On September 8, 2026, VolRoc recorded 241,190 active prediction markets across Kalshi and Polymarket, holding $1.88B in combined open interest. Day over day, active markets rose 15.8% and open interest rose 8.1% (vs September 7, 2026). Politics & Elections was the largest domain by open interest (31%), ahead of Sports (22%); together they accounted for 54% of all open interest. Kalshi carried 75% of active markets and Polymarket 25%.
Deterministic · template v1 · 2026-09-08
As of 2026-09-08 · 00:00 UTC
Active Markets
241,190
00:00 UTC freeze
Open Interest
$1.88B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
23,712
with trading activity
Kalshi / Polymarket
75% / 25%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
113,312
Other
66,426
Sports
39,463
Politics & Elections
10,732
Entertainment & Culture
3,130
Crypto & Digital Assets
1,856
Climate & Weather
1,434
Technology & AI
1,359
Economics & Inflation
1,042
Companies & Business
901
World & Geopolitics
890
Monetary Policy
530
Science & Health
115
Venue-agnostic subject taxonomy from Kalshi series prefixes and
Polymarket title keywords. A residual Other bucket is reported honestly.
Yes-price across both venues, 10 buckets from 0 to 100. n = 241,190.
Largest Kalshi Series
Cross-category multi-markets
113,312
—
31,524
Midterm control
1,263
Music — artist streams
734
U.S. House races
643
Nextteamnba
484
Ncaafwins
410
Nflwins
382
Nflspread
357
Ncaafspread
295
Ncaafgame
283
Midtermvoteturn
247
Kalshi market families (Polymarket is not series-structured).
About & Citation
This is the fixed-hour (00:00 UTC) state of every active market on
Kalshi and Polymarket for September 8, 2026. The live
Observatory
shows the current diurnal value; this record is immutable. Open interest combines Kalshi
open interest with Polymarket USD liquidity as comparable USD magnitudes. Sources: Kalshi, Polymarket.
How to cite
“VolRoc Prediction Market Archive — September 8, 2026.” https://volroc.ai/prediction-markets/2026-09-08/
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