Claude Native Format

Call Claude models using the Anthropic native Messages API format, supporting streaming, Function Calling, and Extended Thinking

Claude Native Format

POST /v1/messages

Crazyrouter supports Anthropic’s native Messages API format. You can pass the API Key using either the x-api-key or Authorization header.

Authentication

Two authentication methods are supported (choose one):

x-api-key: YOUR_API_KEY

Authorization: Bearer YOUR_API_KEY

---

Basic Conversation

cURL

curl https://crazyrouter.com/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: YOUR_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "claude-sonnet-4-20250514",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "Explain quantum computing in simple terms"}
    ]
  }'

Request Parameters

Parameter	Type	Required	Description
model	string	Yes	Model name
max_tokens	integer	Yes	Maximum output tokens
messages	array	Yes	Message list
system	string|array	No	System prompt
temperature	number	No	Sampling temperature, 0-1
top_p	number	No	Nucleus sampling parameter
top_k	integer	No	Top-K sampling
stop_sequences	array	No	Stop sequence list
stream	boolean	No	Whether to stream output
tools	array	No	Tool definition list
tool_choice	object	No	Tool selection strategy
thinking	object	No	Extended Thinking configuration

---

Streaming Conversation

cURL

curl https://crazyrouter.com/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: YOUR_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "claude-sonnet-4-20250514",
    "max_tokens": 1024,
    "stream": true,
    "messages": [
      {"role": "user", "content": "Write a poem about programming"}
    ]
  }'

---

Function Calling

Python

import anthropic
import json

client = anthropic.Anthropic(
    api_key="YOUR_API_KEY",
    base_url="https://crazyrouter.com"
)

tools = [
    {
        "name": "get_stock_price",
        "description": "Get the current price of a specified stock",
        "input_schema": {
            "type": "object",
            "properties": {
                "symbol": {
                    "type": "string",
                    "description": "Stock ticker symbol, e.g. AAPL, GOOGL"
                }
            },
            "required": ["symbol"]
        }
    }
]

# First call
message = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    tools=tools,
    messages=[
        {"role": "user", "content": "What is Apple's stock price?"}
    ]
)

# Handle tool call
if message.stop_reason == "tool_use":
    tool_block = next(b for b in message.content if b.type == "tool_use")

    # Execute function
    result = {"symbol": "AAPL", "price": 198.50, "currency": "USD"}

    # Second call, return function result
    final = client.messages.create(
        model="claude-sonnet-4-20250514",
        max_tokens=1024,
        tools=tools,
        messages=[
            {"role": "user", "content": "What is Apple's stock price?"},
            {"role": "assistant", "content": message.content},
            {
                "role": "user",
                "content": [
                    {
                        "type": "tool_result",
                        "tool_use_id": tool_block.id,
                        "content": json.dumps(result)
                    }
                ]
            }
        ]
    )
    print(final.content[0].text)

---

Extended Thinking

Enable Extended Thinking to let Claude perform deep thinking before answering:

cURL

curl https://crazyrouter.com/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: YOUR_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "claude-sonnet-4-20250514",
    "max_tokens": 16000,
    "thinking": {
      "type": "enabled",
      "budget_tokens": 10000
    },
    "messages": [
      {"role": "user", "content": "Analyze the time complexity of the following code and propose an optimization:\ndef fib(n):\n    if n <= 1: return n\n    return fib(n-1) + fib(n-2)"}
    ]
  }'

Extended Thinking Response

{
  "id": "msg_abc123",
  "type": "message",
  "role": "assistant",
  "content": [
    {
      "type": "thinking",
      "thinking": "Let me use mathematical induction to prove this...\nBase case: when n=1..."
    },
    {
      "type": "text",
      "text": "I will prove this formula using mathematical induction.\n\n**Base case**: ..."
    }
  ],
  "model": "claude-sonnet-4-20250514",
  "stop_reason": "end_turn",
  "usage": {
    "input_tokens": 30,
    "output_tokens": 500
  }
}

When using Extended Thinking, max_tokens must be greater than budget_tokens. Thinking tokens are also billed.

Crazyrouter’s Claude native format endpoint is fully compatible with the official Anthropic SDK. Simply change the base_url for seamless switching.