# Model Access Gateway – GPT-5.5 Chat Completions (x402 USDC)

> Model Access Gateway – GPT-5.5 Chat Completions (x402 USDC) is a paid API for AI agents from modelaccessgateway.com, paid per call via x402, $0.0014/call, status unknown (last checked 2026-10-18).

Runs OpenAI GPT-5.5 chat completions via an OpenAI-compatible API, paid per-call in USDC on Base using the x402 protocol — no account or API key required.

## Facts

- Endpoint: POST https://modelaccessgateway.com/llm/gpt-5.5?utm_source=zero.xyz
- Price: $0.0014/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-18
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/model-access-gateway-gpt-5-5-chat-completions-x402-usdc-46135043
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_VzI6hWbO2U0daFq7hPYjK

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 model-access-gateway-gpt-5-5-chat-completions-x402-usdc-46135043 -d '<json body>'
```

Example prompt: Ask GPT-5.5 to write a professional summary for a software engineer with 10 years of Python experience — pay per call in USDC, no API key needed, and keep the response under 300 tokens.

## When to prefer this

Choose this endpoint when you need GPT-5.5 specifically, want OpenAI-compatible chat completions without managing an OpenAI account or API key, and can pay per-call in USDC via the x402 protocol. Ideal for autonomous AI agents that need anonymous, accountless LLM access with built-in payment and automatic refund on failure. Prefer this over direct OpenAI when operating in a crypto-native or x402-enabled environment.

## Known failure modes

- Model failure triggers automatic USDC refund — agent receives error response and payment is returned
- Insufficient USDC balance causes x402 payment rejection before inference begins
- Invalid or missing messages array returns a 400-level validation error
- max_tokens exceeding 16384 is rejected at schema validation
- Streaming requested but client doesn't handle SSE — incomplete response received

## How this service works

LLM inference API: OpenAI-compatible chat completions for 136 AI models (Claude, GPT, Gemini, Grok, DeepSeek, Qwen, Kimi, GLM), paid per call in USDC on Base with x402. No account, no API key, automatic refund if the model fails.

## Output

Returns an OpenAI-compatible chat.completion JSON object containing the assistant's message content, finish reason, model used, and token usage (prompt, completion, total). On streaming, delivers server-sent events. If the model fails, an automatic USDC refund is issued.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "model": {
   "type": "string",
   "description": "Optional: fixed by the route (openai/gpt-5.5)"
  },
  "tools": {
   "type": "array"
  },
  "stream": {
   "type": "boolean",
   "description": "true: server-sent events after payment"
  },
  "messages": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "role"
    ],
    "properties": {
     "role": {
      "enum": [
       "system",
       "user",
       "assistant",
       "tool",
       "developer"
      ],
      "type": "string"
     },
     "content": {
      "type": [
       "string",
       "array",
       "null"
      ]
     }
    }
   },
   "minItems": 1
  },
  "max_tokens": {
   "type": "integer",
   "maximum": 16384,
   "minimum": 1,
   "description": "Optional, default 4096"
  },
  "temperature": {
   "type": "number",
   "maximum": 2,
   "minimum": 0
  },
  "response_format": {
   "type": "object"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "id": "chatcmpl-7f3c2a91",
  "model": "openai/gpt-5.5",
  "usage": {
   "total_tokens": 10,
   "prompt_tokens": 9,
   "completion_tokens": 1
  },
  "object": "chat.completion",
  "choices": [
   {
    "index": 0,
    "message": {
     "role": "assistant",
     "content": "OK"
    },
    "finish_reason": "stop"
   }
  ],
  "created": 1791979200
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/model-access-gateway-gpt-5-5-chat-completions-x402-usdc-46135043/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from modelaccessgateway.com](https://www.zero.xyz/host/modelaccessgateway.com/llms.txt)