Prediction market open interest: where capital actually sits
Capital held in open positions on each prediction market, in USD. Unlike volume it only counts money still at risk, so a venue that trades a lot and settles fast reads small here and a venue holding long-dated markets reads large. The turnover column is the ratio of the two, and the two rank very differently.
TL;DR. As of , Kalshi leads open interest at $1.18B (24h) across 12 ranked venues. Source: OpenChainBench, https://openchainbench.com/benchmarks/pm-open-interest.
Read this carefully
Open interest is not measured the same way everywhere. Venues with a dedicated public API report it natively; the rest are read from DefiLlama's protocol TVL, which is the closest public proxy and is not the same thing. A CFTC-regulated exchange has no on-chain balance and therefore no row when its API does not publish one. Size here says where capital sits, not whether a venue is liquid or well run.
Prediction markets are ranked by volume almost everywhere, and volume is the easier number to move. Open interest is the money still at risk: it only counts positions nobody has closed, so it cannot be inflated by trading a market back and forth. The two disagree sharply across this cohort, and rank it differently. Kalshi holds the largest book of open positions at $1.18B; the venue that trades the most in a day is read from the 24h volume column, and the turnover column beside it says how many times each book turns over. Below 1x is what long-dated markets look like, well above 1x is what short-dated contracts look like, and neither is better. This board publishes the open interest, the volume on both a 24-hour and a 30-day window, and the ratio, so the two readings sit next to each other instead of one standing in for the other.
Methodology
The pm-cohort-stats harness reads each venue from the best source it has, and for open interest that is more often DefiLlama than the venue. Kalshi publishes open interest natively. Polymarket's gamma field is deprecated and reads far below the protocol's tracked value, so Polymarket and Limitless use DefiLlama protocol TVL; Myriad's native figure is AMM liquidity. Every row says on its own tag which source it came from. The rest of the cohort is read from DefiLlama's prediction-market category, where protocol TVL stands in for open interest and /summary/dexs supplies volume. Gauges are pm_venue_open_interest_usd, pm_venue_volume_24h_usd, pm_venue_volume_30d_usd and pm_venue_active_markets, one series per venue, one writer per gauge. The cohort was widened from five venues to seventeen on 2026-09-23; rows below $500,000 of open interest are not ranked, because a venue holding tens of thousands moves by tens of percent on one position. Where a venue's own API can only be read in part, the partial figure is withheld rather than published as a total.
Results: 13 venues measured, 12 ranked by Open interest (24h)
| № | Venues | p50 | Volume 24h | Turnover | Volume 30d | Success | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Kalshi | $1.18B | $458.77M | 0.383x | $13.05B | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2 | Polymarket | $348.65M | $81.98M | 0.229x | $2.19B | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 3 | Rain | $19.05M | — | — | $12.5K | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 4 | Predict Fun | $10.70M | $12.27M | 1.095x | $310.11M | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 5 | OPINION | $3.18M | $3.76M | 1.184x | $274.93M | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 6 | Sport.fun | $2.29M | $124.0K | 0.054x | $4.72M | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 7 | Augur | $1.95M | — | — | — | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 8 | Pascal | $1.88M | — | — | — | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 9 | Levr Bet | $1.88M | — | — | — | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 10 | PredictStreet | $1.37M | $7,694 | 0.006x | $63.77M | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 11 | Overtime | $1.28M | $307.9K | 0.237x | $7.79M | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 12 | Trueo | $853.7K | $510 | 0.001x | $13.0K | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Measured, not ranked: sample below the ranking floor | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| not ranked | Azuro | $137.2K | $42.2K | 0.297x | $3.12M | 100.00% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Frequently asked
Why rank on open interest rather than volume?
Because open interest is the money still at risk. Volume counts every trade including a position opened and closed in the same hour, so it can be moved by trading a market back and forth; open interest only counts what nobody has closed. Both are on the board and they rank the cohort very differently.
What does a turnover above 1x mean?
That the venue traded more than its whole open book in a day, which is the signature of short-dated contracts: markets that open, fill and settle within hours. Below 1x means positions are held rather than traded. Neither is better; they are different products.
Is the open interest measured the same way for every venue?
No, and each row says which source it uses. Kalshi publishes open interest natively. Polymarket and Limitless are read from DefiLlama protocol TVL because Polymarket's own field is deprecated, and Myriad's native figure is AMM liquidity, not positions. The rest are read from DefiLlama protocol TVL, a proxy for a venue with no public field, and not the same measurement.
Why is Polymarket US missing?
Its open interest is not read yet. Polymarket US is a CFTC-regulated exchange with no on-chain balance for DefiLlama to measure, and its own API publishes open interest one market at a time, which this harness does not walk. So it has no row on a board ranked by open interest, even though its volume is among the largest in the category and is published.
Why are small venues excluded?
Because a venue holding tens of thousands of dollars moves by tens of percent on a single position, so a board including them would rank position-opening events. The floor is $500,000 of open interest; venues under it still publish their gauges.
Source code github.com/ChainBench/OpenChainBench/tree/main/harnesses/pm-cohort-stats