Artemis tracks prediction markets (event-contract venues where users trade binary outcomes that settle to $1 if an event resolves true and $0 otherwise) on the same framework as exchanges: daily volume, open interest, transactions, and active users. On-chain venues are indexed from raw fills; centralized venues come from each exchange’s official settlement feed. For per-venue data sources and full methodology, see Prediction Markets.
Metrics
Not every venue exposes every metric: MAKER_REBATES and COMBO_VOLUME are venue-specific, and the category splits are populated for the largest venues. TVL is the collateral a venue custodies on-chain, so it exists only for on-chain venues: Polymarket reported $326.1M and Opinion $3.7M on 2026-08-01, while the centralized venues return no value. Check with GET /supported-metrics/.
Covered venues
All 11 venues above return SPOT_VOLUME.
Reading volume across venues
On most venues event contracts are $1-face binaries, so a traded-contract count equals USD notional, directly comparable across Kalshi, Polymarket, ForecastEx, Gemini, Rothera and HIP-4.Nadex and CME are the exception. Their contract faces vary by product family, so SPOT_VOLUME is a raw contract count that does not convert to USD and must not be compared 1:1 with the $1-face venues.SPOT_VOLUME is notional, not the price-weighted premium actually traded (roughly half of notional at typical prices).Perpetual futures on Kalshi and Polymarket are USD-native and live in separate PERP_VOLUME / PERP_OPEN_INTEREST fields. Never add them to event-contract SPOT_VOLUME.
Example: Volume and open interest
Nadex is shown in contracts rather than dollars, per the caveat above.
Split volume by category
Kalshi and Polymarket carry a cross-venue-comparable category taxonomy:
Kalshi’s 2026-08-01 volume across 17 categories, top six:
Sports is 77% of the day’s volume. The same cut works on OPEN_INTEREST.
For a fuller walkthrough see Prediction markets recipe. 