: false
    Allowed values: โ€“
  • max_tokens
    Type: Integer
    Default: 4096
    Allowed values: 1 to 128.000
  • system_prompt

    Optional system instruction

    Type: Text
    Default: โ€“
    Allowed values: up to 8.000 characters

Tags

  • anthropic
  • claude
  • fable
  • flagship
  • reasoning
  • agentic
  • vision
  • long-context
  • 1m-context
06

Use cases

07

Frequently asked questions

What is Claude Fable 5.1?

Claude Fable 5.1 is a model by Anthropic in the Text & chat category. On Railwail you can call it with an API key through the Railwail API.

How much does Claude Fable 5.1 cost on Railwail?

On Railwail, Claude Fable 5.1 costs US$12.00 per 1M input tokens and US$60.00 per 1M output tokens. You are charged for what each request actually uses. Usage is paid from prepaid credits; 1 credit equals US$0.01.

What is the context window of Claude Fable 5.1?

The context window of Claude Fable 5.1 holds 1.000.000 tokens. One response can be up to 128.000 tokens long.

How fast is Claude Fable 5.1?

There are not enough measured runs of Claude Fable 5.1 on Railwail yet to state a run time. It depends on the input, the settings and the load at the provider.

Is Claude Fable 5.1 better than Claude Opus 5.5?

That depends on the task. Claude Fable 5.1 (Anthropic) and Claude Opus 5.5 (Anthropic) are both models in the Text & chat category. The comparison page shows their prices and specifications side by side.

Compare Claude Fable 5.1 and Claude Opus 5.5

Can Claude Fable 5.1 process images?

Yes. Claude Fable 5.1 accepts images as input in addition to text.

How do I use Claude Fable 5.1 through the API?

Create a Railwail API key and send your request with the model ID claude-fable-5-1. Code examples for curl, Python and JavaScript are in the API section of this page.

08

Comparable models

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Use Claude Fable 5.1 via the API

One API key for every model on Railwail. Usage is charged from prepaid credits, 1 credit = US$0.01.