Name: GPT-4o API: OpenAI Chat Completion with Vision
Brand: magicapi
SKU: api-magicapi-intelligent-chat-api-openai-gpt-4o
Availability: InStock
Author: API Market

Shashank Agarwal

# 💬 Chat Completion API (OpenAI GPT-4o)

## Overview
GPT-4o is a chat model from OpenAI. Its developer describes it as a high-intelligence chat model.

Send either a `prompt` (with an optional `system_prompt`) or a full `messages` list, plus optional `image_input` URLs. The model returns text as a list of chunks; join them in order to get the full response.

## Features
- **Prompt or messages**: send a single `prompt`, or a `messages` list with earlier turns of a conversation. When `messages` is set, `prompt` and `system_prompt` are ignored.
- **System prompt**: set the assistant's behavior with `system_prompt`.
- **Image input**: send a list of image URLs in `image_input`.
- **Sampling controls**: `temperature` (0 to 2, default 1), `top_p` (0 to 1, default 1), `presence_penalty` and `frequency_penalty` (-2 to 2, default 0).
- **Output length**: `max_completion_tokens` (default 4096).

## Use Cases
1. **Chat assistants**: keep a conversation going by sending the history in `messages`.
2. **Question answering**: factual answers and explanations from a short prompt.
3. **Image questions**: describe or compare images sent in `image_input`.
4. **Writing tasks**: drafts, rewrites, summaries and translations.

## Visual Examples
### Example Input
Prompt: "Who was the 16th president of the United States?"

System prompt: "You are a helpful assistant."

Other fields: `image_input` `[]`, `temperature` `1`, `top_p` `1`, `presence_penalty` `0`, `frequency_penalty` `0`, `max_completion_tokens` `4096`.

### Example Output
The output chunks joined into one text:

```text
The 16th president of the United States was Abraham Lincoln. He served from March 4, 1861, until his assassination on April 15, 1865.
```

## Input Parameters
| Field | Type | Required | Default | Allowed values | Description |
| --- | --- | --- | --- | --- | --- |
| `prompt` | string | No | none |  | The prompt to send to the model. Do not use with messages. |
| `system_prompt` | string | No | none |  | System prompt to set the assistant's behavior |
| `messages` | array of objects | No | `[]` |  | List of chat messages, for example [{"role": "user", "content": "Hello, how are you?"}]. If provided, prompt and system_prompt are ignored. |
| `image_input` | array of strings (URLs) | No | `[]` |  | List of images to send to the model |
| `temperature` | number | No | `1` | `0` to `2` | Sampling temperature between 0 and 2 |
| `max_completion_tokens` | integer | No | `4096` |  | Maximum number of completion tokens to generate |
| `top_p` | number | No | `1` | `0` to `1` | Nucleus sampling parameter - the model considers the results of the tokens with top_p probability mass. (0.1 means only the tokens comprising the top 10% probability mass are considered.) |
| `frequency_penalty` | number | No | `0` | `-2` to `2` | Frequency penalty parameter - positive values penalize the repetition of tokens. |
| `presence_penalty` | number | No | `0` | `-2` to `2` | Presence penalty parameter - positive values penalize new tokens based on whether they appear in the text so far, increasing the model's likelihood to talk about new topics. |

## Pricing
- **Pay As You Go (PAYG) pricing**: you only pay for what you use.
- **Price**: $0.0013 per API unit.
- **1 API unit = 100 weighted tokens**; an output token counts 1, an input token counts 0.25.
- That is **$3.25 per million input tokens** and **$13 per million output tokens**.
- Each request rounds up to a whole unit.
- Input tokens include the prompt, the system prompt, the messages and any images.
- **Example cost**: the example request used 29 input tokens and 36 output tokens: 29 x 0.25 + 36 = 43.25 weighted tokens, rounded up to 1 unit, so it cost **$0.0013**.
- **Failed or cancelled predictions are not billed.**
- **GET requests to check prediction status** are free and don't count toward API unit usage.
- **No monthly subscription fee.**

## API Documentation

### Base URL
All API requests go to: `https://prod.api.market/api/v1/magicapi/intelligent-chat-api-openai-gpt-4o`

### Authentication
Send your api.market API key in the `x-api-market-key` header:
```
x-api-market-key: YOUR_API_MARKET_KEY
```

### Asynchronous Processing
**IMPORTANT**: This API is asynchronous. The flow is:
1. Send a POST request to `/predictions`. A successful request returns **201 Created** with a prediction `id` and a `status` of `starting` or `processing`.
2. Poll GET `/predictions/{id}` with that ID.
3. Keep polling while `status` is `starting` or `processing`.
4. Stop when `status` is `succeeded` (read `output`), `failed` or `canceled` (read `error`).

A polling interval of 1 second and an overall timeout of 600 seconds (10 minutes) work well.

### Endpoints

#### Create a Prediction
```bash
curl -X POST "https://prod.api.market/api/v1/magicapi/intelligent-chat-api-openai-gpt-4o/predictions" \
  -H "Content-Type: application/json" \
  -H "x-api-market-key: YOUR_API_MARKET_KEY" \
  -d '{
    "version": "openai/gpt-4o",
    "input": {
      "top_p": 1,
      "prompt": "Who was the 16th president of the United States?",
      "image_input": [],
      "temperature": 1,
      "system_prompt": "You are a helpful assistant.",
      "presence_penalty": 0,
      "frequency_penalty": 0,
      "max_completion_tokens": 4096
    }
  }'
```

Response (201 Created):
```json
{
  "id": "va2cb501r1rmy0d1c6tb2ctdq4",
  "version": "openai/gpt-4o",
  "status": "starting",
  "created_at": "2026-10-22T03:42:29.504Z"
}
```

#### Check Prediction Status
```bash
curl -X GET "https://prod.api.market/api/v1/magicapi/intelligent-chat-api-openai-gpt-4o/predictions/{id}" \
  -H "x-api-market-key: YOUR_API_MARKET_KEY"
```

Response when the prediction has finished (200 OK):
```json
{
  "id": "va2cb501r1rmy0d1c6tb2ctdq4",
  "status": "succeeded",
  "output": [
    "The 16th president of the United States was Abraham Lincoln. He served from March 4, 1861, until his assassination on April 15, 1865."
  ],
  "error": null,
  "created_at": "2026-10-22T03:42:29.504Z",
  "started_at": "2026-10-22T03:42:30.004Z",
  "completed_at": "2026-10-22T03:42:30.907Z"
}
```

`output` is an array of text chunks. Join them in order to get the full response. The example above shows the joined text as one chunk for readability.

### Status Codes
- **201 Created**: prediction created (POST `/predictions`). This is the normal success response.
- **200 OK**: prediction details returned (GET `/predictions/{id}`).
- **400 Bad Request**: invalid input, for example a `temperature` above 2 or a `messages` value that is not a list.
- **401 Unauthorized**: missing or invalid API key.
- **404 Not Found**: no prediction with that ID.
- **429 Too Many Requests**: rate limit exceeded.
- **500 Internal Server Error** or **503 Service Unavailable**: temporary server problem; retry later.

## Rate Limits
All plans allow 10 requests per second. Requests above that return `429 Too Many Requests`; back off before retrying and honour any `Retry-After` header. Polling a prediction with GET is free but still counts toward the per-second limit, so poll every 1 to 5 seconds rather than in a tight loop.

## Error Handling
- Check the HTTP status code of every request and read the response body for the error message.
- A prediction can also end with `status` set to `failed`; the `error` field then explains why. Failed predictions are not billed.
- Retry 429, 500 and 503 responses with exponential backoff. Fix the input before retrying a 400.

## Implementation Guide
### Example Code

#### JavaScript
```javascript
const apiKey = "YOUR_API_MARKET_KEY";
const baseUrl = "https://prod.api.market/api/v1/magicapi/intelligent-chat-api-openai-gpt-4o";

async function createAndWaitForPrediction(input) {
  const response = await fetch(`${baseUrl}/predictions`, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "x-api-market-key": apiKey
    },
    body: JSON.stringify({ version: "openai/gpt-4o", input })
  });

  if (response.status !== 201) {
    throw new Error(`API error: ${response.status} ${await response.text()}`);
  }

  const prediction = await response.json();
  return pollForResults(prediction.id);
}

const delay = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

async function pollForResults(predictionId) {
  const maxTimeout = 600000;
  const pollInterval = 1000;
  const startTime = Date.now();

  while (Date.now() - startTime < maxTimeout) {
    const response = await fetch(`${baseUrl}/predictions/${predictionId}`, {
      headers: { "x-api-market-key": apiKey }
    });

    if (!response.ok) {
      throw new Error(`API error: ${response.status} ${await response.text()}`);
    }

    const prediction = await response.json();

    if (prediction.status === "succeeded") {
      return prediction.output.join("");
    }

    if (prediction.status === "failed" || prediction.status === "canceled") {
      throw new Error(`Prediction ${prediction.status}: ${prediction.error || "Unknown error"}`);
    }

    await delay(pollInterval);
  }

  throw new Error("Prediction timed out after 10 minutes");
}

createAndWaitForPrediction({
    "top_p": 1,
    "prompt": "Who was the 16th president of the United States?",
    "image_input": [],
    "temperature": 1,
    "system_prompt": "You are a helpful assistant.",
    "presence_penalty": 0,
    "frequency_penalty": 0,
    "max_completion_tokens": 4096
  }).then((output) => console.log(output));
```

#### Python
```python
import time
import requests

API_KEY = "YOUR_API_MARKET_KEY"
BASE_URL = "https://prod.api.market/api/v1/magicapi/intelligent-chat-api-openai-gpt-4o"


def create_and_wait_for_prediction(input_data):
    headers = {"Content-Type": "application/json", "x-api-market-key": API_KEY}
    response = requests.post(
        f"{BASE_URL}/predictions",
        headers=headers,
        json={"version": "openai/gpt-4o", "input": input_data},
    )

    if response.status_code != 201:
        raise Exception(f"API error: {response.status_code} {response.text}")

    return poll_for_results(response.json()["id"])


def poll_for_results(prediction_id):
    max_timeout = 600
    poll_interval = 1
    headers = {"x-api-market-key": API_KEY}
    start_time = time.time()

    while time.time() - start_time < max_timeout:
        response = requests.get(f"{BASE_URL}/predictions/{prediction_id}", headers=headers)

        if response.status_code != 200:
            raise Exception(f"API error: {response.status_code} {response.text}")

        prediction = response.json()

        if prediction["status"] == "succeeded":
            return "".join(prediction["output"])

        if prediction["status"] in ("failed", "canceled"):
            raise Exception(f"Prediction {prediction['status']}: {prediction.get('error') or 'Unknown error'}")

        time.sleep(poll_interval)

    raise Exception("Prediction timed out after 10 minutes")


print(create_and_wait_for_prediction({
    "top_p": 1,
    "prompt": "Who was the 16th president of the United States?",
    "image_input": [],
    "temperature": 1,
    "system_prompt": "You are a helpful assistant.",
    "presence_penalty": 0,
    "frequency_penalty": 0,
    "max_completion_tokens": 4096
}))
```

## FAQ
- **How do I get the full answer?**
  - Join the strings in the `output` array in order, for example `output.join("")` in JavaScript or `"".join(output)` in Python.
- **How do I send a multi-turn conversation?**
  - Pass the turns as `messages`, for example `[{"role": "user", "content": "Hello, how are you?"}]`. `prompt` and `system_prompt` are then ignored.
- **Can GPT-4o read images?**
  - Yes. Put one or more image URLs in `image_input`. Images count as input tokens.
- **How do I limit the cost of a request?**
  - Set `max_completion_tokens` lower than the default 4096; output tokens are the larger part of the price.
- **Is the 201 response from POST an error?**
  - No. 201 Created means the prediction was accepted. Use the returned `id` to poll GET `/predictions/{id}` until `status` is `succeeded`, `failed` or `canceled`.
- **What if my prediction fails?**
  - Failed predictions are not billed. Read the `error` field, adjust the input and try again.

## Contact Us
If you have any questions, reach out to us through the chat on the bottom right of the page. You can also email our support team at hello@magicapi.com.


Chat with OpenAI's GPT-4o through a prompt or a message list, with image input, a system prompt and sampling controls. Pay per token, no monthly fee.