Responses API

FastRouter's Responses API provides a unified interface for generating model responses, invoking tools, handling conversation context, streaming output, and engaging with multiple model providers.

The Responses API is FastRouter’s unified interface for generating model responses, calling tools/functions, handling prior conversation context, streaming output, and interacting with multiple model providers like OpenAI, Azure (for OpenAI models) and X-AI (for Grok models) — all through a single endpoint.

---

Endpoint

POST https://go.fastrouter.ai/api/v1/responses

Base URL

https://go.fastrouter.ai/api/v1

---

Basic Usage (OpenAI / Azure Providers)

Example: Simple Text Response

curl --location 'https://go.fastrouter.ai/api/v1/responses' \
--header 'Authorization: Bearer API-KEY' \
--header 'Content-Type: application/json' \
--data '{
    "model": "openai/o3",
    "input": "Tell me a three sentence bedtime story about a unicorn.",
    "stream": false
}'

Sample Response

{
  "background": false,
  "created_at": 1764138326,
  "error": null,
  "id": "fr_ID123",
  "model": "o3-2025-04-16",
  "object": "response",
  "output": [
    {
      "id": "rs_ID123",
      "summary": [],
      "type": "reasoning"
    },
    {
      "id": "msg_ID123",
      "role": "assistant",
      "type": "message",
      "status": "completed",
      "content": [
        {
          "type": "output_text",
          "text": "Under a silvery moon, a gentle unicorn named Liora tiptoed..."
        }
      ]
    }
  ],
  ...
}

---

Python Example Using OpenAI SDK

from openai import OpenAI

client = OpenAI(
    api_key="API-KEY",
    base_url="https://go.fastrouter.ai/api/v1"
)

response = client.responses.create(
    model="openai/o3",
    input="Tell me a three sentence bedtime story about a unicorn."
)

print(response.output_text)

---

Using a Previous Response ID (Thread Continuity)

curl --location 'https://go.fastrouter.ai/api/v1/responses' \
--header 'Authorization: Bearer API-KEY' \
--header 'Content-Type: application/json' \
--data '{
    "model": "openai/o3",
    "input": "Replace the word unicorn with a horse.",
    "previous_response_id": "fr_ID123"
}'

---

Function Calling

curl --location 'https://go.fastrouter.ai/api/v1/responses' \
--header 'Authorization: Bearer API-KEY' \
--header 'Content-Type: application/json' \
--data '{
    "model": "openai/gpt-4.1",
    "input": "What is the weather like in Boston today?",
    "tools": [
        {
            "type": "function",
            "name": "get_current_weather",
            "description": "Get the current weather in a given location",
            "parameters": {
                "type": "object",
                "properties": {
                    "location": {
                        "type": "string",
                        "description": "The city and state"
                    },
                    "unit": {
                        "type": "string",
                        "enum": ["celsius", "fahrenheit"]
                    }
                },
                "required": ["location", "unit"]
            }
        }
    ],
    "tool_choice": "auto"
}'

---

Web Search Tool Calling

curl --location 'https://go.fastrouter.ai/api/v1/responses' \
--header 'Authorization: Bearer API-KEY' \
--header 'Content-Type: application/json' \
--data '{
    "model": "openai/gpt-4.1",
    "tools": [
        {
            "type": "web_search",
            "filters": {
                "allowed_domains": ["pubmed.ncbi.nlm.nih.gov"]
            }
        }
    ],
    "input": "What are the top 5 medical breakthroughs?"
}'

---

File Input Example

curl --location 'https://go.fastrouter.ai/api/v1/responses' \
--header 'Authorization: Bearer API-KEY' \
--header 'Content-Type: application/json' \
--data '{
    "model": "openai/gpt-4.1",
    "input": [
      {
        "role": "user",
        "content": [
          {"type": "input_text", "text": "What is in this file?"},
          {
            "type": "input_file",
            "file_url": "https://www.berkshirehathaway.com/letters/2024ltr.pdf"
          }
        ]
      }
    ]
}'

---

Grok Provider Examples

Basic Grok Request

curl --location 'https://go.fastrouter.ai/api/v1/responses' \
--header 'Authorization: Bearer API-KEY' \
--header 'Content-Type: application/json' \
--data '{
    "model": "x-ai/grok-4",
    "input": "Tell me a fact about pineapples"
}'

Using Previous Response ID

curl --location 'https://go.fastrouter.ai/api/v1/responses' \
--header 'Authorization: Bearer API_KEY' \
--header 'Content-Type: application/json' \
--data '{
    "model": "x-ai/grok-4",
    "input": "Tell me one more",
    "previous_response_id": "fr_123"
}'

Streaming Responses

curl --location 'https://go.fastrouter.ai/api/v1/responses' \
--header 'Authorization: Bearer API-KEY' \
--header 'Content-Type: application/json' \
--data '{
    "input": [
        {
            "role": "user",
            "content": "Tell me 3 facts about pineapples."
        }
    ],
    "model": "x-ai/grok-4",
    "stream": true
}'

Streaming + Previous Response ID

curl --location 'https://go.fastrouter.ai/api/v1/responses' \
--header 'Authorization: Bearer API-KEY' \
--header 'Content-Type: application/json' \
--data '{
    "input": [
        {
            "role": "user",
            "content": "Tell me one more."
        }
    ],
    "model": "x-ai/grok-4",
    "stream": true,
    "previous_response_id": "fr_123"
}'