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

# Claude Opus 4.5 Thinking

> Anthropic's Claude Opus 4.5 with extended thinking enabled. The ultimate reasoning model for the most complex problems.

Claude Opus 4.5 Thinking is the extended thinking variant of Claude Opus 4.5, available through Anyfast via an OpenAI-compatible interface. It combines Opus 4.5's unmatched intelligence with step-by-step internal reasoning enabled by default, delivering the highest accuracy available on the most demanding tasks including advanced mathematics, scientific research, and complex architectural decisions.

## Key capabilities

* **OpenAI-compatible** — Works as a drop-in replacement with the OpenAI SDK
* **Extended thinking** — Step-by-step internal reasoning enabled by default
* **Maximum intelligence** — The most capable reasoning model available
* **Deep analysis** — Excels at advanced math, science, and complex problem solving
* **Long context** — Handles large documents and multi-turn conversations
* **Streaming** — Supports real-time token streaming via SSE

## Quick example

<CodeGroup>
  ```bash cURL theme={null}
  curl https://www.anyfast.ai/v1/messages \
    -H "Authorization: Bearer YOUR_API_KEY" \
    -H "Content-Type: application/json" \
    -d '{
      "model": "claude-opus-4-5-20251101-thinking",
      "messages": [
        { "role": "user", "content": "Solve step by step: If a train travels 120 km in 2 hours, then slows down and travels 80 km in 3 hours, what is the average speed for the entire trip?" }
      ]
    }'
  ```

  ```python Python theme={null}
  from openai import OpenAI

  client = OpenAI(
      api_key="YOUR_API_KEY",
      base_url="https://www.anyfast.ai/v1"
  )

  response = client.chat.completions.create(
      model="claude-opus-4-5-20251101-thinking",
      messages=[
          {"role": "user", "content": "Solve step by step: If a train travels 120 km in 2 hours, then slows down and travels 80 km in 3 hours, what is the average speed for the entire trip?"}
      ]
  )

  print(response.choices[0].message.content)
  ```

  ```python Streaming theme={null}
  from openai import OpenAI

  client = OpenAI(
      api_key="YOUR_API_KEY",
      base_url="https://www.anyfast.ai/v1"
  )

  stream = client.chat.completions.create(
      model="claude-opus-4-5-20251101-thinking",
      messages=[
          {"role": "user", "content": "Write a proof that there are infinitely many prime numbers."}
      ],
      stream=True
  )

  for chunk in stream:
      print(chunk.choices[0].delta.content or "", end="")
  ```
</CodeGroup>

## Parameters

| Parameter     | Type           | Required | Description                                 |
| ------------- | -------------- | -------- | ------------------------------------------- |
| `model`       | string         | Yes      | Must be `claude-opus-4-5-20251101-thinking` |
| `messages`    | array          | Yes      | List of `{ role, content }` objects         |
| `max_tokens`  | integer        | No       | Maximum tokens to generate                  |
| `temperature` | float          | No       | `0`–`2`. Controls randomness. Default: `1`  |
| `stream`      | boolean        | No       | Enable SSE streaming. Default: `false`      |
| `top_p`       | float          | No       | Nucleus sampling threshold. Default: `1`    |
| `stop`        | string / array | No       | Sequences that stop generation              |

<Card title="API Reference" icon="code" href="/api-reference/model-api/anthropic/claude-opus-4-5-20251101-thinking">
  View the interactive API playground for Claude Opus 4.5 Thinking.
</Card>

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