# fly.ai Pay-Per-Request Brain API

> fly.ai Pay-Per-Request Brain API is a paid API for AI agents from flyai-x402.fly.dev, paid per call via x402, $0.05/call, status unknown (last checked 2026-10-12).

Answers a single natural language question or prompt via AI, billed per-request at $0.05 USDC over x402

## Facts

- Endpoint: GET https://flyai-x402.fly.dev/brain?utm_source=zero.xyz
- Price: $0.05/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fly-ai-pay-per-request-brain-api-3c7fa318
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_3vIVuFmrL_daatyTWqYee

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 fly-ai-pay-per-request-brain-api-3c7fa318
```

Example prompt: Ask fly.ai's brain a question for me — use seed 42 and the message 'What are the three most important things to know about compound interest?' with sense set to 'finance'.

## When to prefer this

Choose this endpoint when you need a single, ad-hoc AI-generated answer without a subscription, especially in micropayment or x402-compatible agent pipelines. Ideal for agents that need to pay only for what they use and want per-query billing in USDC. Prefer it over subscription-based LLM APIs when cost isolation per question is important.

## Known failure modes

- Payment not sent or insufficient USDC causes 402 Payment Required response
- Missing or malformed 'message' parameter results in an error or empty response
- Invalid seed value (non-integer) may cause a bad request error
- Network or server unavailability on fly.dev returns 5xx errors
- Ambiguous or unsupported 'sense' value may produce unexpected output style

## How this service works

Single answers, each paid on its own over x402. Guide: https://www.flyaiworld.com/x402-api.md

## Output

A text response from the AI answering the provided message, shaped by the sense context and optionally seeded for reproducibility. The response schema is open-ended, returning whatever the AI generates for the given prompt.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "seed": {
   "type": "integer"
  },
  "sense": {
   "type": "string"
  },
  "message": {
   "type": "string"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fly-ai-pay-per-request-brain-api-3c7fa318/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from flyai-x402.fly.dev](https://www.zero.xyz/host/flyai-x402.fly.dev/llms.txt)