On August 31, 2026, VolRoc recorded 185,345 active prediction markets across Kalshi and Polymarket, holding $1.58B in combined open interest. Day over day, active markets fell 17.4% and open interest fell 10.8% (vs August 30, 2026). Politics & Elections was the largest domain by open interest (37%), ahead of Sports (22%); together they accounted for 59% of all open interest. Kalshi carried 68% of active markets and Polymarket 32%.
Deterministic · template v1 · 2026-08-31
As of 2026-08-31 · 00:00 UTC
Active Markets
185,345
00:00 UTC freeze
Open Interest
$1.58B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
22,614
with trading activity
Kalshi / Polymarket
68% / 32%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
89,131
Other
37,652
Sports
36,154
Politics & Elections
10,588
Entertainment & Culture
3,073
Crypto & Digital Assets
1,938
Technology & AI
1,805
Climate & Weather
1,393
Companies & Business
1,077
Economics & Inflation
1,009
World & Geopolitics
850
Monetary Policy
533
Science & Health
142
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 = 185,345.
Largest Kalshi Series
Cross-category multi-markets
89,131
—
2,823
Midterm control
1,218
Music — artist streams
745
U.S. House races
632
Nextteamnba
513
Nflwins
366
Ncaafwins
353
Ncaafspread
342
Ncaafgame
320
Nflspread
309
NFL — next team moves
231
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 August 31, 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 — August 31, 2026.” https://volroc.ai/prediction-markets/2026-08-31/
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