# GPT-5.6 Luna Chat Completions (x402, OpenAI-Compatible)

> GPT-5.6 Luna Chat Completions (x402, OpenAI-Compatible) is a paid API for AI agents from gpt55.558686.xyz, paid per call via x402, $0.019999/call, status unknown (last checked 2026-10-11).

Returns an OpenAI-compatible chat completion from the GPT-5.6 Luna model via a pay-per-call GET request priced in USDC over x402.

## Facts

- Endpoint: GET https://gpt55.558686.xyz/v1/chat/completions/gpt-5.6-luna?utm_source=zero.xyz
- Price: $0.019999/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/gpt-5-6-luna-chat-completions-x402-openai-compatible-c2b40b33
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_HYUKAoRA6PjJJ-t23ZDuk

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 gpt-5-6-luna-chat-completions-x402-openai-compatible-c2b40b33
```

Example prompt: Using the GPT-5.6 Luna model, answer this question with up to 200 tokens: 'What are three concise tips for reducing cloud infrastructure costs?' — use the system prompt 'You are a helpful cloud cost advisor.'

## When to prefer this

Choose this endpoint when you need a pay-per-call, no-subscription LLM inference endpoint that accepts USDC micropayments via x402 and is OpenAI API-compatible, especially if your agent wallet supports x402 payment flows. It is well-suited for lightweight routing, extraction, short QA, and buyer triage tasks where per-request billing is preferred over a monthly API key subscription. Prefer alternatives (e.g. direct OpenAI API) when you need guaranteed model provenance, SLA, or longer context reliability.

## Known failure modes

- Payment not included or insufficient USDC causes 402 Payment Required with a payment challenge
- Invalid or missing 'model' query parameter returns an error or falls back to default model
- Prompt or message too long exceeds max_tokens limit of 128000
- GET method limitations mean very long prompts may be truncated by URL length restrictions
- Unknown or unsupported model enum value causes rejection
- Rate limiting or quota exceeded on the upstream provider returns 429
- Domain or infrastructure outage on 558686.xyz returns 5xx

## How this service works

GPT-5.6 Luna API Base USDC and OpenAI-compatible x402 chat: one request for $0.00293, paid by browser wallet or a quote-first agent fallback.

## Output

A JSON object in OpenAI chat.completion format containing: a unique completion ID, the model name ('gpt-5.6-luna'), an array of choices each with an assistant message and finish_reason, and a usage object with prompt_tokens, completion_tokens, and total_tokens.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "pathParams": {
     "type": "object",
     "additionalProperties": true
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "q": {
       "type": "string"
      },
      "input": {
       "type": "string"
      },
      "model": {
       "enum": [
        "gpt-5.6-sol",
        "gpt-5.6",
        "gpt-5.6-luna",
        "gpt-5.6-terra",
        "gpt-5.5",
        "gpt-5.3-codex",
        "gpt-5.4"
       ],
       "type": "string"
      },
      "prompt": {
       "type": "string"
      },
      "system": {
       "type": "string"
      },
      "message": {
       "type": "string"
      },
      "max_tokens": {
       "type": "integer",
       "maximum": 128000,
       "minimum": 1
      },
      "system_prompt": {
       "type": "string"
      },
      "max_output_tokens": {
       "type": "integer",
       "maximum": 128000,
       "minimum": 1
      }
     },
     "additionalProperties": true
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "id",
      "object",
      "model",
      "choices"
     ],
     "properties": {
      "id": {
       "type": "string"
      },
      "model": {
       "type": "string"
      },
      "usage": {
       "type": "object"
      },
      "object": {
       "type": "string"
      },
      "choices": {
       "type": "array"
      }
     },
     "additionalProperties": true
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "id": "chatcmpl_example",
  "model": "gpt-5.6-luna",
  "usage": {
   "total_tokens": 44,
   "prompt_tokens": 32,
   "completion_tokens": 12
  },
  "object": "chat.completion",
  "choices": [
   {
    "index": 0,
    "message": {
     "role": "assistant",
     "content": "A concise answer from GPT-5.5."
    },
    "finish_reason": "stop"
   }
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/gpt-5-6-luna-chat-completions-x402-openai-compatible-c2b40b33/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from gpt55.558686.xyz](https://www.zero.xyz/host/gpt55.558686.xyz/llms.txt)