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An Arcus perp references a few different prices, and it helps to know which does what:
  • Mark price — the exchange’s fair-value estimate for the perp. It’s the number your position is marked at and the sole reference for margin, PnL, and liquidations. Start here.
  • Oracle price — an external view of the underlying’s fair value. It’s an input to the mark price and drives the funding basis; it does not value your position directly.
  • Order-book prices — the last trade price, the best bid and ask, and the impact mid (the average price to fill a fixed reference size on each side). These feed the mark price.
This page is conceptual. Live prices are available from GET /v1/prices and the market-data WebSocket channels.

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Mark price

The mark price is the exchange’s fair-value estimate for a perp, and it is the sole valuation reference for risk: margin, unrealized PnL, and liquidations are all computed from it — there is no oracle fallback. It’s also the number the off-hours price bands constrain. It blends the oracle price with the perp’s own order book, so it tracks where the contract is actually trading without drifting far from fair value. Two inputs feed the calculation:
  • Impact mid — the midpoint of the impact bid and impact ask: the average price to fill a fixed reference size on each side of the book. Using impact prices rather than the top of book keeps the mark robust to a single thin quote.
  • Oracle price — the external reference described below, available for crypto around the clock and for RWA perps during the underlying’s regular trading hours (RTH).

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Markets with a live oracle

Crypto perps (24/7) and RWA perps during RTH. The mark price is the average of two components, then clamped to a tight band around the oracle:
  1. Order-book price — the median of the last trade price, the best bid, and the best ask.
  2. Oracle-anchored price — the oracle price plus a 2.5-minute EWMA of (impact mid − oracle price). This tilts the mark toward where the perp is actually trading.
The average of the two is then clamped to within ±min(10 ÷ leverage, 1)% of the oracle price — at most ±1%, and tighter for higher-leverage markets. The clamp bounds the published mark’s total deviation from the oracle; it is not applied to the EWMA term on its own. (If there’s no recent trade, component 1 drops out and the mark is component 2 alone, still clamped.)

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Markets with no live oracle

RWA perps outside RTH, when the underlying is closed and no reliable external quote exists. The mark price is the 2.5-minute EWMA of the impact mid alone (no oracle clamp), bounded by the off-hours price bands. In this regime funding is also locked to the base rate.
The reference size behind the impact mid, and the exact band parameters, are per-market risk settings read from the API. Treat the API’s published prices as the source of truth rather than recomputing the mark yourself.

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Oracle price

The oracle price represents the fair value of the underlying. It anchors the mark price (above) and drives the funding basis. How it’s sourced depends on whether a reliable external price is available right now. For crypto, a market is effectively always “open,” so the oracle tracks external crypto pricing continuously.

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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 rather than appearing as an unexplained price gap.