> ## Documentation Index
> Fetch the complete documentation index at: https://docs.roxom.com/llms.txt
> Use this file to discover all available pages before exploring further.

# US500-BTC

> Specific details for the US500-BTC perpetual futures contract.

| **Contract Code**                                               | `US500-PERP`                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| --------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Underlying Indices**                                          | • **Equity leg:** Composite price for the **SPDR S\&P 500 ETF (SPY)** from primary-listing venues <br />• **BTC Price:** 3-venue 4-hour V-WAP spot composite of Binance (BTC/USDT); Bybit (BTC/USDT); Coinbase (BTC/USD).                                                                                                                                                                                                                                                                                                                          |
| **Contract Size**                                               | Notional of **10 × SPDR S\&P 500 ETF (SPY) point,** quoted & settled in BTC                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| **Quote / P\&L Currency**                                       | BTC                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| **Tick Size**                                                   | 0.01                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| **Trading Hours**                                               | **24 / 7 continuous order book.**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| **Underlying Cash‑Market Hours**                                | **Monday – Friday** <br />• **Pre‑Market:** 04:00 – 09:30 ET <br />• **Regular Session:** 09:30 – 16:00 ET <br />• **After‑Hours:** 16:00 – 20:00 ET *(NYSE Arca consolidated tape; closed on U.S. market holidays).*                                                                                                                                                                                                                                                                                                                              |
| **Mark-Price Construction**                                     | \*\*Mark Price = median(P¹, P², P³), Where: \*\*<br />**Price 1 (P¹)** = Index Price × 1+LastFundingRate×(TimeUntilFunding/8) <br />**Price 2 (P²)** = Index Price plus a rolling **2.5-minute average basis**, where the basis is defined as *(Bid1 + Ask1)/2 − Index Price*. <br />**Price 3 (P³)** = Last traded price.                                                                                                                                                                                                                         |
| **Price Formation when the underlying equity market is closed** | • **Equity leg (SPY):** When U.S. equity exchanges are closed, the equity‑leg reference is **frozen at the last official SPY print** (primary‑listing venues' closing last price). <br />• **BTC leg:** The BTC component continues to update in real time using our 3‑venue 4‑hour VWAP composite (Binance BTC/USDT, Bybit BTC/USDT, Coinbase BTC/USD). <br />• **Mark Price:** mark price is calculated in the same way as during normal trading hours, where each *P* is computed with the **static SPY close** and the **live BTC composite**. |
| **Funding Snapshots**                                           | 00:00 UTC • 08:00 UTC • 16:00 UTC (every 8 h)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| **Funding-Rate Formula**                                        | **Premium Index + Interest Rate**; Interest Rate = 0.03% / day (0.01% / 8 h). Caps ± 3 % per 8 h.                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| **Leverage & Margin**                                           | Max Leverage 10x; Maintenance margin 25% of Initial Margin.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| **Liquidation Logic**                                           | • Trigger when Equity \< MM. <br />• For long positions = Entry Price × (1−Initial Margin Rate + Maintenance Margin Rate) <br />• For short positions = Entry Price × (1 + Initial Margin Rate - Maintenance Margin Rate)                                                                                                                                                                                                                                                                                                                          |
| **Order Types / TIF**                                           | Limit, Market, GTC, GTD, IOC.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| **Min / Max Order Sizes**                                       | **Market Max:** 0.5 BTC <br />**Limit Max:** 0.5 BTC                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |