On September 7, 2026, VolRoc recorded 208,334 active prediction markets across Kalshi and Polymarket, holding $1.74B in combined open interest. Day over day, active markets fell 29.3% and open interest fell 10.9% (vs September 6, 2026). Politics & Elections was the largest domain by open interest (34%), ahead of Sports (23%); together they accounted for 57% of all open interest. Kalshi carried 70% of active markets and Polymarket 30%.
Deterministic · template v1 · 2026-09-07
As of 2026-09-07 · 00:00 UTC
Active Markets
208,334
00:00 UTC freeze
Open Interest
$1.74B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
23,967
with trading activity
Kalshi / Polymarket
70% / 30%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
85,761
Other
61,458
Sports
39,167
Politics & Elections
10,781
Entertainment & Culture
3,165
Crypto & Digital Assets
1,881
Technology & AI
1,346
Climate & Weather
1,343
Economics & Inflation
1,020
World & Geopolitics
889
Companies & Business
879
Monetary Policy
530
Science & Health
114
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 = 208,334.
Largest Kalshi Series
Cross-category multi-markets
85,761
—
25,902
Midterm control
1,260
Music — artist streams
740
U.S. House races
641
Nextteamnba
514
Ncaafwins
406
Nflwins
381
Nflspread
351
Ncaafspread
254
Ncaafgame
254
Midtermvoteturn
244
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 7, 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 7, 2026.” https://volroc.ai/prediction-markets/2026-09-07/
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