On September 3, 2026, VolRoc recorded 259,850 active prediction markets across Kalshi and Polymarket, holding $1.93B in combined open interest. Day over day, active markets fell 6.8% and open interest rose 1.3% (vs September 2, 2026). Politics & Elections was the largest domain by open interest (30%), ahead of Sports (21%); together they accounted for 51% of all open interest. Kalshi carried 77% of active markets and Polymarket 23%.
Deterministic · template v1 · 2026-09-03
As of 2026-09-03 · 00:00 UTC
Active Markets
259,850
00:00 UTC freeze
Open Interest
$1.93B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
26,839
with trading activity
Kalshi / Polymarket
77% / 23%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
150,624
Other
46,613
Sports
40,883
Politics & Elections
10,744
Entertainment & Culture
3,007
Crypto & Digital Assets
1,875
Technology & AI
1,356
Climate & Weather
1,295
Economics & Inflation
1,006
Companies & Business
949
World & Geopolitics
847
Monetary Policy
540
Science & Health
111
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 = 259,850.
Largest Kalshi Series
Cross-category multi-markets
150,624
—
11,791
Midterm control
1,233
Ncaafspread
887
Music — artist streams
734
U.S. House races
636
Ncaaftotal
523
Nextteamnba
513
Ncaafwins
380
Nflwins
375
Ncaafgame
367
Nflspread
325
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 3, 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 3, 2026.” https://volroc.ai/prediction-markets/2026-09-03/
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