On September 24, 2026, VolRoc recorded 281,728 active prediction markets across Kalshi and Polymarket, holding $2.01B in combined open interest. Day over day, active markets rose 7.0% and open interest was little changed (vs September 23, 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 88% of active markets and Polymarket 12%.
Deterministic · template v1 · 2026-09-24
As of 2026-09-24 · 00:00 UTC
Active Markets
281,728
00:00 UTC freeze
Open Interest
$2.01B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
24,954
with trading activity
Kalshi / Polymarket
88% / 12%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
207,381
Other
28,189
Sports
26,376
Politics & Elections
10,062
Entertainment & Culture
3,091
Crypto & Digital Assets
1,672
Technology & AI
1,344
Economics & Inflation
1,032
Companies & Business
883
World & Geopolitics
777
Monetary Policy
492
Climate & Weather
313
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 = 281,728.
Largest Kalshi Series
Cross-category multi-markets
174,162
KXMVECROSSCATEGORY0
33,219
Midterm control
1,519
Votegeneral
1,240
Ncaafspread
684
Music — artist streams
662
U.S. House races
654
Ncaaftotal
446
Ncaafwins
437
Nextteamnba
425
Nflwins
407
Midtermvoteturn
309
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 24, 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 24, 2026.” https://volroc.ai/prediction-markets/2026-09-24/
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