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

> OpenAI GPT-5.6 Luna Chat Completions (x402, USDC) is a paid API for AI agents from openai.mm.family, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-03).

Runs chat completions against the GPT-5.6-Luna model (up to 272K input tokens) with pay-per-call billing in USDC via the x402 protocol.

## Facts

- Endpoint: POST https://openai.mm.family/x402/v1/models/gpt-5.6-luna/chat/completions?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-03
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/openai-gpt-5-6-luna-chat-completions-x402-usdc-c554fa8d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_xwDAxu1rokohcm0ZBeQWD

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 openai-gpt-5-6-luna-chat-completions-x402-usdc-c554fa8d -d '<json body>'
```

Example prompt: Send this conversation to GPT-5.6 Luna with medium reasoning level and flex pricing: system: 'You are a concise assistant', user: 'Explain quantum entanglement in two sentences', and give me back the assistant reply.

## When to prefer this

Choose this endpoint when you need GPT-5.6 Luna specifically, want pay-per-call USDC billing without an OpenAI subscription, need to tune reasoning depth via model suffix levels (none through xhigh), or are building agents on the x402 payment protocol. Prefer over o3 or o4-mini when you want a balance of reasoning quality and cost (Flex at $0.10/$0.60 per 1M tokens). Use gpt-5.5-long or gpt-6-sol-long siblings for inputs exceeding 272K tokens.

## Known failure modes

- 402 Payment Required — insufficient USDC balance or x402 payment header missing/invalid
- 400 Bad Request — invalid model name, unsupported service_tier, or malformed messages array
- context length exceeded — input tokens surpass the 272K limit for this model variant
- rate limiting — too many concurrent requests at the chosen service tier
- empty completion returned — model produced no output (billed $0 but no useful result)
- timeout — fast/flex tier may deprioritize requests under load causing delayed or dropped responses

## How this service works

gpt-5.6-luna: OpenAI GPT 5.6 Luna (<=272K input tokens) chat completions, paid per call in USDC. Per 1M tokens in/out: Flex (default) 0.1/0.6, Standard 0.2/1.2, Fast 0.4/2.4; pick with service_tier. Plus $0.0005 (Base) or $0.0005 (Solana) per call; the quote charges input plus 10% of max_tokens. Levels: none, low, medium, high, xhigh (model gpt-5.6-luna:<level>). Empty answers are free. Rates: https://openai.mm.family/x402/pricing

## Output

Returns a standard OpenAI chat.completion JSON object containing the assistant's message content, finish_reason (stop/tool_calls/length), prompt and completion token counts, the service_tier used, and a unique completion ID. Empty responses (when the model produces no content) are billed at $0.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "model": {
   "enum": [
    "gpt-5.6-luna",
    "gpt-5.6-luna:none",
    "gpt-5.6-luna:low",
    "gpt-5.6-luna:medium",
    "gpt-5.6-luna:high",
    "gpt-5.6-luna:xhigh"
   ],
   "type": "string"
  },
  "tools": {
   "type": "array"
  },
  "stream": {
   "type": "boolean"
  },
  "messages": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "role",
     "content"
    ],
    "properties": {
     "role": {
      "type": "string"
     },
     "content": {
      "type": "string"
     }
    }
   }
  },
  "max_tokens": {
   "type": "integer"
  },
  "service_tier": {
   "enum": [
    "flex",
    "default",
    "standard",
    "auto",
    "fast",
    "priority"
   ],
   "type": "string"
  },
  "response_format": {
   "type": "object"
  },
  "reasoning_effort": {
   "type": "string"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "id": "chatcmpl-x",
  "model": "gpt-5.6-luna",
  "usage": {
   "total_tokens": 9,
   "prompt_tokens": 8,
   "completion_tokens": 1
  },
  "object": "chat.completion",
  "choices": [
   {
    "index": 0,
    "message": {
     "role": "assistant",
     "content": "Hello",
     "refusal": null
    },
    "finish_reason": "stop"
   }
  ],
  "service_tier": "flex"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/openai-gpt-5-6-luna-chat-completions-x402-usdc-c554fa8d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from openai.mm.family](https://www.zero.xyz/host/openai.mm.family/llms.txt)