Can Claude Fable 5 handle million-token documents through the API?

Yes. Claude Fable 5 supports a 1,000,000-token context window.

When should I use Claude Fable 5 instead of Claude Opus 4.8?

Use Claude Fable 5 for advanced reasoning, large-context analysis, and agent workflows.

How does Claude Fable 5 compare with Claude Mythos 5?

Fable 5 includes safety classifiers while Mythos 5 has broader capabilities and restricted access.

Is Claude Fable 5 suitable for autonomous coding agents?

Yes. It is optimized for long-running software engineering and agentic workflows.

Does Claude Fable 5 support image inputs?

Yes. It supports vision-based reasoning with screenshots, diagrams, and visual documents.

What are the main limitations of the Claude Fable 5 API?

Some cybersecurity, biology, chemistry, and distillation requests are restricted.

Can Claude Fable 5 be used for scientific research workflows?

Yes. It performs strongly on research, analysis, and scientific reasoning tasks.

Why is Claude Fable 5 considered a Mythos-class model?

It belongs to Anthropic's newest frontier architecture focused on advanced reasoning and long-horizon task execution.

Affordable Claude Fable 5 API | text-to-text

Playground for Claude Fable 5

Explore Claude Fable 5's Playground — an interactive environment to test models, run queries in real time. Try prompts, adjust parameters, and iterate instantly to accelerate development and validate use cases.

Technical Specifications of Claude Fable 5

Item	Specification
Model Name	Claude Fable 5
Provider	Anthropic
API Model ID	claude-fable-5
Model Class	Mythos-class (public safeguarded version)
Input Types	Text, Images
Output Types	Text
Context Window	1,000,000 tokens
Maximum Output Tokens	Up to 128,000 tokens
Core Strengths	Long-horizon reasoning, agentic workflows, coding, scientific research, vision
Availability	Anthropic API, Claude apps, Amazon Bedrock, major cloud partners
Safety Architecture	Automatic fallback to Claude Opus 4.8 for certain high-risk domains
Companion Model	Claude Mythos 5 (restricted-access variant)

Technical specifications are based on Anthropic's official model documentation and launch materials.

What Is Claude Fable 5?

Claude Fable 5 is Anthropic's most capable generally available AI model and the first public release built on its new Mythos-class architecture. It is designed for demanding reasoning tasks, autonomous multi-step workflows, large-scale software engineering, scientific research assistance, and extended agentic operations.

Fable 5 shares its underlying architecture with the restricted-access Claude Mythos 5, but includes additional safety classifiers. If requests enter certain high-risk domains—such as offensive cybersecurity, hazardous biology, chemistry, or model distillation—the system automatically routes the interaction to the safer Claude Opus 4.8 model. Anthropic states these safeguards activate in fewer than 5% of average sessions.

Key Features of Claude Fable 5 API

Claude Fable 5 shines in scenarios where previous models falter on complexity or duration.

1. Long-Horizon Autonomy and Agentic Workflows

Fable 5 maintains coherence across multi-stage tasks, planning, delegating to sub-agents, tracking dependencies, and self-verifying. It outperforms priors in sustained agentic coding and computer-use benchmarks like OSWorld-Verified (85.0%).

Developers report it handling day-long codebase migrations in massive repos with minimal intervention.

2. Superior Coding and Software Engineering

Headline strength: State-of-the-art on agentic coding evals. It understands project context, reasons through dependencies, generates production-grade code, debugs, refactors, and tests iteratively.

Claude Fable 5

3. Multimodal Vision and Document Reasoning

Excels at interpreting diagrams, charts, screenshots, scientific figures, and PDFs. Leads on GDP.pdf (29.8%) and spatial reasoning benchmarks.

4. Large-Context Knowledge Work

Handles massive inputs (codebases, research corpora, financial docs) while preserving nuance. Strong on knowledge work evals like GDPval-AA.

5. Enhanced Safety and Reliability

Safety is central to Fable 5's design. As a "safe for general use" version of the more powerful Mythos 5, it incorporates classifier-based safeguards that detect and reroute sensitive queries—particularly those involving cybersecurity, biology, chemistry, or model distillation—to Claude Opus 4.8 or equivalent safer behaviors.

This hybrid approach allows Fable 5 to deliver Mythos-level intelligence for most tasks while mitigating risks. False positive rates are low (~5% in some reports), ensuring minimal disruption for legitimate use.

Claude Fable 5

Benchmark Performance of Claude Fable 5

Anthropic describes Claude Fable 5 as "state of the art on nearly all tested benchmarks" and reports that its advantage becomes more pronounced as tasks grow longer and more complex. Public launch materials highlight exceptional performance in:

Software engineering and large codebase reasoning.
Autonomous knowledge work and document analysis.
Scientific research and technical problem solving.
Vision and multimodal understanding.
Long-running agent workflows requiring sustained planning.

While Anthropic has not publicly released a full benchmark table for every evaluation suite, it positions Fable 5 above previous Claude generations, including Claude Opus 4.8, particularly for long-duration autonomous tasks.

Claude Fable 5 vs Claude Opus 4.8 vs Claude Mythos 5

Feature	Claude Fable 5	Claude Opus 4.8	Claude Mythos 5
Public Availability	Yes	Yes	Limited access
Context Window	1M tokens	Large context	1M tokens
Long-Horizon Agent Work	Excellent	Strong	Excellent
Software Engineering	State-of-the-art	Advanced	State-of-the-art
Safety Guardrails	Yes	Standard	Reduced
High-Risk Cyber/Bio Tasks	Falls back to Opus 4.8	Supported within standard policies	Greater capability for trusted partners
Primary Audience	General developers & enterprises	General-purpose AI users	Approved cybersecurity and research organizations

Limitations

Some cybersecurity, biology, chemistry, and model-distillation requests are automatically redirected to Claude Opus 4.8.
The conservative safeguard system can occasionally trigger on benign requests.
Access to the unrestricted Mythos-level capabilities remains limited to trusted organizations through Project Glasswing.

Typical Use Cases

Repository-scale software development and code migration.
Enterprise document analysis and knowledge management.
Long-form research and technical writing.
Scientific literature review and hypothesis generation.
AI agents that require persistent multi-step planning.
Legal, financial, and consulting workflows involving very large datasets.

How to Build with Claude Fable 5 API on CometAPI

Step 1: Get Your Claude Fable 5 API Key

Sign up or log in to CometAPI, then generate an API key from your dashboard. Use this key to authenticate Claude Fable 5 API requests from your application or backend service. Before you start building, check the latest API documentation for the current endpoint, model name, and supported parameters.

CometAPI’s playground lets you experiment instantly. For production, leverage their docs for rate limits, streaming, and tool use.

Step 2: Test Claude Fable 5 API with Real Tasks

Use realistic prompts instead of simple test messages. Try tasks such as coding, document analysis, structured data extraction, research summarization, or agent-style planning. During testing, evaluate response quality, instruction following, output formatting, and long-context performance.

Step 3: Integrate Claude Fable 5 API into Your Workflow

After testing, integrate Claude Fable 5 into your target use case, such as coding assistants, document review, research tools, or business automation. Use structured outputs, logging, and human review where needed, especially for important or production-facing workflows.

What Makes CometAPI Practical for Claude Fable 5 API Integration

Multi-Model Flexibility: Experiment with Fable 5 vs. GPT-5.5, Grok, or open-source options in one platform—optimize for cost/performance per task.

Cost Efficiency and Predictability: Credit-based usage, potential discounts, and no surprise vendor bills. Perfect for variable workloads where Fable 5’s higher output pricing benefits from optimization.

Seamless Production Readiness: OpenAI compatibility means drop-in replacement in existing LangChain, LlamaIndex, or custom agents. Robust handling of long contexts and fallbacks.

Support and Ecosystem: 24/7 resources, community, and enterprise features (security, compliance). Continuous addition of new models keeps your stack future-proof.

Real-World Wins: Developers use CometAPI to route Fable 5 for heavy reasoning/coding while using lighter models for simple queries—maximizing ROI.

By choosing CometAPI, teams focus on building innovative applications rather than infrastructure.

FAQ

Pricing for Claude Fable 5

Explore competitive pricing for Claude Fable 5, designed to fit various budgets and usage needs. Our flexible plans ensure you only pay for what you use, making it easy to scale as your requirements grow. Discover how Claude Fable 5 can enhance your projects while keeping costs manageable.

Model	Comet Price (USD / M Tokens)	Official Price (USD / M Tokens)	Discount
claude-fable-5	Input:$8/M Output:$40/M	Input:$10/M Output:$50/M	-20%

Sample code and API for Claude Fable 5

Access comprehensive sample code and API resources for Claude Fable 5 to streamline your integration process. Our detailed documentation provides step-by-step guidance, helping you leverage the full potential of Claude Fable 5 in your projects.

POST

/v1/chat/completions

POST

/v1/messages

# Get your CometAPI key from https://www.cometapi.com/console/token
# Export it as: export COMETAPI_KEY="your-key-here"
curl https://api.cometapi.com/v1/messages \
  --header "Authorization: $COMETAPI_KEY" \
  --header "content-type: application/json" \
  --data \
'{
  "model": "claude-fable-5",
  "max_tokens": 4096,
  "thinking": {
    "type": "adaptive",
    "display": "summarized"
  },
  "output_config": {
    "effort": "medium"
  },
  "messages": [
    {
      "role": "user",
      "content": "Analyze the trade-offs between microservices and monolithic architectures"
    }
  ]
}'

cURL Code Example

# Get your CometAPI key from https://www.cometapi.com/console/token
# Export it as: export COMETAPI_KEY="your-key-here"
curl https://api.cometapi.com/v1/messages \
  --header "Authorization: $COMETAPI_KEY" \
  --header "content-type: application/json" \
  --data \
'{
  "model": "claude-fable-5",
  "max_tokens": 4096,
  "thinking": {
    "type": "adaptive",
    "display": "summarized"
  },
  "output_config": {
    "effort": "medium"
  },
  "messages": [
    {
      "role": "user",
      "content": "Analyze the trade-offs between microservices and monolithic architectures"
    }
  ]
}'

Python Code Example

import os

import anthropic

client = anthropic.Anthropic(
    base_url="https://api.cometapi.com",
    api_key=os.environ["COMETAPI_KEY"],
)

message = client.messages.create(
    model="claude-fable-5",
    max_tokens=4096,
    thinking={"type": "adaptive", "display": "summarized"},
    output_config={"effort": "medium"},
    messages=[
        {
            "role": "user",
            "content": "Analyze the trade-offs between microservices and monolithic architectures",
        }
    ],
)

for block in message.content:
    if block.type == "thinking" and block.thinking:
        print(f"[Thinking]\n{block.thinking}\n")
    elif block.type == "text":
        print(block.text)

JavaScript Code Example

import Anthropic from "@anthropic-ai/sdk";

const anthropic = new Anthropic({
  apiKey: process.env.COMETAPI_KEY,
  baseURL: "https://api.cometapi.com",
});

const message = await anthropic.messages.create({
  model: "claude-fable-5",
  max_tokens: 4096,
  thinking: {
    type: "adaptive",
    display: "summarized",
  },
  output_config: {
    effort: "medium",
  },
  messages: [
    {
      role: "user",
      content: "Analyze the trade-offs between microservices and monolithic architectures",
    },
  ],
});

for (const block of message.content) {
  if (block.type === "thinking" && block.thinking) {
    console.log(`[Thinking]\n${block.thinking}\n`);
  } else if (block.type === "text") {
    console.log(block.text);
  }
}

Uptime

Request success rate over the last 30 days, reflecting the reliability of each model provider. CometAPI monitors all connected providers in real time, 24/7.

RespondLIVE

7635msAvg. Response

UptimeLIVE

100.0%Avg. Uptime

Versions of Claude Fable 5

The reason Claude Fable 5 has multiple snapshots may include potential factors such as variations in output after updates requiring older snapshots for consistency, providing developers a transition period for adaptation and migration, and different snapshots corresponding to global or regional endpoints to optimize user experience. For detailed differences between versions, please refer to the official documentation.

Version
claude-fable-5