Anthropic Messages

The Anthropic Messages API provides access to Claude models. It supports both x-api-key header authentication and Bearer Token authentication for flexibility.

Endpoint Info

Item	Value
URL	/v1/messages
Method	POST
Auth	x-api-key header or Bearer Token
Content-Type	application/json
API Version	anthropic-version: 2023-06-01

Authentication

The Anthropic Messages API supports two authentication methods:

Method 1: x-api-key Header (Recommended)

curl https://api.quickapi.store/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: YOUR_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{...}'

Method 2: Bearer Token

curl https://api.quickapi.store/v1/messages \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{...}'

💡 Auth Recommendation

Use the x-api-key header for direct Anthropic SDK integration. Use Bearer Token when routing through OpenAI-compatible middleware or proxies.

Request Parameters

Parameter	Type	Required	Description
model	string	Yes	Model ID, e.g. claude-sonnet-4-20250514
messages	array	Yes	Message array (Anthropic format)
system	string	No	System prompt
max_tokens	integer	Yes	Maximum output tokens (required by Anthropic)
temperature	number	No	Sampling temperature, 0–1. Default 1
top_p	number	No	Nucleus sampling, 0–1
top_k	integer	No	Top-k sampling
stream	boolean	No	Enable streaming. Default false
stop_sequences	array	No	Custom stop sequences
tools	array	No	Tool definitions for tool use
tool_choice	object	No	Tool selection mode

messages Format

Anthropic uses a content array format for messages:

{
  "messages": [
    {
      "role": "user",
      "content": [
        {"type": "text", "text": "Hello, Claude!"}
      ]
    },
    {
      "role": "assistant",
      "content": [
        {"type": "text", "text": "Hello! How can I help you today?"}
      ]
    }
  ]
}

Multimodal with Image

{
  "messages": [
    {
      "role": "user",
      "content": [
        {
          "type": "image",
          "source": {
            "type": "base64",
            "media_type": "image/jpeg",
            "data": "/9j/4AAQSkZJRgABAQAAAQ..."
          }
        },
        {"type": "text", "text": "What is in this image?"}
      ]
    }
  ]
}

cURL Examples

x-api-key Authentication

curl https://api.quickapi.store/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": "Hello, Claude!"}
    ]
  }'

Bearer Token Authentication

curl https://api.quickapi.store/v1/messages \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "claude-sonnet-4-20250514",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "Hello, Claude!"}
    ]
  }'

Streaming Request

curl https://api.quickapi.store/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 haiku about coding"}
    ]
  }'

Multimodal with Image

curl https://api.quickapi.store/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": [
          {
            "type": "image",
            "source": {
              "type": "base64",
              "media_type": "image/jpeg",
              "data": "/9j/4AAQSkZJRgABAQAAAQ..."
            }
          },
          {"type": "text", "text": "Describe this image in detail."}
        ]
      }
    ]
  }'

Response Example

Normal Response

{
  "id": "msg_01Xx7K9qN3vL2mR8p",
  "type": "message",
  "role": "assistant",
  "model": "claude-sonnet-4-20250514",
  "content": [
    {
      "type": "text",
      "text": "Hello! I'm Claude, an AI assistant made by Anthropic. How can I help you today?"
    }
  ],
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "usage": {
    "input_tokens": 12,
    "output_tokens": 24
  }
}

Streaming Response

event: message_start
data: {"type":"message_start","message":{"id":"msg_01Xx7K9qN3vL2mR8p","type":"message","role":"assistant","model":"claude-sonnet-4-20250514","content":[],"stop_reason":null,"stop_sequence":null,"usage":{"input_tokens":12,"output_tokens":1}}}

event: content_block_start
data: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}

event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"Hello"}}

event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"!"}}

event: content_block_stop
data: {"type":"content_block_stop","index":0}

event: message_delta
data: {"type":"message_delta","delta":{"stop_reason":"end_turn","stop_sequence":null},"usage":{"output_tokens":24}}

event: message_stop
data: {"type":"message_stop"}

Python Example

from anthropic import Anthropic

client = Anthropic(
    base_url="https://api.quickapi.store",
    api_key="YOUR_API_KEY"
)

# Normal request
response = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Hello, Claude!"}
    ]
)
print(response.content[0].text)

# Streaming request
with client.messages.stream(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[
        {"role": "user", "content": "Write a haiku about coding"}
    ]
) as stream:
    for text in stream.text_stream:
        print(text, end="")

# Multimodal with image
import base64

with open("image.jpg", "rb") as f:
    image_data = base64.standard_b64encode(f.read()).decode("utf-8")

response = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[
        {
            "role": "user",
            "content": [
                {
                    "type": "image",
                    "source": {
                        "type": "base64",
                        "media_type": "image/jpeg",
                        "data": image_data
                    }
                },
                {"type": "text", "text": "What is in this image?"}
            ]
        }
    ]
)
print(response.content[0].text)

⚠️ max_tokens is Required

Unlike OpenAI's API, Anthropic's Messages API requires the max_tokens parameter. Omitting it will result in a 400 error. Set it to your desired maximum output length.