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October prediction trading surges as platform concentration and contract mix diverge

The October 2026 report, built on Artemis data exported on November 3, puts October trading volume at a record 121.28 billion dollars, up 58.7 percent, with Kalshi combination contracts accounting for 66.78 billion dollars of it. Across the trailing twelve months on the two main platforms, sports contracts made up 43.6 percent of volume while politics and elections held 41.2 percent of open interest on just 4.5 percent of volume.

Prediction-market open interest climbed 41.5 percent to 3.13 billion dollars in October, while trading volume reached a record 121.28 billion dollars, up 58.7 percent, according to VIP Grinders.

The October 2026 report draws on Artemis data exported on November 3. Its figures show trading volume growing faster than open interest, alongside a substantial concentration of event contract activity on two platforms.

Kalshi and Polymarket dominate volume

Kalshi and Polymarket together accounted for 97.7 percent of event contract volume, according to VIP Grinders. That leaves activity outside the two leading platforms representing only a small share of the reported market.

Kalshi combination contracts contributed 66.78 billion dollars to October trading volume—more than half of the 121.28 billion dollar total. Their contribution is therefore central to understanding the record month, rather than treating all contract activity as a single, uniform category.

Sports turnover contrasts with political open interest

Across the trailing twelve months on the two main platforms, sports contracts generated 43.6 percent of volume. Politics and elections, by contrast, accounted for just 4.5 percent of volume but held 41.2 percent of open interest, according to VIP Grinders.

Those category figures describe a different period from the October totals. They nevertheless highlight an important distinction for readers: the categories generating the most trading activity are not necessarily those accounting for the largest share of open interest.

What it means for prediction markets

  • Volume and open interest tell different stories: October’s 58.7 percent increase in volume exceeded the 41.5 percent rise in open interest; the measures should not be treated as interchangeable.
  • Contract mix matters: Kalshi combination contracts supplied more than half of October’s reported volume, making them a major component of the headline growth.
  • Activity is highly concentrated: With Kalshi and Polymarket accounting for 97.7 percent of event contract volume, the aggregate figures largely reflect those two platforms.
  • Category comparisons require care: The trailing-twelve-month split shows sports leading in volume share while politics and elections carry a much larger share of open interest than of trading volume.
KalshiPolymarketInfiniti MarketsInfiniti Signals

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