Models/Claude Sonnet 4.5 (Thinking)

Claude Sonnet 4.5 (Thinking)

claude-sonnet-4-5-20250929-thinking

Claude Sonnet 4.5 with extended thinking capability for complex reasoning tasks.

Extended ThinkingComplex ReasoningDeep Analysis

Input¥7.35

Output¥36.75

per 1M tokens

Extended Thinking

Advanced reasoning mode

Complex Reasoning

Solve difficult problems

Deep Analysis

Thorough examination

Latest Features

Most recent capabilities

API Documentation

View complete API reference with all parameters and examples.

View Docs

Advanced Features

Streaming

Enable real-time streaming responses with Server-Sent Events.

{
  "model": "claude-sonnet-4-5-20250929-thinking",
  "stream": true,
  "max_tokens": 1024,
  "messages": [...]
}

Function Calling (Tools)

Enable Claude to use tools and call functions.

{
  "model": "claude-sonnet-4-5-20250929-thinking",
  "max_tokens": 1024,
  "tools": [{
    "name": "get_weather",
    "description": "Get current weather for a location",
    "input_schema": {
      "type": "object",
      "properties": {
        "location": {"type": "string", "description": "City name"}
      },
      "required": ["location"]
    }
  }],
  "tool_choice": {"type": "auto"},
  "messages": [{"role": "user", "content": "What's the weather in Tokyo?"}]
}

PDF Support

Analyze PDF documents by sending them as base64 encoded content.

{
  "model": "claude-sonnet-4-5-20250929-thinking",
  "max_tokens": 1024,
  "messages": [{
    "role": "user",
    "content": [{
      "type": "document",
      "source": {
        "type": "base64",
        "media_type": "application/pdf",
        "data": "<base64_encoded_pdf>"
      }
    }, {
      "type": "text",
      "text": "Summarize this document."
    }]
  }]
}

Structured Output (JSON Schema)

Get structured JSON responses that match your schema.

{
  "model": "claude-sonnet-4-5-20250929-thinking",
  "max_tokens": 1024,
  "output_format": {
    "type": "json_schema",
    "schema": {
      "type": "object",
      "properties": {
        "name": {"type": "string"},
        "age": {"type": "integer"}
      },
      "required": ["name", "age"]
    }
  },
  "messages": [{"role": "user", "content": "Extract info: John is 30 years old"}]
}

Web Search

Enable Claude to search the web for up-to-date information.

{
  "model": "claude-sonnet-4-5-20250929-thinking",
  "max_tokens": 1024,
  "tools": [{
    "type": "web_search_20250305",
    "name": "web_search",
    "max_uses": 5
  }],
  "messages": [{"role": "user", "content": "What's the latest news about AI?"}]
}

API Parameters Reference

Parameter	Type	Required	Description
model	string	Yes	Model identifier (e.g., claude-sonnet-4-5-20250929-thinking)
messages	array	Yes	Array of message objects with role and content
max_tokens	integer	Yes	Maximum tokens in the response (1 - 128000)
system	string	No	System prompt to set context
stream	boolean	No	Enable streaming responses (SSE)
temperature	number	No	Sampling temperature (0.0 - 1.0)
top_p	number	No	Nucleus sampling threshold (0.0 - 1.0)
top_k	integer	No	Top-k sampling (0 - infinity)
stop_sequences	array	No	Sequences that stop generation
tools	array	No	Function calling tools definition
tool_choice	object	No	Tool selection strategy (auto/any/tool)
thinking	object	No	Enable extended thinking mode
output_format	object	No	Structured output with JSON schema

Full API Documentation

View complete API reference with streaming, thinking, and more.

View Documentation

Pricing

Input

¥7.35

per 1M tokens

Output

¥36.75

per 1M tokens

Billing: Cost = (input_tokens * input_price + output_tokens * output_price) / 1,000,000