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

# Claude Sonnet 4.5 Thinking

> Anthropic's Claude Sonnet 4.5 with Extended Thinking — enhanced reasoning at the speed and capability of the best coding model.

Claude Sonnet 4.5 Thinking is the Extended Thinking version of Claude Sonnet 4.5, available through Starrise AI via OpenAI-compatible interface. Combining Sonnet 4.5's excellent balance of speed and capability with step-by-step internal reasoning enabled by default, it significantly improves accuracy on complex tasks while maintaining fast response times.

## Key Capabilities

* **OpenAI-compatible** — Drop-in replacement for the OpenAI SDK, no other code changes needed
* **Extended Thinking** — Step-by-step internal reasoning enabled by default
* **Best coding model** — Top-performing for code generation, refactoring, and debugging
* **Enhanced reasoning** — Significantly improved accuracy on complex multi-step tasks
* **Long context** — Supports large document processing and multi-turn conversations
* **Streaming** — Real-time token streaming via SSE

## Quick Example

<CodeGroup>
  ```bash cURL theme={null}
  curl https://ai.alad.com/v1/messages \
    -H "Authorization: Bearer YOUR_API_KEY" \
    -H "Content-Type: application/json" \
    -d '{
      "model": "claude-sonnet-4-5-20250929-thinking",
      "messages": [
        { "role": "user", "content": "Solve step by step: 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 journey?" }
      ]
    }'
  ```

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

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

  response = client.chat.completions.create(
      model="claude-sonnet-4-5-20250929-thinking",
      messages=[
          {"role": "user", "content": "Solve step by step: 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 journey?"}
      ]
  )

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

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

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

  stream = client.chat.completions.create(
      model="claude-sonnet-4-5-20250929-thinking",
      messages=[
          {"role": "user", "content": "Prove 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      | Fixed value: `claude-sonnet-4-5-20250929-thinking` |
| `messages`    | array          | Yes      | Array of `{ role, content }` objects               |
| `max_tokens`  | integer        | No       | Maximum number of 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 where generation stops                   |

<Card title="API Reference" icon="code" href="/en/api-reference/model-api/anthropic/claude-sonnet-4-5-20250929-thinking">
  View the interactive API Playground for Claude Sonnet 4.5 Thinking.
</Card>