On September 27, 2026, VolRoc recorded 455,488 active prediction markets across Kalshi and Polymarket, holding $2.37B in combined open interest. Day over day, active markets rose 22.8% and open interest rose 2.7% (vs September 26, 2026). Politics & Elections was the largest domain by open interest (25%), ahead of Sports (17%); together they accounted for 42% of all open interest. Kalshi carried 93% of active markets and Polymarket 7%.
Deterministic · template v1 · 2026-09-27
As of 2026-09-27 · 00:00 UTC
Active Markets
455,488
00:00 UTC freeze
Open Interest
$2.37B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
27,921
with trading activity
Kalshi / Polymarket
93% / 7%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
377,558
Sports
29,365
Other
28,798
Politics & Elections
10,151
Entertainment & Culture
3,138
Crypto & Digital Assets
1,501
Technology & AI
1,344
Economics & Inflation
1,039
Companies & Business
886
World & Geopolitics
770
Monetary Policy
500
Climate & Weather
322
Science & Health
116
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 = 455,488.
Largest Kalshi Series
Cross-category multi-markets
296,853
KXMVECROSSCATEGORY0
80,705
Midterm control
1,562
Votegeneral
1,281
Ncaafspread
927
Ncaaftotal
674
U.S. House races
667
Music — artist streams
649
Nfltd
556
Nflrecyds
519
Ncaafwins
442
Nextteamnba
425
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 27, 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 27, 2026.” https://volroc.ai/prediction-markets/2026-09-27/
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