Create Message

Endpoint: POST /messages Send a message to Claude via the Messages API.

Most integrations should use Create Chat Completion. Use this endpoint when you specifically need Anthropic’s Messages request format.

import os
import requests

response = requests.post(
    "https://api.yourouter.ai/v1/messages",
    headers={
        "Authorization": f"Bearer {os.environ['YOUROUTER_API_KEY']}",
        "Content-Type": "application/json",
        "anthropic-version": "2023-06-01",
        "vendor": "anthropic"
    },
    json={
        "model": "claude-3-5-sonnet-20240620",
        "messages": [{"role": "user", "content": "Hello"}]
    }
)
print(response.json())

curl https://api.yourouter.ai/v1/messages \
  -H "Authorization: Bearer $YOUROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -H "vendor: anthropic" \
  -d '{"model": "claude-3-5-sonnet-20240620", "messages": [{"role": "user", "content": "Hello"}]}'

Parameters

string

required

Target model ID.

array

required

Conversation history in Claude’s message format.

boolean

default:"false"

If true, results are returned as server-sent events.

Image Input

For Claude vision models, send image content blocks in the messages array.

curl https://api.yourouter.ai/v1/messages \
  -H "Authorization: Bearer $YOUROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -H "vendor: anthropic" \
  -d '{
    "model": "claude-sonnet-4-20250514",
    "max_tokens": 300,
    "messages": [
      {
        "role": "user",
        "content": [
          { "type": "text", "text": "Describe this image in one sentence." },
          {
            "type": "image",
            "source": {
              "type": "base64",
              "media_type": "image/jpeg",
              "data": "<BASE64_IMAGE>"
            }
          }
        ]
      }
    ]
  }'

PDF Input

For Claude models that support PDFs, send a document content block and set source.media_type to application/pdf. The data field contains the base64-encoded raw PDF bytes.

curl https://api.yourouter.ai/v1/messages \
  -H "Authorization: Bearer $YOUROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -H "anthropic-version: 2023-06-01" \
  -H "vendor: anthropic" \
  -d '{
    "model": "claude-sonnet-4-20250514",
    "max_tokens": 1024,
    "messages": [
      {
        "role": "user",
        "content": [
          {
            "type": "document",
            "source": {
              "type": "base64",
              "media_type": "application/pdf",
              "data": "<BASE64_PDF>"
            }
          },
          {
            "type": "text",
            "text": "Summarize this PDF and list risks to watch."
          }
        ]
      }
    ]
  }'

Claude PDF support depends on the specific model. Use standard, unencrypted PDFs and control request body size and page count; split large documents into batches.

See the Multimodal guide for the broader integration path.

Getting Started

Model APIs

Routing & Reliability

API Reference

Features

Legal

Parameters

Image Input

PDF Input

​Parameters

​Image Input

​PDF Input

Parameters

Image Input

PDF Input