# Bitcoin Smart Fee Curve API

> Bitcoin Smart Fee Curve API is a paid API for AI agents from api.carbon-cashmere.de, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-14).

Returns Bitcoin smart-fee estimates across 1/3/6/12/24/144-block confirmation targets with trend classification derived from a 2-hour moving average, sourced from an own-node estimatesmartfee call.

## Facts

- Endpoint: GET https://api.carbon-cashmere.de/v1/btc-derivatives/fee-curve
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/api-carbon-cashmere-de-843fdcc5
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_b1oVCzM1eo-2rMUtx8J3i

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 api-carbon-cashmere-de-843fdcc5
```

Example prompt: What are the current Bitcoin fee rates for 1, 6, and 24-block confirmation targets, and is the fee market trending rising, stable, or falling right now?

## When to prefer this

Use this endpoint when an AI agent needs real-time Bitcoin fee data across multiple confirmation horizons in a single call, especially for fee-aware transaction timing or execution planning. Prefer this over generic mempool explorers when you also need trend classification (rising/stable/falling/surging) to decide whether to transact now or wait. Ideal for automated agents that must optimize BTC transaction costs dynamically.

## Known failure modes

- Node connectivity issue — own Bitcoin node temporarily unavailable, returns 503
- Fee estimation unavailable — mempool insufficient data for certain block targets, partial curve returned
- Rate limiting — exceeded call quota, returns 429
- Invalid endpoint path — returns 404

## How this service works

Bitcoin smart-fee curve for 1/3/6/12/24/144-block confirmation targets + trend classification (rising/stable/falling/surging) from 2h moving average.

## Output

A fee curve object containing sat/vByte fee estimates for each of the 1, 3, 6, 12, 24, and 144-block confirmation targets, a trend classification label (rising/stable/falling/surging) derived from a 2-hour moving average, and min relay fee context — all sourced live from an own Bitcoin node's estimatesmartfee RPC.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "properties": {
   "type": "string"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "trend": "stable",
  "sat_vb": {
   "1block": 4.2,
   "3block": 3.1,
   "6block": 2.8,
   "12block": 2.5,
   "24block": 2.1,
   "144block": 1.4
  },
  "pressure": "low",
  "min_relay_fee_sat_vb": 1
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/api-carbon-cashmere-de-843fdcc5/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.carbon-cashmere.de](https://www.zero.xyz/host/api.carbon-cashmere.de/llms.txt)