On September 4, 2026, VolRoc recorded 274,665 active prediction markets across Kalshi and Polymarket, holding $2.01B in combined open interest. Day over day, active markets rose 5.7% and open interest rose 4.0% (vs September 3, 2026). Politics & Elections was the largest domain by open interest (29%), ahead of Sports (21%); together they accounted for 50% of all open interest. Kalshi carried 78% of active markets and Polymarket 22%.
Deterministic · template v1 · 2026-09-04
As of 2026-09-04 · 00:00 UTC
Active Markets
274,665
00:00 UTC freeze
Open Interest
$2.01B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
25,828
with trading activity
Kalshi / Polymarket
78% / 22%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
161,506
Other
49,768
Sports
41,616
Politics & Elections
10,781
Entertainment & Culture
3,159
Crypto & Digital Assets
1,858
Technology & AI
1,360
Climate & Weather
1,220
Economics & Inflation
1,010
World & Geopolitics
875
Companies & Business
861
Monetary Policy
535
Science & Health
116
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 = 274,665.
Largest Kalshi Series
Cross-category multi-markets
161,506
—
14,620
Midterm control
1,244
Ncaafspread
1,064
Music — artist streams
732
Ncaaftotal
717
U.S. House races
638
Nextteamnba
513
Ncaafwins
387
Ncaafgame
386
Nflwins
379
Nflspread
334
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 4, 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 4, 2026.” https://volroc.ai/prediction-markets/2026-09-04/
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