# FarOut LLM Gateway – Pay-Per-Call Chat Completions (GPT-5.5)

> FarOut LLM Gateway – Pay-Per-Call Chat Completions (GPT-5.5) is a paid API for AI agents from farouter.tech, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-13).

Runs a chat completion request against GPT-5.5 (or any supported frontier model) with per-call USDC micropayment via x402 — no API key or account required.

## Facts

- Endpoint: POST https://farouter.tech/v1/models/gpt-5.5/chat/completions
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/farout-llm-gateway-pay-per-call-chat-completions-gpt-5-5-48b89a9c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Uw5fQqpit5KmLoPpIJc_N

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 farout-llm-gateway-pay-per-call-chat-completions-gpt-5-5-48b89a9c -d '<json body>'
```

Example prompt: Ask GPT-5.5 via FarOut: 'Explain the concept of zero-knowledge proofs in simple terms' — use up to 300 output tokens and pay per call with USDC on Base, no API key needed.

## When to prefer this

Choose this endpoint when you need on-demand LLM inference without pre-registering for an API key or maintaining a prepaid balance — ideal for autonomous agents that pay per action using x402 USDC micropayments on Base. It is especially useful when you want to route across multiple frontier models (GPT, Gemini, DeepSeek, GLM, Kimi, MiniMax) through a single OpenAI-compatible interface. Prefer it over direct provider APIs when your agent workflow demands trustless, accountless, per-call payment semantics.

## Known failure modes

- Payment rejected or insufficient USDC balance — HTTP 402 with payment requirements
- Invalid model ID — returns 400 with an error indicating the model is not found
- messages array empty or malformed — 400 validation error
- max_tokens or max_completion_tokens too low for the requested task — response may be truncated with finish_reason=length
- Network or upstream model provider outage — 502 or 503 error
- Streaming SSE connection dropped mid-response if stream=true

## How this service works

Fixed-price chat completions for gpt-5.5 on FarOut: flat $0.002 per call (includes up to 4,000 input + 1,000 output tokens). Rate: $0.020/1M input tokens, $0.120/1M output tokens. Pay with USDC on Base using x402. No API key, no account, no prepaid balance.

## Output

Returns an OpenAI-compatible JSON object with a choices array containing the assistant's message and finish_reason, plus a usage object with prompt_tokens and completion_tokens counts.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "model": {
   "type": "string",
   "description": "Model id from GET /v1/models, e.g. glm-5.3. No provider prefix."
  },
  "stream": {
   "type": "boolean",
   "description": "SSE streaming."
  },
  "messages": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "role",
     "content"
    ],
    "properties": {
     "role": {
      "enum": [
       "system",
       "developer",
       "user",
       "assistant",
       "tool"
      ],
      "type": "string"
     },
     "content": {}
    },
    "additionalProperties": true
   },
   "minItems": 1,
   "description": "Chat messages, [OI]-compatible {role, content}."
  },
  "max_tokens": {
   "type": "integer",
   "minimum": 1,
   "description": "Output token budget. Sets your spending cap; actual usage is what gets settled (true-up)."
  },
  "temperature": {
   "type": "number",
   "maximum": 2,
   "minimum": 0,
   "description": "Sampling temperature."
  },
  "max_completion_tokens": {
   "type": "integer",
   "minimum": 1,
   "description": "Alias of max_tokens (gpt-5.x models)."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "usage": {
   "prompt_tokens": 6,
   "completion_tokens": 8
  },
  "choices": [
   {
    "message": {
     "role": "assistant",
     "content": "Hello! How can I help?"
    },
    "finish_reason": "stop"
   }
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/farout-llm-gateway-pay-per-call-chat-completions-gpt-5-5-48b89a9c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from farouter.tech](https://www.zero.xyz/host/farouter.tech/llms.txt)