On September 23, 2026, VolRoc recorded 263,226 active prediction markets across Kalshi and Polymarket, holding $2.01B in combined open interest. Day over day, active markets rose 12.7% and open interest rose 14.2% (vs September 22, 2026). Politics & Elections was the largest domain by open interest (29%), ahead of Sports (18%); together they accounted for 47% of all open interest. Kalshi carried 87% of active markets and Polymarket 13%.
Deterministic · template v1 · 2026-09-23
As of 2026-09-23 · 00:00 UTC
Active Markets
263,226
00:00 UTC freeze
Open Interest
$2.01B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
24,190
with trading activity
Kalshi / Polymarket
87% / 13%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
189,033
Other
28,118
Sports
26,470
Politics & Elections
10,022
Entertainment & Culture
3,022
Crypto & Digital Assets
1,631
Technology & AI
1,344
Economics & Inflation
1,028
Companies & Business
872
World & Geopolitics
779
Monetary Policy
489
Climate & Weather
301
Science & Health
117
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 = 263,226.
Largest Kalshi Series
Cross-category multi-markets
167,922
KXMVECROSSCATEGORY0
21,111
Midterm control
1,503
Votegeneral
1,227
Music — artist streams
667
U.S. House races
653
Ncaafspread
580
Ncaafwins
435
Nextteamnba
425
Nflwins
404
Ncaaftotal
378
Mlbhit
321
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 23, 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 23, 2026.” https://volroc.ai/prediction-markets/2026-09-23/
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