# Model Access Gateway – Claude Sonnet 5.5 via x402

> Model Access Gateway – Claude Sonnet 5.5 via x402 is a paid API for AI agents from agent402-arb.rosariovitale0096.workers.dev, paid per call via x402, $0.0014/call, status unknown (last checked 2026-10-15).

Runs OpenAI-compatible chat completions against Claude Sonnet 5.5, billed per request in USDC on Base using the x402 payment protocol — no account or API key required.

## Facts

- Endpoint: POST https://agent402-arb.rosariovitale0096.workers.dev/llm/claude-sonnet-5.5?utm_source=zero.xyz
- Price: $0.0014/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/model-access-gateway-claude-sonnet-5-5-via-x402-7d72475c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_YtuWrzmmEUoR-H5v62qC-

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-sonnet-5-5-via-x402-7d72475c -d '<json body>'
```

Example prompt: Ask Claude Sonnet 5.5 through the x402 gateway: given the system prompt 'You are a helpful assistant' and the user message 'Summarize the key risks of smart contract audits in 3 bullet points', return the assistant reply and token usage — pay the per-request USDC fee automatically.

## When to prefer this

Choose this endpoint when you need to call Claude Sonnet 5.5 without registering for an Anthropic account or managing API keys, especially in autonomous agent or Web3 contexts where paying per request in USDC on Base (via x402) is preferable to a subscription. It is OpenAI SDK-compatible, so existing code requires minimal changes. Prefer alternatives if you need streaming responses, function calling, vision, or guaranteed SLA.

## Known failure modes

- Insufficient USDC balance causes x402 payment failure and request rejection
- Malformed OpenAI-format body (missing messages array) returns 400 Bad Request
- Model identifier path mismatch returns 404 or model-not-found error
- Rate limiting or Workers concurrency limits may return 429 or 503
- Network timeout on Cloudflare Worker edge may return 524 or 502

## How this service works

Claude Sonnet 5.5 API (anthropic/claude-sonnet-5.5): LLM inference via OpenAI-compatible chat completions, pay per call in USDC on Base with x402. No API key, no account. Suited for AI agents and scripts that need Claude Sonnet 5.5 on demand. When listed, this request cost 30% less than the same request on BlockRun. Streaming and function calling supported. Exact price in the 402 quote before payment; automatic refund if the model fails to answer.

## Output

Returns an OpenAI-compatible chat.completion JSON object containing the assistant's message content, finish reason (e.g. 'stop'), model name ('anthropic/claude-sonnet-5.5'), a unique completion ID, creation timestamp, and token usage breakdown (prompt, completion, total tokens).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "model": {
   "type": "string",
   "description": "Optional: fixed by the route (anthropic/claude-sonnet-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-sonnet-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-sonnet-5-5-via-x402-7d72475c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent402-arb.rosariovitale0096.workers.dev](https://www.zero.xyz/host/agent402-arb.rosariovitale0096.workers.dev/llms.txt)