> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://respan.ai/docs/apis/gateway/create-anthropic-message/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://respan.ai/_mcp/server.

# Create an Anthropic message

POST https://api.respan.ai/api/anthropic/v1/messages
Content-Type: application/json

Send native Anthropic Messages requests through Respan using provider credentials configured in Respan. Authenticate with your Respan key in `x-api-key` for Anthropic SDKs or `Authorization: Bearer` for bearer clients.

Reference: https://respan.ai/docs/apis/gateway/create-anthropic-message

## Request

### Headers

- `x-api-key` (string, required) — Your Respan API key in Anthropic's native authentication header. Bearer authentication is also accepted.
- `anthropic-version` (string, optional, default: 2023-06-01)
- `anthropic-beta` (string, optional)

### Body (application/json)

This endpoint expects an object.

- `model` (string, required)
- `max_tokens` (integer, required)
- `messages` (list of map from string to any, required)
- `stream` (boolean, optional, default: false)
- `respan_params` (map from string to any, optional)

## Response

### 200

Anthropic response or event stream.

- `map from string to any`

## Errors

### 400 Bad Request Error

Invalid request.

- `map from string to any`

### 402 Payment Required Error

Insufficient credits.

- `map from string to any`

### 403 Forbidden Error

The API key is missing, invalid or expired.

- `detail` (string, required)

### 424 Failed Dependency Error

Upstream provider failed.

- `map from string to any`

### 429 Too Many Requests Error

Rate limit exceeded.

- `map from string to any`

## Examples

**Request**

```json
{
  "model": "claude-sonnet-4-5-20250929",
  "max_tokens": 64,
  "messages": [
    {
      "role": "user",
      "content": "Explain how AI works in a few words."
    }
  ]
}
```

**Response**

```json
{
  "id": "msg_example",
  "type": "message",
  "role": "assistant",
  "model": "claude-sonnet-4-5-20250929",
  "content": [
    {
      "type": "text",
      "text": "AI learns patterns from data to make predictions and generate responses."
    }
  ],
  "stop_reason": "end_turn",
  "stop_sequence": null
}
```

**SDK Code**

```python Anthropic Gateway_api_anthropic_v1_messages_create_example
import requests

url = "https://api.respan.ai/api/anthropic/v1/messages"

payload = {
    "model": "claude-sonnet-4-5-20250929",
    "max_tokens": 64,
    "messages": [
        {
            "role": "user",
            "content": "Explain how AI works in a few words."
        }
    ]
}
headers = {
    "x-api-key": "YOUR_RESPAN_API_KEY",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.json())
```

```javascript Anthropic Gateway_api_anthropic_v1_messages_create_example
const url = 'https://api.respan.ai/api/anthropic/v1/messages';
const options = {
  method: 'POST',
  headers: {'x-api-key': 'YOUR_RESPAN_API_KEY', 'Content-Type': 'application/json'},
  body: '{"model":"claude-sonnet-4-5-20250929","max_tokens":64,"messages":[{"role":"user","content":"Explain how AI works in a few words."}]}'
};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```

```go Anthropic Gateway_api_anthropic_v1_messages_create_example
package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.respan.ai/api/anthropic/v1/messages"

	payload := strings.NewReader("{\n  \"model\": \"claude-sonnet-4-5-20250929\",\n  \"max_tokens\": 64,\n  \"messages\": [\n    {\n      \"role\": \"user\",\n      \"content\": \"Explain how AI works in a few words.\"\n    }\n  ]\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("x-api-key", "YOUR_RESPAN_API_KEY")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(res)
	fmt.Println(string(body))

}
```

```ruby Anthropic Gateway_api_anthropic_v1_messages_create_example
require 'uri'
require 'net/http'

url = URI("https://api.respan.ai/api/anthropic/v1/messages")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["x-api-key"] = 'YOUR_RESPAN_API_KEY'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"model\": \"claude-sonnet-4-5-20250929\",\n  \"max_tokens\": 64,\n  \"messages\": [\n    {\n      \"role\": \"user\",\n      \"content\": \"Explain how AI works in a few words.\"\n    }\n  ]\n}"

response = http.request(request)
puts response.read_body
```

```java Anthropic Gateway_api_anthropic_v1_messages_create_example
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api.respan.ai/api/anthropic/v1/messages")
  .header("x-api-key", "YOUR_RESPAN_API_KEY")
  .header("Content-Type", "application/json")
  .body("{\n  \"model\": \"claude-sonnet-4-5-20250929\",\n  \"max_tokens\": 64,\n  \"messages\": [\n    {\n      \"role\": \"user\",\n      \"content\": \"Explain how AI works in a few words.\"\n    }\n  ]\n}")
  .asString();
```

```php Anthropic Gateway_api_anthropic_v1_messages_create_example
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api.respan.ai/api/anthropic/v1/messages', [
  'body' => '{
  "model": "claude-sonnet-4-5-20250929",
  "max_tokens": 64,
  "messages": [
    {
      "role": "user",
      "content": "Explain how AI works in a few words."
    }
  ]
}',
  'headers' => [
    'Content-Type' => 'application/json',
    'x-api-key' => 'YOUR_RESPAN_API_KEY',
  ],
]);

echo $response->getBody();
```

```csharp Anthropic Gateway_api_anthropic_v1_messages_create_example
using RestSharp;

var client = new RestClient("https://api.respan.ai/api/anthropic/v1/messages");
var request = new RestRequest(Method.POST);
request.AddHeader("x-api-key", "YOUR_RESPAN_API_KEY");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"model\": \"claude-sonnet-4-5-20250929\",\n  \"max_tokens\": 64,\n  \"messages\": [\n    {\n      \"role\": \"user\",\n      \"content\": \"Explain how AI works in a few words.\"\n    }\n  ]\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift Anthropic Gateway_api_anthropic_v1_messages_create_example
import Foundation

let headers = [
  "x-api-key": "YOUR_RESPAN_API_KEY",
  "Content-Type": "application/json"
]
let parameters = [
  "model": "claude-sonnet-4-5-20250929",
  "max_tokens": 64,
  "messages": [
    [
      "role": "user",
      "content": "Explain how AI works in a few words."
    ]
  ]
] as [String : Any]

let postData = JSONSerialization.data(withJSONObject: parameters, options: [])

let request = NSMutableURLRequest(url: NSURL(string: "https://api.respan.ai/api/anthropic/v1/messages")! as URL,
                                        cachePolicy: .useProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.httpMethod = "POST"
request.allHTTPHeaderFields = headers
request.httpBody = postData as Data

let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
  if (error != nil) {
    print(error as Any)
  } else {
    let httpResponse = response as? HTTPURLResponse
    print(httpResponse)
  }
})

dataTask.resume()
```