On September 11, 2026, VolRoc recorded 346,599 active prediction markets across Kalshi and Polymarket, holding $2.13B in combined open interest. Day over day, active markets fell 11.2% and open interest fell 4.3% (vs September 10, 2026). Politics & Elections was the largest domain by open interest (26%), ahead of Sports (20%); together they accounted for 46% of all open interest. Kalshi carried 82% of active markets and Polymarket 18%.
Deterministic · template v1 · 2026-09-11
As of 2026-09-11 · 00:00 UTC
Active Markets
346,599
00:00 UTC freeze
Open Interest
$2.13B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
28,153
with trading activity
Kalshi / Polymarket
82% / 18%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
190,770
Other
91,631
Sports
42,242
Politics & Elections
10,738
Entertainment & Culture
3,180
Crypto & Digital Assets
1,855
Technology & AI
1,430
Climate & Weather
1,267
Economics & Inflation
1,035
World & Geopolitics
893
Companies & Business
888
Monetary Policy
552
Science & Health
118
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 = 346,599.
Largest Kalshi Series
Cross-category multi-markets
190,770
—
55,372
Midterm control
1,284
Music — artist streams
720
Ncaafspread
661
U.S. House races
645
Ncaaftotal
485
Nextteamnba
454
Ncaafwins
422
Nflwins
399
Nfltd
392
Nflspread
354
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 11, 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 11, 2026.” https://volroc.ai/prediction-markets/2026-09-11/
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