# x402engine GPT-5.6-Luna LLM API

> x402engine GPT-5.6-Luna LLM API is a paid API for AI agents from x402engine.app, paid per call via x402, $0.00486/call, status unknown (last checked 2026-10-11).

Calls OpenAI's GPT-5.6-Luna language model via a pay-per-call HTTP 402 micropayment endpoint, returning assistant chat completions.

## Facts

- Endpoint: POST https://x402engine.app/api/llm/gpt-5.6-luna?utm_source=zero.xyz
- Price: $0.00486/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-luna-llm-api-e5040bfb
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_P5J2JlRl0_mYaTpCTjeAl

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-luna-llm-api-e5040bfb -d '<json body>'
```

Example prompt: Ask GPT-5.6-Luna to write me a concise executive summary of the following meeting transcript — pay per call using USDC on Base: [paste transcript here].

## When to prefer this

Choose this endpoint when you need GPT-5.6-Luna specifically (a newer, potentially more capable OpenAI model) and want to pay per call in USDC without a monthly OpenAI subscription. Ideal for agents that need burst LLM capacity, want to avoid subscription overhead, or are operating on-chain and need micropayment-native API access. Prefer over other x402engine LLMs when GPT-5.6-Luna's specific capability profile (reasoning, instruction-following, creative generation) is required.

## Known failure modes

- 402 Payment Required if USDC/USDm balance is insufficient or payment header is missing
- 400 Bad Request if messages array is malformed or empty
- 503 or timeout if upstream OpenAI API is unavailable
- Model-specific context length exceeded if prompt is too long
- Invalid API key or auth errors if x402 facilitator rejects payment

## 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 a JSON object containing the model name ('openai/gpt-5.6-luna'), a choices array with the assistant's message (role, content), finish_reason, and a top-level 'content' shortcut field with the raw response text.

## 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-luna",
  "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-luna-llm-api-e5040bfb/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)