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Anthropic · Frontier

Claude Fable 5.1

Added Sep 1, 2026

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Use in the app

Claude Fable 5.1 improves on Fable 5 across agentic coding, long-running workflows, front-end and visual code generation, finance, analysis, and knowledge work, with more concise plans and summaries. Anthropic retains prompts and outputs for 30 days; Zero Data Retention is not available.

  • Reasoning
  • Tools
  • Vision
  • Structured output
  • PDF input
Input
Text, Images
Output
Text
Reasoning effort
low · medium · high · xhigh · max
Discovery tier
Frontier

Pricing

USD per 1M tokens
Input
$10.00
Output
$50.00
Cache read
$0.25
Cache write
$12.50
$20.00 for a 1-hour cache

Reference prices as published by the model provider. API example

Specifications

Context window
1M
Max output
128K
Average output (7 days)
2.3K tokens
Longer than 93% of 465 models

Side by side

Claude Fable 5.1 compared

Specifications, prices, speed and benchmark scores next to each other. Benchmarks below show every compared model too.

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Claude Fable 5.1AnthropicThis modelClaude Haiku 5.5AnthropicRemove
ProviderAnthropicAnthropic
Discovery tierFrontierEfficient
AddedSep 1, 2026Oct 7, 2026
Limits
Context window1M1M
Max output128K128K
Average output2.3K tokens1.5K tokens
Pricing, USD per 1M tokens
Input$10.00$0.10Best
Output$50.00$0.50Best
Cache read$0.25$0.01Best
Cache write$12.50$0.13Best
Performance
Throughput136.6 tok/s276.6 tok/sBest
Time to first token6.4 s3.1 sBest
Request success (24h)98.9%99.9%Best
Benchmark indexes
Intelligence Index53.4Best43.4
Coding Index81.6—
Capabilities
ReasoningYesYes
ToolsYesYes
VisionYesYes
Structured outputYesYes
PDF inputYesYes
Reasoning effortlow, medium, high, xhigh, maxlow, medium, high, xhigh, max

Public evaluations

Benchmarks

Independent evaluation results, with how each score ranks among the models in the Noumen catalog.

  • Claude Fable 5.1
  • Claude Haiku 5.5

Intelligence Index

  • Claude Fable 5.153.4
  • Claude Haiku 5.543.4

Claude Fable 5.1 tested at max reasoning effort

Claude Fable 5.1: Better than 98% of 326 scored models

3.8Catalog models by score55.1

Indexes

  • Coding Index

    Composite of the coding evaluations

    • Claude Fable 5.1: 81.6
    • Claude Haiku 5.5: —

Agentic work

  • AutomationBench-AA

    Workflow automation, penalized for guardrail violations

    • Claude Fable 5.1: 59.4%Top
    • Claude Haiku 5.5: 35.4%

  • AutomationBench-AA tasks completed

    Workflows finished end to end without a guardrail violation

    • Claude Fable 5.1: 32.1%Top
    • Claude Haiku 5.5: 13.9%

  • Harvey LAB-AAv1.1

    Legal tasks passed in full, with no material hallucination

    • Claude Fable 5.1: 6.4%Top
    • Claude Haiku 5.5: 0.6%

  • AA-Briefcasev1.1

    Agentic knowledge work, rated head to head

    • Claude Fable 5.1: 1,671 EloTop
    • Claude Haiku 5.5: 1,575 Elo

  • GDPval-AAv2.1

    Economically valuable occupational tasks, rated head to head

    • Claude Fable 5.1: 1,755 EloTop
    • Claude Haiku 5.5: 1,619 Elo

Document reasoning

  • GDP.pdf

    Professional reasoning over PDF documents, all-pass rate

    • Claude Fable 5.1: 26.2%Top
    • Claude Haiku 5.5: 20.8%

  • AA-LCRv1.1

    Reasoning across long documents

    • Claude Fable 5.1: 85.3%Top
    • Claude Haiku 5.5: 82.7%

  • MLCR-AA

    Long-context reasoning over medical records

    • Claude Fable 5.1: 15.6%
    • Claude Haiku 5.5: 35.0%Top

Reasoning and knowledge

  • Humanity’s Last Exam

    Expert-level questions across academic fields

    • Claude Fable 5.1: 59.1%Top
    • Claude Haiku 5.5: 44.4%

  • GPQA Diamond

    Graduate-level science questions

    • Claude Fable 5.1: 93.7%
    • Claude Haiku 5.5: —

Coding

  • Terminal-Benchv4.0

    Practical software engineering in a terminal

    • Claude Fable 5.1: 52.0%Top
    • Claude Haiku 5.5: 32.8%

  • SciCode

    Scientific computing in Python

    • Claude Fable 5.1: 63.1%Top
    • Claude Haiku 5.5: 55.0%

Legacy evaluations

  • AA-LCR (unversioned)

    Long-context reasoning, earlier grading

    • Claude Fable 5.1: 85.3%Top
    • Claude Haiku 5.5: 82.7%

Scores from Artificial Analysis, updated Oct 26, 2026. Claude Fable 5.1 was tested at max reasoning effort; compare scores measured at the same effort.Artificial Analysis

Live routing data

Performance and reliability

Recent averages across requests routed for this model. Your own speed depends on prompt length, reasoning effort and load.

Throughput
136.6 tok/s
Faster than 71% of 250 models
Time to first token
6.4 s
Quicker than 24% of 250 models
Prompt cache hits
9.8%
About $9.04 per 1M input tokens with caching
Request success (24h)
98.9%
Reliable

Cache hits are the share of input tokens recently served from a prompt cache across all requests. They are not a forecast of your own hit rate.

Hourly request success · last 72 hoursLowest hour 87.8%
  • Healthy (98% or more)
  • Degraded (90–98%)
  • Down (under 90%)
  • No requests

Developers

Use it through the API

Noumen’s API is OpenAI-compatible: any Chat Completions client works with a base URL and a key.

Read the quickstart
curl https://www.noumen.xyz/api/v1/chat/completions \
  -H "Authorization: Bearer $NOUMEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "anthropic/claude-fable-5.1",
    "reasoning_effort": "medium",
    "messages": [{ "role": "user", "content": "Explain this stack trace." }]
  }'
import os
from openai import OpenAI

client = OpenAI(base_url="https://www.noumen.xyz/api/v1", api_key=os.environ["NOUMEN_API_KEY"])
reply = client.chat.completions.create(
    model="anthropic/claude-fable-5.1",
    messages=[{"role": "user", "content": "Explain this stack trace."}],
)
print(reply.choices[0].message.content)

Anthropic

Other Anthropic models, starting with the same family.