Messages API

Messages API is a compatibility surface for Anthropic-style clients. For new LLM integrations without that requirement, prefer Responses API.

Use this API when your tooling already expects Anthropic-style content blocks, tool use blocks, and Messages streaming events. If you are starting a new integration and do not need Anthropic compatibility, use Responses API.

Best Fit

Anthropic-compatible SDKs and wrappers
agent frameworks that already target the Messages protocol
applications built around block-typed content instead of plain assistant strings

When to stay on Messages

your SDK or agent stack already depends on Anthropic block semantics
you need tool_use, tool_result, and thinking blocks in their Anthropic-style form
migration cost is higher than the benefit of switching to Responses right now

Request Model

Common fields include:

model
max_tokens
messages
system
tools
thinking
output_config
stream

Quick Example

from anthropic import Anthropic

client = Anthropic(
    base_url="https://api.naga.ac",
    api_key="YOUR_API_KEY",
)

message = client.messages.create(
    model="claude-sonnet-4.5",
    max_tokens=256,
    messages=[
        {
            "role": "user",
            "content": "Explain circuit breakers in simple terms.",
        }
    ],
)

print(message.content[0].text)

import Anthropic from '@anthropic-ai/sdk';

const client = new Anthropic({
  baseURL: 'https://api.naga.ac',
  apiKey: 'YOUR_API_KEY',
});

const message = await client.messages.create({
  model: 'claude-sonnet-4.5',
  max_tokens: 256,
  messages: [
    { role: 'user', content: 'Explain circuit breakers in simple terms.' },
  ],
});

console.log(message.content[0].text);

curl https://api.naga.ac/v1/messages \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4.5",
    "max_tokens": 256,
    "messages": [
      {
        "role": "user",
        "content": [
          {"type": "text", "text": "Explain circuit breakers in simple terms."}
        ]
      }
    ]
  }'

Response Model

Successful responses follow the Anthropic message shape.

{
  "type": "message",
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "Circuit breakers stop repeated failing calls so the rest of the system can recover."
    }
  ],
  "stop_reason": "end_turn"
}

Common mistakes

starting a new project on Messages when Anthropic compatibility is not required
assuming Messages blocks map 1:1 to Responses items without adaptation
forgetting that this is a compatibility surface over the same underlying platform

Learn The API In Detail

Streaming

Handle Anthropic-style event streams and final usage data.

Tool Use

Work with tool_use and tool_result blocks.

Thinking Blocks

Understand reasoning controls and thinking block semantics.

Web Search

Enable search-aware behavior in the Messages compatibility layer.

Documents and PDFs

Send document blocks and PDF sources in Anthropic-style content.

Migration to Responses

Move from Messages blocks to the Responses item model.

Reference

Create message

Get Started

Build

API Guides

Account

Product

Best Fit

When to stay on Messages

Request Model

Quick Example

Response Model

Common mistakes

Learn The API In Detail

Streaming

Tool Use

Thinking Blocks

Web Search

Documents and PDFs

Migration to Responses

Reference

​Best Fit

​When to stay on Messages

​Request Model

​Quick Example

​Response Model

​Common mistakes

​Learn The API In Detail

Streaming

Tool Use

Thinking Blocks

Web Search

Documents and PDFs

Migration to Responses

​Reference

Best Fit

When to stay on Messages

Request Model

Quick Example

Response Model

Common mistakes

Learn The API In Detail

Reference