# x402engine GPT-4o Mini LLM API

> x402engine GPT-4o Mini LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.002458/call, status unknown (last checked 2026-10-11).

Runs OpenAI GPT-4o Mini inference via pay-per-call HTTP 402 micropayment, returning OpenAI-compatible chat completions

## Facts

- Endpoint: POST https://x402engine.app/api/llm/gpt-4o-mini?utm_source=zero.xyz
- Price: $0.002458/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402engine-gpt-4o-mini-llm-api-f326353e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_MaUH08n51VRA7hcQHatZI

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 x402engine-gpt-4o-mini-llm-api-f326353e -d '<json body>'
```

Example prompt: Ask GPT-4o Mini: given this customer email, draft a polite two-sentence reply acknowledging their complaint and promising follow-up within 24 hours — stream the response back to me.

## When to prefer this

Choose this endpoint when you need OpenAI GPT-4o Mini inference on a pay-per-call basis without managing an OpenAI API key or monthly subscription — ideal for AI agents that must pay autonomously using USDC on Base, USDm on MegaETH, or USDC on Solana. Prefer this over direct OpenAI access when your agent runtime supports HTTP 402 micropayments, when call volume is unpredictable, or when you want crypto-native billing. It is a drop-in OpenAI-compatible interface so migration is minimal.

## Known failure modes

- Payment not settled — 402 returned if USDC balance is insufficient or payment header is missing
- Unsupported parameter — if a capability like logprobs or seed is not supported by gpt-4o-mini, the field is silently ignored or returns an error per docs
- Malformed messages array — missing required 'role' or neither 'content' nor 'tool_calls' causes a 400 validation error
- Rate limits — upstream OpenAI throttling may cause 429 or delayed responses
- Streaming failure — SSE stream may drop if network is unstable after payment settlement

## How this service works

125 production APIs behind HTTP 402 micropayments. 87 LLMs, Kling V3 and Hailuo video generation, image generation, code execution, travel search, web scraping, TTS, and transaction simulation. Pay with USDC on Base, USDm on MegaETH, or USDC on Solana.

## Output

An OpenAI-compatible JSON response containing the model name, an array of choices each with a role='assistant' message and finish_reason, and a top-level 'content' shortcut field. Supports streaming SSE if stream=true is set.

## 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)
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "model": "openai/gpt-4o-mini",
  "choices": [
   {
    "index": 0,
    "message": {
     "role": "assistant",
     "content": "Hello!"
    },
    "finish_reason": "stop"
   }
  ],
  "content": "Hello!"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402engine-gpt-4o-mini-llm-api-f326353e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402engine.app](https://www.zero.xyz/host/x402engine.app/llms.txt)