> ## Documentation Index
> Fetch the complete documentation index at: https://docs.unifically.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Claude Fable 5.1

> Anthropic's Claude Fable 5.1 language model. See supported inputs, parameters, pricing, response fields, and API examples.

Claude Fable 5.1 is Anthropic's top Claude 5 family model, built for long-running agentic coding, multistep research, and document, spreadsheet, and slide work. It takes text and image input, outputs text, and carries a 1M token context window with up to 128k output tokens. Adaptive thinking is always on.

## Model

```
anthropic/claude-fable-5-1
```

|                    |                  |
| ------------------ | ---------------- |
| **Provider**       | Anthropic        |
| **Name**           | Claude Fable 5.1 |
| **Context window** | 1M tokens        |
| **Max output**     | 128k tokens      |

## Supported Endpoints

All three API formats are supported:

* [Chat Completions](/api-reference/v1-chat-completions) — `POST /v1/chat/completions`
* [Responses](/api-reference/v1-responses) — `POST /v1/responses`
* [Messages](/api-reference/v1-messages) — `POST /v1/messages`

## Example

```bash theme={null}
curl -X POST https://api.unifically.com/v1/messages \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -d '{
    "model": "anthropic/claude-fable-5-1",
    "max_tokens": 4096,
    "messages": [
      {"role": "user", "content": "This service crashes about once in a million runs. Here are the logs. Find the root cause."}
    ]
  }'
```

<Note>
  Forced tool use (`tool_choice` set to `any` or a named tool) is not supported on this model and returns a 400. Keep `tool_choice` on `auto` and name the tool in the prompt. Thinking blocks are bound to the model that produced them, so keep conversation history append-only.
</Note>

<Note>
  **Volume discounts** are available for almost all models. Reach out at [contact@unifically.com](mailto:contact@unifically.com) to discuss custom pricing.
</Note>