On September 29, 2026, VolRoc recorded 235,884 active prediction markets across Kalshi and Polymarket, holding $1.85B in combined open interest. Day over day, active markets fell 8.6% and open interest rose 125.2% (vs September 28, 2026). Politics & Elections was the largest domain by open interest (31%), ahead of Sports (20%); together they accounted for 51% of all open interest. Kalshi carried 87% of active markets and Polymarket 13%.
Deterministic · template v1 · 2026-09-29
As of 2026-09-29 · 00:00 UTC
Active Markets
235,884
00:00 UTC freeze
Open Interest
$1.85B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
22,411
with trading activity
Kalshi / Polymarket
87% / 13%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
166,489
Other
27,610
Sports
22,137
Politics & Elections
10,115
Entertainment & Culture
2,924
Crypto & Digital Assets
1,548
Technology & AI
1,346
Economics & Inflation
1,070
Companies & Business
951
World & Geopolitics
766
Monetary Policy
507
Climate & Weather
309
Science & Health
112
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 = 235,884.
Largest Kalshi Series
Cross-category multi-markets
154,374
KXMVECROSSCATEGORY0
12,115
Midterm control
1,610
Votegeneral
1,340
U.S. House races
671
Music — artist streams
639
Ncaafwins
433
Nflwins
432
Nextteamnba
426
Midtermvoteturn
352
Ncaafspread
292
Nflspread
286
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 29, 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 29, 2026.” https://volroc.ai/prediction-markets/2026-09-29/
Get the daily statistics
A short daily read on the prediction-market universe across Kalshi and Polymarket.
Join the list →