Anthropic Messages API

Chat with Claude models using the native Anthropic Messages API format

POST /v1/messages

cURL

curl --request POST \
  --url https://toapis.com/v1/messages \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 1024,
    "messages": [
      {
        "role": "user",
        "content": "Hello, tell me about yourself"
      }
    ]
  }'

200

{
  "id": "msg_01XFDUDYJgAACzvnptvVoYEL",
  "type": "message",
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "Hello! I'm Claude, an AI assistant made by Anthropic. I can help with questions, analysis, coding, writing, and more. How can I help you today?"
    }
  ],
  "model": "claude-sonnet-4-6",
  "stop_reason": "end_turn",
  "usage": {
    "input_tokens": 12,
    "output_tokens": 35
  }
}

• Native Anthropic Messages API format
• Drop-in compatible with the official Anthropic SDK (Python / JavaScript) — just change base_url
• Supports streaming (SSE)
• Supports multi-turn conversations, system prompts, vision input, and tool use

If you are already using the OpenAI SDK, use the OpenAI-compatible endpoint instead. If you are using the Anthropic SDK or Claude Code, this endpoint is recommended.

Authorizations

Authorization · string

Bearer token authentication for direct HTTP calls

Authorization: Bearer YOUR_API_KEY

x-api-key · string

API key authentication, compatible with the Anthropic SDK

x-api-key: YOUR_API_KEY

anthropic-version · string · default: "2023-06-01"

Anthropic API version. The Anthropic SDK sets this automatically.

Recommended: 2023-06-01

Body

model · string · required

Model name

All Claude models are supported, for example:

• claude-opus-4-6
• claude-sonnet-4-6
• claude-haiku-4-5

messages · object[] · required

Conversation messages in chronological order. Only user and assistant roles are allowed here — use the top-level system field for system prompts.

Show messages[n]

role · string · required

Message role: user or assistant

content · string | object[] · required

Message content as a string or an array of content blocks

Show Content block

type · string · required

Content type: text or image

text · string

Text content. Required when type is text.

source · object

Image source. Required when type is image.

Show source

type · string · required

Source type: base64 or url

media_type · string

MIME type, required for base64. E.g. image/jpeg, image/png

data · string

Base64-encoded image data. Required when type is base64.

url · string

Image URL. Required when type is url.

max_tokens · integer · required

Maximum number of tokens to generate

• Claude Sonnet 4-6: up to 64000
• Claude Opus 4-6: up to 32000

system · string | object[]

System prompt, set at the top level (not inside messages)

Accepts a plain string or an array of content blocks.

stream · boolean · default: false

Enable streaming output (Server-Sent Events)

• true: tokens streamed incrementally following the Anthropic SSE event format
• false: full response returned at once

temperature · number · default: 1

Sampling temperature controlling output randomness

Range: 0 – 1

top_p · number

Nucleus sampling threshold

Range: 0 – 1. Avoid setting both temperature and top_p simultaneously.

stop_sequences · string[]

Stop sequences — generation stops when any of these strings is produced

Response

id · string

Unique identifier for the request, prefixed with msg_

type · string

Object type, always message

role · string

Response role, always assistant

content · object[]

List of generated content blocks

• content[].type: content type, typically text
• content[].text: generated text

model · string

The model that handled the request

stop_reason · string

Reason generation stopped

• end_turn: model finished naturally
• max_tokens: max_tokens limit reached
• stop_sequence: a stop sequence was triggered

usage · object

Token usage for this request

• usage.input_tokens: input token count
• usage.output_tokens: output token count

cURL

curl --request POST \
  --url https://toapis.com/v1/messages \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 1024,
    "messages": [
      {
        "role": "user",
        "content": "Hello, tell me about yourself"
      }
    ]
  }'

200

{
  "id": "msg_01XFDUDYJgAACzvnptvVoYEL",
  "type": "message",
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "Hello! I'm Claude, an AI assistant made by Anthropic. I can help with questions, analysis, coding, writing, and more. How can I help you today?"
    }
  ],
  "model": "claude-sonnet-4-6",
  "stop_reason": "end_turn",
  "usage": {
    "input_tokens": 12,
    "output_tokens": 35
  }
}