# Model Access Gateway – Claude Opus 5.5 Chat Completions (x402, USDC)

> Model Access Gateway – Claude Opus 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 a single Claude Opus 5.5 chat completion request via an OpenAI-compatible API, paid per-call in USDC on Base using x402 — no account or API key required.

## Facts

- Endpoint: POST https://modelaccessgateway.com/llm/claude-opus-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-claude-opus-5-5-chat-completions-x402-usdc-58eb6227
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_vhpkmA-vhlOWsgE7obKks

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-claude-opus-5-5-chat-completions-x402-usdc-58eb6227 -d '<json body>'
```

Example prompt: Ask Claude Opus 5.5 to write me a detailed technical explanation of how transformers work — use the Model Access Gateway pay-per-call endpoint so we don't need an API key, stream the response, and keep it under 2000 tokens.

## When to prefer this

Choose this endpoint when you need Claude Opus 5.5 specifically (Anthropic's most capable model in this gateway) without an Anthropic API account, when operating as an autonomous agent that can settle payments in USDC on Base via x402, or when you want pay-per-call pricing with automatic refunds on failure rather than a monthly subscription. Prefer over direct Anthropic API when no API key management is acceptable, or when building agentic workflows that need trustless, on-chain payment settlement.

## Known failure modes

- Payment failure or insufficient USDC balance — x402 payment rejected, no completion returned but automatic refund triggered
- Model unavailable or overloaded — upstream Anthropic API error, refund issued automatically
- Invalid messages array (empty or malformed) — 400 validation error
- max_tokens exceeds 16384 — 400 schema validation error
- Temperature out of range (0–2) — 400 validation error
- Network timeout during streaming — partial SSE stream, no refund guarantee
- Unsupported role in messages — 400 error referencing enum constraint

## 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, role, finish reason, a unique completion ID, the model name (anthropic/claude-opus-5.5), creation timestamp, and token usage breakdown (prompt, completion, total). When streaming is enabled, responses arrive as server-sent events in the same schema.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "model": {
   "type": "string",
   "description": "Optional: fixed by the route (anthropic/claude-opus-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": "anthropic/claude-opus-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-claude-opus-5-5-chat-completions-x402-usdc-58eb6227/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)