# GPT-4o via x402 Gateway

> GPT-4o via x402 Gateway is a paid API for AI agents from x402-gateway-production.up.railway.app, paid per call via x402, $0.040000/call, status unknown (last checked 2026-10-12, last successful call 2026-04-16).

Calls OpenAI's GPT-4o multimodal model (text, vision, reasoning) through a pay-per-call x402 gateway at $0.04 USDC

## Facts

- Endpoint: POST https://x402-gateway-production.up.railway.app/api/llm/gpt-4o?utm_source=zero.xyz
- Price: $0.040000/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Last successful call: 2026-04-16
- Success rate: 20% of calls made through Zero
- Activations on Zero: 5
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-gateway-production-up-railway-app-97809b5a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_WI5jPqbpzpEOyCdG7j4Xc

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability x402-gateway-production-up-railway-app-97809b5a -d '<json body>'
```

Example prompt: Use GPT-4o to analyze this product screenshot and write me a concise summary of its key features — the image is at https://example.com/product.png and I want a 3-bullet summary in plain English.

## When to prefer this

Choose this endpoint when you need OpenAI's best all-around model (GPT-4o) with multimodal capability (text + vision) and you want pay-per-call access via x402 without managing OpenAI API keys or subscriptions. Prefer over Claude or DeepSeek siblings when OpenAI-specific output quality, tool compatibility, or vision reasoning is required.

## Known failure modes

- Payment not included or insufficient USDC balance — returns 402 Payment Required
- Invalid or malformed prompt body — returns 400 Bad Request
- OpenAI upstream timeout or rate limit — returns 503 or 504
- Unsupported image format or inaccessible image URL — model may ignore image or return error
- Gateway downtime on Railway — returns 502 or 503

## How this service works

OpenAI's flagship multimodal model — strong all-around for text, vision, and reasoning

## Output

Returns a natural language completion from GPT-4o — text response, analysis output, or reasoning result based on the provided prompt and any attached images.

## Example request

```json
{
 "model": "gpt-4o",
 "messages": [
  {
   "role": "user",
   "content": "Analyze the following image and provide a 3-bullet summary of key features: https://example.com/product.png"
  }
 ],
 "max_tokens": 150
}
```

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "bodyType",
    "body",
    "method"
   ],
   "properties": {
    "body": {
     "type": "object",
     "required": [
      "messages"
     ],
     "properties": {
      "seed": {
       "type": "integer",
       "description": "Model-supported seed; see /docs/llm-capabilities.md."
      },
      "stop": {
       "oneOf": [
        {
         "type": "string"
        },
        {
         "type": "array",
         "items": {
          "type": "string"
         },
         "maxItems": 4
        }
       ],
       "description": "Model-supported stop; see /docs/llm-capabilities.md."
      },
      "tools": {
       "type": "array",
       "items": {
        "type": "object",
        "required": [
         "function"
        ],
        "properties": {
         "type": {
          "enum": [
           "function"
          ],
          "type": "string"
         },
         "function": {
          "type": "object",
          "properties": {
           "name": {
            "type": "string"
           },
           "strict": {
            "type": "boolean"
           },
           "parameters": {
            "type": "object"
           },
           "description": {
            "type": "string"
           }
          }
         }
        }
       },
       "description": "Client-executed function definitions; return results using role=tool and tool_call_id."
      },
      "top_p": {
       "type": "number",
       "description": "Model-supported top_p; see /docs/llm-capabilities.md."
      },
      "stream": {
       "type": "boolean",
       "description": "Return live OpenAI-compatible SSE after payment settlement."
      },
      "plugins": {
       "type": "array",
       "items": {
        "type": "object",
        "required": [
         "pdf"
        ],
        "properties": {
         "id": {
          "enum": [
           "file-parser"
          ],
          "type": "string"
         },
         "pdf": {
          "type": "object",
          "properties": {
           "engine": {
            "enum": [
             "native"
            ],
            "type": "string"
           }
          }
         }
        }
       },
       "description": "Optional native PDF parser only; automatically enabled for file inputs."
      },
      "logprobs": {
       "type": "bool
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-gateway-production-up-railway-app-97809b5a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402-gateway-production.up.railway.app](https://www.zero.xyz/host/x402-gateway-production.up.railway.app/llms.txt)