# PennyRail OpenAI-Compatible Chat Mini

> PennyRail OpenAI-Compatible Chat Mini is a paid API for AI agents from pennyrail.vercel.app, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-15).

Provides an OpenAI-compatible chat completion API endpoint with micropayment settlement via x402, offering a mini/lightweight chat model interface

## Facts

- Endpoint: POST https://pennyrail.vercel.app/api/p/premium/ai.chat-mini--openai-compatible-chat
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/pennyrail-openai-compatible-chat-mini-2c45ad9c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Ur_wSlaOhBQVwaoWkNdr4

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 pennyrail-openai-compatible-chat-mini-2c45ad9c -d '<json body>'
```

Example prompt: Send this message to the mini chat model and get a response: 'Explain the difference between supervised and unsupervised learning in two sentences.'

## When to prefer this

Choose this endpoint when you need an OpenAI-compatible chat completion interface with per-call USDC micropayment billing via x402, avoiding subscription commitments. Ideal for agent pipelines that need lightweight, cost-controlled text generation without managing API key subscriptions. Prefer this over standard OpenAI API when your system already handles x402 payment flows and you want granular per-request cost control.

## Known failure modes

- Payment failure if insufficient USDC balance — returns 402 Payment Required
- Malformed input object causes 400 Bad Request
- Model unavailability or upstream OpenAI outage returns 503 or 500
- Rate limiting may result in 429 Too Many Requests
- Missing required 'input' field returns validation error

## How this service works

Machine-readable settlement service

## Output

Returns a chat completion response in OpenAI-compatible format, containing the assistant's generated message text and any associated metadata such as token usage and finish reason.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "object",
 "additionalProperties": true
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/pennyrail-openai-compatible-chat-mini-2c45ad9c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from pennyrail.vercel.app](https://www.zero.xyz/host/pennyrail.vercel.app/llms.txt)