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

# Oracle prices

> How Arcus determines the reference price for each perp market, including external pricing for real-world assets and the off-hours mark price

Each perp market has a reference **oracle price** that represents the fair value of the underlying. The oracle price drives margin, [funding](/concepts/perpetuals/funding), and [liquidations](/concepts/perpetuals/liquidations) — it is the number the system trusts for risk, distinct from the last traded price on the order book.

<Note>
  This page is conceptual. Live prices are available from [`GET /v1/prices`](/api-reference/public/get-live-prices-for-all-markets) and the market-data [WebSocket channels](/api-reference/channels).
</Note>

## Two regimes

How the oracle price is sourced depends on whether a reliable external price is available right now.

| Situation                                            | Oracle price source                                                                  |
| ---------------------------------------------------- | ------------------------------------------------------------------------------------ |
| **Underlying market open** (or a 24/7 crypto market) | Derived from external market data for the underlying.                                |
| **Underlying market closed** (RWA off-hours)         | Derived from the exchange's own mark price, since no reliable external quote exists. |

For crypto, a market is effectively always "open," so the oracle tracks external crypto pricing continuously.

## External pricing for real-world assets

For equities, commodity ETFs, and index ETFs, Arcus references external market data for the underlying while that market is trading. Because cash instruments settle on a delay in traditional markets, the external price is adjusted to a consistent same-day basis so the perp tracks the economics a trader actually experiences. This adjustment is small in normal conditions.

For markets built on futures (such as some commodities), Arcus follows a roll schedule and accounts for the difference between the contracts being rolled out of and into, so the oracle reflects continuous exposure rather than jumping on roll dates. The economic effect of rolls is passed through [funding](/concepts/perpetuals/funding) rather than appearing as an unexplained price gap.

## Off-hours mark price

When the underlying market is closed, there is no live external quote to anchor to. Arcus uses an internal **mark price** — a smoothed average of the order book's own mid price — as the oracle, bounded by the off-hours [price bands](/concepts/perpetuals/funding#off-hours-trading). This lets price discovery continue over nights and weekends while preventing thin liquidity from producing erratic marks.

<Note>
  The exact smoothing windows, sampling, and band parameters are internal risk settings and are not part of the public API. Treat the API's published prices as the source of truth.
</Note>