# OpenAI GPT-5.5 Chat Completions (x402/USDC)

> OpenAI GPT-5.5 Chat Completions (x402/USDC) is a paid API for AI agents from openai.mm.family, paid per call via x402, $0.001284/call, status unknown (last checked 2026-10-02).

Runs GPT-5.5 chat completions with up to 272K input tokens, billed per call in USDC via the x402 protocol with configurable service tiers.

## Facts

- Endpoint: POST https://openai.mm.family/x402/v1/models/gpt-5.5/chat/completions?utm_source=zero.xyz
- Price: $0.001284/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/openai-gpt-5-5-chat-completions-x402-usdc-d842ef21
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_PQo0UOfTY2M8TOyqzZIar

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-5-5-chat-completions-x402-usdc-d842ef21 -d '<json body>'
```

Example prompt: Using GPT-5.5 on the openai.mm.family x402 gateway, send this conversation — system: 'You are a helpful assistant', user: 'Explain quantum entanglement in two sentences' — with standard service tier, max 200 tokens, and pay per call in USDC.

## When to prefer this

Choose this endpoint when you need GPT-5.5 specifically (not gpt-4o or gpt-5-mini), want to pay per call in USDC via x402 micropayments without a traditional OpenAI API key subscription, need up to 272K input context (use the long-context sibling for more), or want to control cost-vs-latency tradeoffs via service_tier (flex for cheapest, fast for lowest latency). Prefer over sibling models when GPT-5.5 capability level is the target and the context fits within 272K tokens.

## Known failure modes

- Insufficient USDC balance causes payment failure before completion
- Context length exceeds 272K tokens — use the long-context sibling endpoint instead
- Invalid service_tier value causes request rejection
- max_tokens set too high leads to over-quoted charges
- Model variant string not in allowed enum causes 422 error
- Streaming mode (stream:true) may require special client handling

## How this service works

gpt-5.5: OpenAI GPT 5.5 (<=272K input tokens) chat completions, paid per call in USDC. Per 1M tokens in/out: Flex (default) 2.5/15.0, Standard 5.0/30.0, Fast 12.5/75.0; 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-5.5:<level>). Empty answers are free. Rates: https://openai.mm.family/x402/pricing

## Output

Returns a JSON chat completion object containing the assistant's message text, the model used, finish reason (e.g. 'stop'), token counts (prompt, completion, total), the service tier applied, and a unique completion ID. Empty completions are returned free of charge.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "model": {
   "enum": [
    "gpt-5.5",
    "gpt-5.5:none",
    "gpt-5.5:low",
    "gpt-5.5:medium",
    "gpt-5.5:high",
    "gpt-5.5: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-5.5",
  "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-5-5-chat-completions-x402-usdc-d842ef21/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)