On September 1, 2026, VolRoc recorded 236,647 active prediction markets across Kalshi and Polymarket, holding $1.82B in combined open interest. Day over day, active markets rose 27.7% and open interest rose 15.4% (vs August 31, 2026). Politics & Elections was the largest domain by open interest (32%), ahead of Sports (21%); together they accounted for 52% of all open interest. Kalshi carried 75% of active markets and Polymarket 25%.
Deterministic · template v1 · 2026-09-01
As of 2026-09-01 · 00:00 UTC
Active Markets
236,647
00:00 UTC freeze
Open Interest
$1.82B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
24,735
with trading activity
Kalshi / Polymarket
75% / 25%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
136,649
Other
39,556
Sports
38,609
Politics & Elections
10,754
Entertainment & Culture
2,934
Crypto & Digital Assets
1,883
Climate & Weather
1,411
Technology & AI
1,376
Companies & Business
998
Economics & Inflation
985
World & Geopolitics
835
Monetary Policy
533
Science & Health
124
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 = 236,647.
Largest Kalshi Series
Cross-category multi-markets
136,649
—
5,965
Midterm control
1,220
Music — artist streams
741
U.S. House races
632
Nextteamnba
513
Ncaafspread
466
Nflwins
370
Ncaafwins
369
Ncaafgame
332
Nflspread
313
Mlbhrr
305
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 1, 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 1, 2026.” https://volroc.ai/prediction-markets/2026-09-01/
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