POST
/
v1
/
messages
Create message
curl --request POST \
  --url https://router.requesty.ai/v1/messages \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <x-api-key>' \
  --data '{
  "model": "anthropic/claude-sonnet-4-20250514",
  "max_tokens": 1024,
  "messages": [
    {
      "role": "user",
      "content": "<string>"
    }
  ],
  "system": "<string>",
  "temperature": 1,
  "top_p": 0.5,
  "top_k": 1,
  "stream": true,
  "stop_sequences": [
    "<string>"
  ],
  "tools": [
    {
      "name": "<string>",
      "description": "<string>",
      "input_schema": {}
    }
  ],
  "tool_choice": "auto"
}'
{
  "id": "<string>",
  "type": "message",
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "<string>"
    }
  ],
  "model": "<string>",
  "stop_reason": "end_turn",
  "stop_sequence": "<string>",
  "usage": {
    "input_tokens": 123,
    "output_tokens": 123
  }
}
Send a message to an Anthropic-compatible model and receive a response. This endpoint follows the Anthropic Messages API format and supports all Anthropic models as well as compatible models from other providers through Requesty’s routing.

​
Base URL

https://router.requesty.ai/v1/messages

​
Authentication

Include your Requesty API key in the request headers using Anthropic’s standard format: 
x-api-key: YOUR_REQUESTY_API_KEY

​
Headers

HeaderRequiredDescription
x-api-key✅Your Requesty API key (Anthropic format)
Content-Type✅Must be application/json
anthropic-version❌API version (defaults to 2023-06-01)

​
Example Request

curl https://router.requesty.ai/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: YOUR_REQUESTY_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -d '{
    "model": "anthropic/claude-sonnet-4-20250514",
    "max_tokens": 1024,
    "messages": [
      {
        "role": "user",
        "content": "Hello, Claude!"
      }
    ]
  }'

​
Model Selection

You can use any model available in the Model Library. Examples:
  • Anthropic Models: anthropic/claude-sonnet-4-20250514, anthropic/claude-3-7-sonnet
  • OpenAI Models: openai/gpt-4o, openai/gpt-4o-mini
  • Google Models: google/gemini-2.0-flash-exp
  • Other Providers: mistral/mistral-large-2411, meta/llama-3.3-70b-instruct
While this endpoint uses the Anthropic Messages format, Requesty automatically handles format conversion for non-Anthropic models, so you can use any supported model with this endpoint.

​
Streaming

Enable streaming responses by setting stream: true: 
{
	"model": "anthropic/claude-sonnet-4-20250514",
	"max_tokens": 1024,
	"stream": true,
	"messages": [
		{
			"role": "user",
			"content": "Write a short story"
		}
	]
}

​
Vision Support

Send images using the content blocks format: 
{
	"model": "anthropic/claude-sonnet-4-20250514",
	"max_tokens": 1024,
	"messages": [
		{
			"role": "user",
			"content": [
				{
					"type": "text",
					"text": "What do you see in this image?"
				},
				{
					"type": "image",
					"source": {
						"type": "base64",
						"media_type": "image/jpeg",
						"data": "/9j/4AAQSkZJRgABAQAAAQABAAD..."
					}
				}
			]
		}
	]
}

​
PDF Support

You can send PDFs, encoded in base 64 format: 
{
	"model": "anthropic/claude-sonnet-4-20250514",
	"max_tokens": 1024,
	"messages": [
		{
			"role": "user",
			"content": [
				{
					"type": "text",
					"text": "What is in this PDF?"
				},
                {
                    "type": "document",
                    "source": {
                        "type": "base64",
                        "media_type": "application/pdf",
                        "data": "JVBERi0=..."
                    }
				}
			]
		}
	]
}

​
Tool Use

Define tools that the model can call: 
{
	"model": "anthropic/claude-sonnet-4-20250514",
	"max_tokens": 1024,
	"tools": [
		{
			"name": "get_weather",
			"description": "Get the current weather in a given location",
			"input_schema": {
				"type": "object",
				"properties": {
					"location": {
						"type": "string",
						"description": "The city and state, e.g. San Francisco, CA"
					}
				},
				"required": ["location"]
			}
		}
	],
	"messages": [
		{
			"role": "user",
			"content": "What's the weather like in New York?"
		}
	]
}

​
System Prompts

Include system instructions using the system parameter: 
{
	"model": "anthropic/claude-sonnet-4-20250514",
	"max_tokens": 1024,
	"system": "You are a helpful assistant that always responds in a friendly, professional manner.",
	"messages": [
		{
			"role": "user",
			"content": "Hello!"
		}
	]
}

​
Error Handling

The API returns standard HTTP status codes:
  • 200 - Success
  • 400 - Bad Request (invalid parameters)
  • 401 - Unauthorized (invalid API key)
  • 403 - Forbidden (insufficient permissions)
  • 429 - Rate Limited
  • 500 - Internal Server Error
Example error response: 
{
	"error": {
		"type": "invalid_request_error",
		"message": "max_tokens is required"
	}
}

​
Response Format

Successful responses follow the Anthropic Messages format: 
{
	"id": "msg_01ABC123",
	"type": "message",
	"role": "assistant",
	"content": [
		{
			"type": "text",
			"text": "Hello! I'm Claude, an AI assistant. How can I help you today?"
		}
	],
	"model": "anthropic/claude-sonnet-4-20250514",
	"stop_reason": "end_turn",
	"usage": {
		"input_tokens": 12,
		"output_tokens": 18
	}
}

​
Key Differences from OpenAI Chat Completions

  • Authentication: Uses x-api-key header instead of Authorization: Bearer
  • Required max_tokens: Unlike OpenAI’s API, the max_tokens parameter is required
  • Content Blocks: Messages use content blocks for rich content (text, images, tool calls)
  • System Parameter: System prompts are specified as a separate system parameter, not as a message
  • Role Restrictions: Only user and assistant roles are supported in messages (no system role)
For the most seamless experience with Anthropic models, use this endpoint. For broader compatibility across all providers, consider using the Chat Completions endpoint instead.

Headers

​
x-api-key
string
required

Your Requesty API key

​
anthropic-version
string
default:2023-06-01

The version of the Anthropic API to use

Example:

"2023-06-01"

Body

application/json
​
model
string
default:anthropic/claude-sonnet-4-20250514
required

The model to use for the completion

Example:

"anthropic/claude-sonnet-4-20250514"

​
max_tokens
integer
required

The maximum number of tokens to generate before stopping

Required range: x >= 1
Example:

1024

​
messages
object[]
required

Input messages

​
system
string

System prompt to be used for the completion

​
temperature
number

Amount of randomness injected into the response

Required range: 0 <= x <= 2
​
top_p
number

Use nucleus sampling

Required range: 0 <= x <= 1
​
top_k
integer

Only sample from the top K options for each subsequent token

Required range: x >= 0
​
stream
boolean

Whether to incrementally stream the response using server-sent events

​
stop_sequences
string[]

Custom text sequences that will cause the model to stop generating

​
tools
object[]

Definitions of tools that the model may use

​
tool_choice

How the model should use the provided tools

Available options:
auto,
any

Response

Message response

​
id
string
required

Unique object identifier

​
type
enum<string>
required

Object type

Available options:
message
​
role
enum<string>
required

Conversational role of the generated message

Available options:
assistant
​
content
object[]
required

Content generated by the model

​
model
string
required

The model that handled the request

​
stop_reason
enum<string>
required

The reason that we stopped

Available options:
end_turn,
max_tokens,
stop_sequence,
tool_use
​
usage
object
required
​
stop_sequence
string

Which custom stop sequence was generated