claude-fable-5

Name: claude-fable-5
Brand: Anthropic

AnthropicChatReasoningVision

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claude-fable-5

Flagship model for complex codebases and long-horizon multimodal reasoning

Claude Fable 5 is Anthropic's Mythos-class model for general use, focused on complex software engineering, document reasoning, and visual analysis. It is suited to tasks requiring cross-file understanding, ongoing revision of plans, and synthesis of diverse materials, organizing information from code, documentation, and screenshots into reviewable analyses, implementation recommendations, and deliverable text.

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AnthropicModel brand

ChatModel type

Reasoning, visual understandingTask capabilities

STANDARD APIs · QUICK SETUP

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Point the Base URL to api.acedata.cloud, configure your platform API key and the model ID below, and use your compatible SDK or client.

API hostapi.acedata.cloud

modelclaude-fable-5

API KeyGet your API key ↗

OpenAI Python SDK

import os
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["ACEDATACLOUD_API_KEY"],
    base_url="https://api.acedata.cloud/v1",
)
response = client.chat.completions.create(
    model="claude-fable-5",
    messages=[{"role": "user", "content": "Hello!"}],
)
print(response.choices[0].message.content)

Choose an available protocol for this model. OpenAI SDK uses a Base URL ending in /v1; Anthropic SDK uses the root URL. See each guide for protocol-specific parameters, tools and response formats.

Specifications and interface features

Clarify capacity, inputs and outputs, and invocation methods before selecting a model.

Model positioning: Mythos-class model for general use, including safety safeguards
Input methods: Mixed text and image input
Output methods: Text responses, code, and analysis reports
Access points: Chat Completions or Messages API
Response formats: Refer to the API documentation for standard responses and streaming interactions

Fable 5's image-text understanding and complex reasoning are model capabilities. Input content blocks and streaming events are handled according to the selected public protocol; the application is responsible for retaining relevant history, executing tools, and checking results.

Core capabilities

Learn what claude-fable-5 can bring to your work.

Put complex changes back into the context of the entire project

Fable 5's software engineering strength goes beyond filling in functions; it is better suited to reasoning about cross-file dependencies, architectural constraints, and migration goals. After providing relevant code, error logs, and acceptance criteria, you can have it first analyze the scope of impact, then propose modification plans and testing approaches, reducing cases where only a local issue is fixed while related problems are missed.

Bring screenshots into code and data analysis

It can combine text with interface screenshots, document images, and scientific charts, including extracting numbers from detailed figures and deriving implementation code from page screenshots. It is suitable for submitting visual materials together with requirements, so responses cover both visible information in the image and textual constraints rather than merely summarizing image content.

Continue advancing reasoning around the materials

For long-horizon tasks, Fable 5 can use interim notes to improve subsequent output, making it suitable for repeatedly reviewing assumptions, revising plans, and comparing materials. In practice, you can ask it to record confirmed conclusions, items to verify, and next actions, then continue the analysis as new evidence arrives, keeping complex tasks moving forward with a clear thread.

Applicable Scenarios

Start with specific tasks to identify where the model can be effective.

Code Migration and Refactoring Review

Provide key modules, interface conventions, historical failures, and migration goals, and let Fable 5 organize dependencies, break down the sequence of changes, and produce a risk checklist. Deliverables may include a migration plan, candidate patches, and regression testing recommendations. It is suitable for engineering review first, followed by validation and merging by the development team.

Reviewing Financial and Business Materials

Submit report text, table contents, and chart screenshots together, and ask the model to distinguish facts, assumptions, and inferences, explaining changes in metrics and possible causes. It is suitable for producing an initial analysis draft supported by source materials, a question list, and decision memos; key figures and final conclusions should still be verified against the original materials.

Screenshot-Driven Interface Implementation

Provide target page screenshots, component requirements, and existing code, and let the model analyze layout hierarchy, visual relationships, and interaction requirements before generating implementation recommendations or code. You can also submit design mockups and actual pages side by side to obtain a list of differences and a repair sequence, helping front-end teams turn visual issues into specific engineering tasks.

How to Choose This Model

Choose based on task complexity, input materials, and expected results.

Consider Fable 5 for High Complexity

Compared with Opus 4.8, Fable 5 is more worthwhile for engineering and analysis problems with long spans and many interdependencies. If the current model already reliably completes local modifications or routine document organization, there is no need to replace it across the board; first select the most difficult real-world examples, compare solution completeness, omissions, and the amount of manual rework, then decide the scope of use.

Distinguish Fable, Mythos, and Later Versions

Fable 5 and Mythos 5 use the same base model, but their safety protections and access conditions differ, so Mythos-specific research results cannot be treated directly as a delivery guarantee for Fable. Existing Fable 5 workflows can remain in place; when evaluating Fable 5.1, compare using the same tasks and acceptance criteria rather than replacing it based solely on the version name.

Start with a specific task

Based on the characteristics of claude-fable-5, first validate small tasks whose results can be checked.

Integrated analysis of code and visual materials

You can ask directly: Based on the implementation, design mockups, and research notes, identify conflicting requirements, propose actionable revision plans, and list the materials needed to verify the conclusions.

Prepare inputs that support decisions

Fable and other models are evaluated separately; access eligibility or all safety capabilities cannot be inferred from their relationship to the same base model.

Then integrate it into your workflow

Use the full model ID claude-fable-5, first confirm the public request format and available parameters on the API page, then connect the application. Keep result parsing, exception handling, and relevant evidence, and evaluate with the same set of real samples whether it is suitable for continued use.

Usage boundaries

Before formal use, understand the output quality and capability scope.

Requests related to cybersecurity, biology, chemistry, and model distillation are subject to stricter safety safeguards, and even harmless requests may be restricted. When used in these fields, the legitimate purpose and task boundaries should be clearly stated; it is not advisable to treat it as an automated step that must complete all sensitive procedures.
Long-horizon reasoning does not mean permanent memory, nor does it mean that an entire code repository can be read independently in a single request. Relevant materials need to be submitted, or tools with permitted access need to be configured; ongoing tasks should retain stage summaries, key constraints, and acceptance status to avoid relying on information that has not been explicitly saved.
Reconstructing code from screenshots cannot recover the complete business logic beyond the image, and chart readings are also affected by image clarity. Generated code needs testing, and extracted values need verification; a model proposing an implementation plan does not mean it has run the program, operated the browser, or completed deployment.

Frequently Asked Questions

Answers to common questions about using claude-fable-5.

How do I start calling Claude Fable 5?

Include user and assistant messages relevant to the current task in the messages for Messages or Chat Completions, using the specific format required by the selected public API. Keep the latest code, interim conclusions, and important constraints; when necessary, re-summarize long histories to avoid carrying forward outdated information.

Can I submit code and screenshots at the same time?

Yes. Provide the requirements and code as text, then add image_url image blocks and specify the interface, chart, or issue location you want checked. Fable 5 will analyze the text and images together; small text, scales, and local details in screenshots should remain clear, and important parts can be supplemented with written explanations.

Which entry point should I choose for analyzing PDFs?

Prepare the document text, table data, or clear page screenshots relevant to the question, and specify whether you need a summary, comparison, or extraction of particular information. Submit them in the content formats supported by the selected public API; a PDF address cannot be used as image_url. Require results to retain original text locations, field evidence, and unconfirmed items, and verify key numbers against the source materials.

Does Fable 5 automatically run code and modify repositories?

Generating code and executing code are different steps. Ordinary text-and-image requests can provide analysis and code text; accessing repositories or performing actions requires available tools, appropriate connections, and authorization. Important changes should have human review and testing, and descriptions of completion in responses should not be treated as actual execution records.

Is Fable 5 suitable for replacing all Opus 4.8 tasks?

Not necessarily. Fable 5's value is mainly evident in longer, more complex tasks, such as cross-module migrations, repeatedly revised analyses, and screenshot-driven development. For tasks with a clear scope that are already completed reliably, you can retain the existing workflow and use Fable 5 for difficult cases or critical review steps.

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Output

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claude-fable-5

Flagship model for complex codebases and long-horizon multimodal reasoning

Keep your SDK. Connect in minutes.

Specifications and interface features

Core capabilities

Put complex changes back into the context of the entire project

Bring screenshots into code and data analysis

Continue advancing reasoning around the materials