# x402engine GPT-5.2 Pro LLM API

> x402engine GPT-5.2 Pro LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.145674/call, status unknown (last checked 2026-10-12).

Calls OpenAI GPT-5.2 Pro via a pay-per-call HTTP 402 micropayment endpoint, returning an OpenAI-compatible chat completion response

## Facts

- Endpoint: POST https://x402engine.app/api/llm/gpt-5.2-pro?utm_source=zero.xyz
- Price: $0.145674/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402engine-gpt-5-2-pro-llm-api-511c477d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_1es4ryqMwMSuRnEM6D2RY

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-5-2-pro-llm-api-511c477d -d '<json body>'
```

Example prompt: Send this conversation to GPT-5.2 Pro and get a response: system message 'You are a helpful coding assistant', user message 'Write a Python function that parses JSON and handles missing keys gracefully' — pay with USDC on Base.

## When to prefer this

Choose this endpoint when you need access to GPT-5.2 Pro specifically — one of OpenAI's most capable frontier models — without committing to a monthly API subscription. Ideal for AI agents that make sporadic, high-value LLM calls and want to pay per invocation in USDC on Base, USDm on MegaETH, or USDC on Solana. Prefer this over cheaper sibling LLM endpoints when task complexity demands frontier-level reasoning, multi-step tool use, or nuanced instruction following.

## Known failure modes

- Payment not settled — 402 returned if USDC/crypto payment fails or is insufficient
- Invalid message format — 422 if required 'messages' array is missing or malformed
- Tool schema error — model refuses or errors if function definitions are malformed
- Context length exceeded — error if combined message tokens exceed model limit
- Streaming interrupted — SSE stream may drop if network is unstable post-payment

## 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 object containing the model name, an array of choices each with an assistant message (content and optional tool_calls), and a finish_reason (e.g. 'stop'). The top-level 'content' field mirrors the first choice's message content for convenience.

## 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."
      },
      "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."
      },
      "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."
      },
      "messages": {
       "type": "array",
       "items": {
        "type": "object",
        "anyOf": [
         {
          "required": [
           "content"
          ]
         },
         {
          "required": [
           "tool_calls"
          ]
         }
        ],
        "required": [
         "role"
        ],
        "properties": {
         "name": {
          "type": "string"
         },
         "role": {
          "enum": [
           "system",
   
… (truncated)
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "model": "openai/gpt-5.2-pro",
  "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-5-2-pro-llm-api-511c477d/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)