# GPT-5.5 x402 Chat Completions Gateway

> GPT-5.5 x402 Chat Completions Gateway is a paid API for AI agents from gpt55.558686.xyz, paid per call via x402, $0.00293/call, down (last probed 2026-10-12); live alternatives: agent402.tools LLM Inference Proxy ($0.01) and Bankr LLM Gateway (free).

Agents call it through Zero, which pays per call: no API key and no wallet of your own. New accounts start with $5.

Live alternatives for the same use case:
- [agent402.tools LLM Inference Proxy](https://www.zero.xyz/c/agent402-tools-llm-inference-proxy-gpt-4o-mini-0d820d98) ($0.01)
- [Bankr LLM Gateway](https://www.zero.xyz/c/bankr-4f042050) (free)

Provides OpenAI-compatible GPT-5.5 chat completions via a pay-per-call GET endpoint using x402 USDC micropayments on Base

## Facts

- Endpoint: GET https://gpt55.558686.xyz/v1/chat/completions?utm_source=zero.xyz
- Price: $0.00293/call
- Payment: x402
- Status: down
- Last checked: 2026-10-12
- Last successful call: 2026-07-11
- Success rate: 50% of calls made through Zero
- Rating: 5.0 / 5 from 1 review
- Activations on Zero: 2
- Tags: x402
- Canonical page: https://www.zero.xyz/c/gpt-5-5-x402-chat-completions-gateway-7569a68c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_t3vUTZRUibtn9b-EahQKm

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 gpt-5-5-x402-chat-completions-gateway-7569a68c
```

Example prompt: Ask GPT-5.5 via the x402 micropayment gateway: using gpt-5.5 model with a system prompt of 'You are a helpful assistant' and up to 150 output tokens, answer this question — what are the three laws of thermodynamics?

## When to prefer this

Choose this endpoint when you need GPT-5.5 chat completions on a true pay-per-call basis with no subscription, especially in agentic or automated pipelines that use x402 USDC micropayments on Base. Ideal for low-volume or sporadic usage where a $0.0001 per call cost is acceptable and no OpenAI account is required. Prefer over direct OpenAI API when you want crypto-native payment rails.

## Known failure modes

- Payment not included or insufficient USDC via x402 — returns 402 Payment Required
- max_tokens exceeds 192 — rejected by schema validation
- Missing required input/prompt parameter — returns error or empty response
- Model enum value other than 'gpt-5.5' not accepted
- Rate limiting or upstream OpenAI API failure — service unavailable

## How this service works

Low-cost OpenAI-compatible GPT-5.5 chat completion for AI agents, apps, and scripts. Pay up to $0.004 per request with x402 USDC on Base. Exact fixed-price and upto usage-based payment are both accepted when clients support them. Public paid calls are limited to 1500 input characters and 128 output tokens for predictable cost.

## Output

Returns an OpenAI-compatible chat.completion JSON object containing the assistant's text reply, model name, a unique completion ID, finish reason (e.g. 'stop'), and token usage stats (prompt tokens, completion tokens, total tokens).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "pathParams": {
     "type": "object",
     "additionalProperties": true
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "q": {
       "type": "string"
      },
      "input": {
       "type": "string"
      },
      "model": {
       "enum": [
        "gpt-5.6-sol",
        "gpt-5.6",
        "gpt-5.6-terra",
        "gpt-5.5"
       ],
       "type": "string"
      },
      "prompt": {
       "type": "string"
      },
      "system": {
       "type": "string"
      },
      "message": {
       "type": "string"
      },
      "max_tokens": {
       "type": "integer",
       "maximum": 128000,
       "minimum": 1
      },
      "system_prompt": {
       "type": "string"
      },
      "max_output_tokens": {
       "type": "integer",
       "maximum": 128000,
       "minimum": 1
      }
     },
     "additionalProperties": true
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "id",
      "object",
      "model",
      "choices"
     ],
     "properties": {
      "id": {
       "type": "string"
      },
      "model": {
       "type": "string"
      },
      "usage": {
       "type": "object"
      },
      "object": {
       "type": "string"
      },
      "choices": {
       "type": "array"
      }
     },
     "additionalProperties": true
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "id": "chatcmpl_example",
  "model": "gpt-5.5",
  "usage": {
   "total_tokens": 44,
   "prompt_tokens": 32,
   "completion_tokens": 12
  },
  "object": "chat.completion",
  "choices": [
   {
    "index": 0,
    "message": {
     "role": "assistant",
     "content": "A concise answer from GPT-5.5."
    },
    "finish_reason": "stop"
   }
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/gpt-5-5-x402-chat-completions-gateway-7569a68c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from gpt55.558686.xyz](https://www.zero.xyz/host/gpt55.558686.xyz/llms.txt)