On September 5, 2026, VolRoc recorded 301,349 active prediction markets across Kalshi and Polymarket, holding $2.08B in combined open interest. Day over day, active markets rose 9.7% and open interest rose 3.5% (vs September 4, 2026). Politics & Elections was the largest domain by open interest (28%), ahead of Sports (21%); together they accounted for 49% of all open interest. Kalshi carried 80% of active markets and Polymarket 20%.
Deterministic · template v1 · 2026-09-05
As of 2026-09-05 · 00:00 UTC
Active Markets
301,349
00:00 UTC freeze
Open Interest
$2.08B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
27,628
with trading activity
Kalshi / Polymarket
80% / 20%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
182,898
Other
53,704
Sports
43,041
Politics & Elections
10,805
Entertainment & Culture
3,169
Crypto & Digital Assets
1,798
Technology & AI
1,370
Climate & Weather
1,254
Economics & Inflation
961
World & Geopolitics
883
Companies & Business
817
Monetary Policy
535
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 = 301,349.
Largest Kalshi Series
Cross-category multi-markets
182,898
—
17,960
Midterm control
1,246
Ncaafspread
1,051
Music — artist streams
740
Ncaaftotal
711
U.S. House races
638
Nextteamnba
513
Ncaafwins
394
Mlbhrr
387
Nflwins
380
Ncaafgame
374
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 5, 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 5, 2026.” https://volroc.ai/prediction-markets/2026-09-05/
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