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x402engine GPT-4o LLM API
x402
x402engine GPT-4o LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.018586/call, status unknown (last checked 2026-10-12).
Calls OpenAI GPT-4o via HTTP 402 micropayment, returning an OpenAI-compatible chat completion response for a given message array.
Price / call$0.018586
Success—
StatusUnknown
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
Returns an OpenAI-compatible JSON chat completion object containing the model name, an array of choices with the assistant's message content and finish reason, and a top-level 'content' shortcut field. When streaming is enabled, delivers OpenAI-compatible server-sent events (SSE) incrementally.
Example use cases
Agent reasoning with tool calling
“Send this conversation history to GPT-4o with my search_web and run_code tool definitions attached, and return whatever tool calls or final answer it produces — I'm building an autonomous research agent.”
Multimodal document Q&A
“Pass this PDF invoice to GPT-4o and ask it to extract the vendor name, total amount due, and payment deadline, then return the result as structured JSON.”
Crypto-native app LLM backend
“I need GPT-4o to answer a user's question about DeFi yield strategies — send their message with a system prompt saying 'You are a helpful DeFi advisor' and pay for the call with USDC on Base.”
Technical details
Endpoint
POSThttps://x402engine.app/api/llm/gpt-4o?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need GPT-4o specifically (not a generic LLM), want to pay per-call in USDC without an OpenAI subscription, are building a crypto-native or agent-to-agent workflow that benefits from HTTP 402 micropayments, or need OpenAI-compatible streaming and tool/function calling without managing API keys.
Side effects
- Payment not settled — 402 response if USDC funds are insufficient
- Invalid messages array — 400 if required 'messages' field is missing or malformed
- Unsupported parameter for model — some optional fields (seed, logprobs, top_p) may not be supported by all model variants
- Streaming not supported in some client environments — SSE requires persistent HTTP connection
- Tool call format errors — malformed function definitions will cause 400 or unexpected behavior
- Rate limiting or upstream OpenAI outage — may return 503 or timeout
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"model": "openai/gpt-4o",
"choices": [
{
"index": 0,
"message": {
"role": "assistant",
"content": "Hello!"
},
"finish_reason": "stop"
}
],
"content": "Hello!"
}
}Tags
x402
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