Anthropic: Claude Fable 5.2
Claude Fable 5.2 is Anthropic's most capable model for the most demanding technical work, with gains over Fable 5.1 in coding, reasoning, and vision. In prerelease testing it completed otherwise-infeasible software migrations, designed working electronic devices from scratch, and made progress on open problems in physics and mathematics. It communicates more clearly than earlier Fable models and generates output up to 30% faster than Fable 5.1. Adaptive extended thinking is always on, with reasoning effort levels from low to max (default high) and preserved thinking across turns. Anthropic recommends Opus 5.5 as the daily driver for most coding and knowledge work, with Fable 5.2 for the most ambitious, open-ended problems.
Inputs used for the providers' own purposes
At least one provider of this model uses your inputs for its own purposes, for example to train AI models. Do not enter personal data of third parties or sensitive data. You can object to this use at any time in your account settings or via "Manage consents" in the chat.
Read the privacy policyPricing
Uptime
Performance
Usage & Ranking
Supported parameters
All providers = every upstream serving this model supports it. Some providers = depends on which upstream handles the request. Default = the value sent when you leave the parameter unset.
| Parameter | Providers | Default |
|---|---|---|
| include_reasoning | All providers | - |
| max_completion_tokens | Some providers | - |
| max_tokens | All providers | - |
| reasoning | All providers | - |
| reasoning_effort | All providers | - |
| response_format | All providers | - |
| stop | All providers | - |
| structured_outputs | All providers | - |
| tool_choice | All providers | - |
| tools | All providers | - |
| verbosity | All providers | - |
Frequently asked questions
Use claude-fable-5.2 in
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Base URL
https://api.unorouter.com/v1Call claude-fable-5.2 from your code
Point any OpenAI-compatible SDK at UnoRouter and request the model by name. Replace YOUR_API_KEY with a real key from your dashboard.
curl https://api.unorouter.com/v1/chat/completions \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "claude-fable-5.2",
"messages": [{"role": "user", "content": "Hello!"}]
}'