Requesty normalizes the schema across models and providers, so you don’t waste time with custom integrations.

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Request Structure

Your request body to /v1/chat/completions closely follows the OpenAI Chat Completion schema:
  • Required Fields:
    • messages: An array of message objects with role and content
    • Roles can be user, assistant, system, or tool
    • model: The model name. If omitted, defaults to the user’s or payer’s default model. Here is a full list of the supported models
  • Optional Fields:
    • prompt: Alternative to messages for some providers.
    • stream: A boolean to enable Server-Sent Events (SSE) streaming responses.
    • max_tokens, temperature, top_p, etc.: Standard language model parameters.
    • tools / functions : Allows function calling with a schema defined. See OpenAI’s function calling documentation for the structure of these requests.
    • tool_choice : Specifies how tool calling should be handled.
    • response_format : For structured responses (some models only).

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Example Request Body

{
  "model": "openai/gpt-4o-mini",
  "messages": [
    {"role": "system", "content": "You are a helpful assistant."},
    {"role": "user", "content": "What is the capital of France?"}
  ],
  "max_tokens": 200,
  "temperature": 0.7,
  "stream": true,
  "tools": [
    {
      "type": "function",
      "function": {
        "name": "get_current_weather",
        "description": "Get the current weather in a given location",
        "parameters": {
          "type": "object",
          "properties": {
            "location": {"type": "string", "description": "City and state"},
            "unit": {"type": "string", "enum": ["celsius", "fahrenheit"]}
          },
          "required": ["location"]
        }
      }
    }
  ]
}
Here, we also provide a tool (get_current_weather) that the model can call if it decides the user request involves weather data. Some request fields require a different function, for example if you use response_format you’ll need to update the request to client.beta.chat.completions.parse and you may want to use the Pydantic or Zod format for your structure.

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Response Structure

The response is normalized to an OpenAI-style ChatCompletion object:
  1. Streaming: If stream: true, responses arrive incrementally as SSE events with data: lines. See Streaming for documentation on streaming.
  2. Function Calls (Tool Calls): If the model decides to call a tool, it will return a function_call in the assistant message. You then execute the tool, append the tool’s result as a role: "tool" message, and send a follow-up request. The LLM will then integrate the tool output into its final answer.

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Non-Streaming Response Example

{
  "id": "chatcmpl-xyz123",
  "object": "chat.completion",
  "created": 1687623702,
  "model": "openai/gpt-4o",
  "usage": {
    "prompt_tokens": 10,
    "completion_tokens": 50,
    "total_tokens": 60
  },
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": "The capital of France is Paris."
      },
      "finish_reason": "stop"
    }
  ]
}
Function Call Example: If the model decides it needs the weather tool: 
{
  "id": "chatcmpl-abc456",
  "object": "chat.completion",
  "created": 1687623800,
  "model": "openai/gpt-4o",
  "choices": [
    {
      "index": 0,
      "message": {
        "role": "assistant",
        "content": null,
        "function_call": {
          "name": "get_current_weather",
          "arguments": "{ "location": "Boston, MA"}"
        }
      },
      "finish_reason": "function_call"
    }
  ]
}
You would then call the get_current_weather function externally, get the result, and send it back as: 
{
  "model": "openai/gpt-4o",
  "messages": [
    {"role": "user", "content": "What is the weather in Boston?"},
    {
      "role": "assistant",
      "content": null,
      "function_call": {
        "name": "get_current_weather",
        "arguments": "{ "location": "Boston, MA" }"
      }
    },
    {
      "role": "tool",
      "name": "get_current_weather",
      "content": "{"temperature": "22", "unit": "celsius", "description": "Sunny"}"
    }
  ]
}
The next completion will return a final answer integrating the tool’s response.