Claude Fable 5.1 API

anthropic/claude-fable-5.1
Claude Fable 5.1 is Anthropic's most capable model for demanding reasoning and long-horizon agentic work.
Context
1M tokens
Input
$13 / 1M tokens
Output
$65 / 1M tokens
Released
Sep 1, 2026

How to use Claude Fable 5.1 API

Install any OpenAI-compatible SDK, point it at api.aimlapi.com/v1, and set the model to anthropic/claude-fable-5.1.
import requests

r = requests.post(
    "https://api.aimlapi.com/v1/chat/completions",
    headers={"Authorization": "Bearer " + AIMLAPI_KEY},
    json={
      "model": "anthropic/claude-fable-5.1",
      "messages": [
        {
          "role": "user",
          "content": "Hello!"
        }
      ]
    },
)
print(r.json())
const r = await fetch("https://api.aimlapi.com/v1/chat/completions", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.AIMLAPI_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "model": "anthropic/claude-fable-5.1",
    "messages": [
      {
        "role": "user",
        "content": "Hello!"
      }
    ]
  }),
});
console.log(await r.json());
curl -X POST https://api.aimlapi.com/v1/chat/completions \
  -H "Authorization: Bearer $AIMLAPI_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"anthropic/claude-fable-5.1","messages":[{"role":"user","content":"Hello!"}]}'

OpenAI-compatible — swap the base URL and it works with your existing SDK.

Claude Fable 5.1 API Pricing

TypePrice
Input
$13 / 1M tokens
Output
$65 / 1M tokens
Cached input
$0.325 / 1M tokens

Claude Fable 5.1 Benchmarks

BenchmarkScoreWhat it measuresSourceRetrieved
Intelligence
53.4
Composite score across standardised reasoning, knowledge and problem-solving evaluations, measured independently by Artificial AnalysisSourceSeptember 12, 2026
Coding
81.6
Composite score across standardised coding evaluations, measured independently by Artificial AnalysisSourceSeptember 12, 2026

Claude Fable 5.1 vs other models

ModelInputOutputContextBest for
$13 / 1M tokens
$65 / 1M tokens
1M tokens
Long-horizon agentic coding and research
$13 / 1M tokens
$65 / 1M tokens
1M tokens
Chat + assistants
$6.5 / 1M tokens
$39 / 1M tokens
1.05M tokens
Reasoning + agents
$2.6 / 1M tokens
$13 / 1M tokens
1M tokens
Balanced coding + agents
$3.9 / 1M tokens
$19.5 / 1M tokens
1M tokens
Long-context, multimodal & agentic workflows
$0.65 / 1M tokens
$3.9 / 1M tokens
1.05M tokens
Reasoning + agents

Frequently asked questions

Claude Fable 5.1 has a 1,000,000 tokens context window and can return up to 128,000 tokens.

Claude Fable 5.1 takes text as input and returns text.

Use anthropic/claude-fable-5.1 as the model id. Requests go to https://api.aimlapi.com/v1/chat/completions.

Claude Fable 5.1 became available on September 1, 2026.

Claude Fable 5.1 is priced at input $13 / 1M tokens, output $65 / 1M tokens, cached input $0.325 / 1M tokens.

Yes, Claude Fable 5.1 can stream responses as they are generated.

Claude Fable 5.1 was built by Anthropic.

It is built for demanding reasoning and long-horizon agentic work, including coding, multistep research, and document tasks.

Start building with Claude Fable 5.1

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