# x402engine GPT-5.4 LLM API

> x402engine GPT-5.4 LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.035747/call, status unknown (last checked 2026-10-16).

Calls OpenAI GPT-5.4 via HTTP 402 micropayment, returning an OpenAI-compatible chat completion response

## Facts

- Endpoint: POST https://x402engine.app/api/llm/gpt-5.4?utm_source=zero.xyz
- Price: $0.035747/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402engine-gpt-5-4-llm-api-fd5458ca
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_RcfWfhrkUdz5URyNm42GB

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-5-4-llm-api-fd5458ca -d '<json body>'
```

Example prompt: Send this conversation to GPT-5.4 and get a response: system prompt is 'You are a helpful coding assistant', user message is 'Write a Python function that parses JSON and handles errors gracefully' — stream the reply back to me.

## When to prefer this

Choose this endpoint when you need GPT-5.4 specifically (the latest OpenAI flagship model) on a pay-per-call basis without a monthly OpenAI subscription, especially in agentic pipelines that pay with USDC on Base, USDm on MegaETH, or USDC on Solana. Prefer it over other x402engine LLMs when you need OpenAI's most capable reasoning, tool use, and instruction-following. It is well-suited for agents that make infrequent or variable-volume calls and want to avoid subscription overhead.

## Known failure modes

- Payment not settled — 402 response if USDC/USDm balance is insufficient
- Invalid messages array — missing required 'role' or 'content'/'tool_calls' field causes schema validation error
- Tool call schema malformed — function definition missing 'function' key
- Unsupported seed value — model may not honor seed if capability is not listed in /docs/llm-capabilities.md
- Rate limit or upstream OpenAI outage — proxied 5xx errors from underlying provider
- Stream requested but SSE not handled — client must support chunked transfer encoding

## How this service works

x402engine — OpenAI's unified flagship model — 1M context, computer use, top-tier across all tasks

## Output

Returns an OpenAI-compatible JSON chat completion object including the model name ('openai/gpt-5.4'), a choices array with the assistant message content, role, and finish_reason ('stop', 'tool_calls', etc.), plus a top-level 'content' field with the response text. Streaming mode returns OpenAI-compatible SSE events.

## 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-5.4",
  "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-5-4-llm-api-fd5458ca/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)