> ## 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 Sonnet 4

> Anthropic's Claude Sonnet 4 via OpenAI-compatible API. The best balance of intelligence and speed for everyday coding and complex tasks.

Claude Sonnet 4 is Anthropic's best coding model, available through Anyfast via an OpenAI-compatible interface. It delivers an ideal balance of intelligence, speed, and cost — excelling at software engineering, complex reasoning, and day-to-day development tasks.

## Key capabilities

* **OpenAI-compatible** — Works as a drop-in replacement with the OpenAI SDK
* **Best coding model** — Top performance on code generation, debugging, and refactoring
* **Fast and efficient** — Lower latency and cost compared to Opus models
* **Strong reasoning** — Excellent at multi-step problem solving and analysis
* **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-sonnet-4-20250514",
      "messages": [
        { "role": "user", "content": "Write a Python function to merge two sorted arrays." }
      ]
    }'
  ```

  ```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-sonnet-4-20250514",
      messages=[
          {"role": "user", "content": "Write a Python function to merge two sorted arrays."}
      ]
  )

  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-sonnet-4-20250514",
      messages=[
          {"role": "user", "content": "Explain the difference between async and sync programming."}
      ],
      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-sonnet-4-20250514`         |
| `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-sonnet-4-20250514">
  View the interactive API playground for Claude Sonnet 4.
</Card>

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