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x402engine GPT-5.1 LLM API
x402
x402engine GPT-5.1 LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.010015/call, status unknown (last checked 2026-10-12).
Calls OpenAI's GPT-5.1 model via a pay-per-call HTTP 402 micropayment endpoint, returning OpenAI-compatible chat completions
Price / call$0.010015
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 object containing the model name (openai/gpt-5.1), a choices array with the assistant message (role, content, tool_calls if any), and a finish_reason. Also exposes a top-level content shortcut field. Supports SSE streaming when stream=true.
Example use cases
Agent reasoning with tool use
“Use GPT-5.1 to decide which of my three Python functions to call next based on this conversation history — pass the function definitions as tools and let it pick one.”
Multimodal image analysis
“Send this product photo and my system prompt to GPT-5.1 and ask it to write a two-sentence marketing blurb based on what it sees in the image.”
Streaming customer support reply
“Have GPT-5.1 draft a polite response to this customer complaint, streaming the answer live as it generates — here are the last five messages in the thread as context.”
Technical details
Endpoint
POSThttps://x402engine.app/api/llm/gpt-5.1?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need GPT-5.1 specifically (OpenAI's latest flagship model) and want pay-per-call pricing with no API key management, billed in USDC on Base, USDm on MegaETH, or USDC on Solana. Ideal for autonomous agents, serverless pipelines, or situations where you want to avoid OpenAI subscription overhead. Prefer alternatives if you need a cheaper model for high-volume simple tasks (use Claude Haiku or MiMo-Flash siblings), need video or image generation (use Kling/FLUX siblings), or need audio transcription.
Side effects
- Payment not settled — 402 returned if USDC/USDm balance is insufficient
- Invalid messages array — 400 if required role or content fields are missing
- Token limit exceeded — model returns an error or truncated finish_reason
- Tool call schema mismatch — malformed function definitions cause 400 or unexpected behavior
- Streaming timeout — SSE connection dropped on slow clients
- Unsupported seed value — model may ignore or error on out-of-range seeds
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"model": "openai/gpt-5.1",
"choices": [
{
"index": 0,
"message": {
"role": "assistant",
"content": "Hello!"
},
"finish_reason": "stop"
}
],
"content": "Hello!"
}
}Tags
x402
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