# x402engine GPT-5.6 LLM API

> x402engine GPT-5.6 LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.035735/call, status unknown (last checked 2026-10-11).

Provides pay-per-call access to OpenAI's GPT-5.6 model for complex analysis, coding, and planning tasks via HTTP 402 micropayments

## Facts

- Endpoint: POST https://x402engine.app/api/llm/gpt-5.6-sol?utm_source=zero.xyz
- Price: $0.035735/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402engine-gpt-5-6-llm-api-ed9828b1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_W6CbjPOocN8YYEv7l0DFV

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-5-6-llm-api-ed9828b1 -d '<json body>'
```

Example prompt: Use the x402engine GPT-5.6 endpoint to analyze this codebase for security vulnerabilities and produce a prioritized list of issues with recommended fixes — pay the $0.08 USDC fee per call.

## When to prefer this

Choose this endpoint when you need OpenAI's GPT-5.6 capability for complex, multi-step reasoning, advanced coding, or detailed planning without setting up a full OpenAI account or subscription. It is ideal for AI agents that need to make occasional high-quality LLM calls and pay per use in USDC via the x402 micropayment protocol, avoiding upfront commitments or API key management overhead.

## Known failure modes

- Insufficient USDC balance causes HTTP 402 payment failure
- Malformed request body or missing required fields returns a 400 error
- Model overload or rate limiting may cause 429 or 503 responses
- Overly long prompts exceeding context window limits return an error
- Network timeouts on very long generations

## How this service works

OpenAI's flagship GPT-5.6 tier for complex analysis, coding, and planning

## Output

Returns a generated text completion from GPT-5.6, which may include prose, code, structured analysis, or a step-by-step plan depending on the prompt. The response follows standard LLM chat completion format with the model's output message.

## 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-5.6-sol",
  "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-5-6-llm-api-ed9828b1/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)