# x402engine GPT-5 Nano LLM API

> x402engine GPT-5 Nano LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.001773/call, status unknown (last checked 2026-10-12).

Runs OpenAI GPT-5 Nano chat completions via pay-per-call HTTP 402 micropayment, returning an OpenAI-compatible response

## Facts

- Endpoint: POST https://x402engine.app/api/llm/gpt-5-nano?utm_source=zero.xyz
- Price: $0.001773/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-nano-llm-api-a1f97776
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_lggA4sJM-IsRc1y1c9QS7

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-nano-llm-api-a1f97776 -d '<json body>'
```

Example prompt: Send this conversation to GPT-5 Nano and get a reply: system message is 'You are a helpful assistant', user message is 'What is the capital of France?' — pay per call with USDC on Base.

## When to prefer this

Choose this endpoint when you need a cheap, fast OpenAI-compatible chat completion (GPT-5 Nano) and want to pay per call in USDC on Base without an OpenAI subscription. Ideal for AI agent pipelines that need cost-controlled LLM inference with tool calling and streaming support, especially when the agent already handles x402 micropayment headers.

## Known failure modes

- 402 Payment Required if USDC balance is insufficient or payment settlement fails
- 400 Bad Request if messages array is missing or malformed
- Model-level refusal if content policy is triggered (finish_reason=content_filter)
- Timeout or partial stream if network drops mid-SSE stream
- Invalid tool definition schema causes tool_calls to fail silently

## 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 with a choices array containing the assistant message, finish_reason ('stop', 'tool_calls', etc.), and model name ('openai/gpt-5-nano'). Optionally streams SSE tokens if stream=true.

## 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-nano",
  "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-nano-llm-api-a1f97776/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)