Claude Fable 5
Anthropic's high-capability Fable 5 model for advanced reasoning, repository-scale coding, long-context analysis, and agentic workflows.
claude-fable-5Overview
Advanced reasoning for coding, long context, and agent work
Claude Fable 5 is a high-capability Anthropic model for tasks that need sustained context, careful reasoning, tool-assisted execution, and structured output. It is a good default when the work spans codebases, long documents, visual context, or multi-step agent loops.
Key features
What it is good at
Advanced reasoning
Built for complex analytical, technical, and professional knowledge tasks that need careful multi-step reasoning.
Software engineering workflows
Useful for coding assistance, debugging, refactoring, code review, migration planning, and repository-scale implementation work.
Long-context analysis
Supports extended analysis across large codebases, long documents, and multi-turn work sessions when the platform configuration enables it.
Agentic tool use
A strong fit for tool-assisted workflows that rely on function calling, code execution, MCP, and compatible agent environments.
Multimodal understanding
Supports text and image input for screenshots, documents, diagrams, charts, and other visual materials where available.
Best use cases
Where to use Fable 5
- Large feature work, repository-scale refactors, bug investigation, and code review.
- Extended agent sessions that plan, call tools, verify results, and maintain context over longer work loops.
- Research and knowledge work across technical documents, financial materials, legal text, and structured sources.
- Visual document analysis for screenshots, charts, diagrams, PDFs, and image-based workflow context.
Capabilities
Model limits and support
- Reasoning
- Advanced reasoning for complex professional and technical tasks
- Coding
- Strong coding, debugging, refactoring, and review support
- Agentic workflows
- Suitable for long-running tool and multi-step agent tasks
- Computer use
- Can support browser or desktop interaction through compatible tools
- Multimodal
- Text and image input with text output
- Context window
- Up to 1,000,000 tokens, subject to platform configuration
- Max output
- Up to 128,000 tokens, subject to platform configuration
- Tool use
- Function calling, code execution, MCP, adaptive thinking, and compatible agent workflows
- Multilingual
- Strong performance across major world languages
Known limitations
Operational notes
- Specific capability availability depends on WorldRouter, upstream Anthropic support, plan settings, and rollout status.
- Web access, code execution, computer use, and external actions require compatible tools or integrations.
- Image input is supported, but native audio and video input are not advertised for this model.
- Evaluations, policy behavior, and implementation details may change over time and should not be treated as fixed guarantees.
Quickstart
Call this model
curl https://infer-api-test-46cc90.worldrouter.ai/v1/chat/completions \
-H "Authorization: Bearer your_api_key" \
-H "Content-Type: application/json" \
-d '{
"model": "claude-fable-5",
"messages": [
{
"role": "system",
"content": "You are a precise coding and reasoning assistant."
},
{
"role": "user",
"content": "Review this migration plan and list the riskiest assumptions."
}
],
"max_tokens": 1024,
"temperature": 0.2
}'curl https://infer-api-test-46cc90.worldrouter.ai/v1/messages \
-H "x-api-key: your_api_key" \
-H "anthropic-version: 2023-06-01" \
-H "content-type: application/json" \
-d '{
"model": "claude-fable-5",
"max_tokens": 1024,
"messages": [
{
"role": "user",
"content": "Summarize the key tradeoffs in this architecture decision."
}
]
}'export ANTHROPIC_BASE_URL="https://infer-api-test-46cc90.worldrouter.ai"
export ANTHROPIC_AUTH_TOKEN="your_api_key"
export ANTHROPIC_API_KEY=""
claude --model claude-fable-5 \
"Inspect this repository and propose the smallest safe implementation plan."