On September 30, 2026, VolRoc recorded 265,806 active prediction markets across Kalshi and Polymarket, holding $1.98B in combined open interest. Day over day, active markets rose 12.7% and open interest rose 6.9% (vs September 29, 2026). Politics & Elections was the largest domain by open interest (29%), ahead of Sports (20%); together they accounted for 49% of all open interest. Kalshi carried 88% of active markets and Polymarket 12%.
Deterministic · template v1 · 2026-09-30
As of 2026-09-30 · 00:00 UTC
Active Markets
265,806
00:00 UTC freeze
Open Interest
$1.98B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
23,637
with trading activity
Kalshi / Polymarket
88% / 12%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
194,140
Other
27,994
Sports
23,778
Politics & Elections
10,130
Entertainment & Culture
3,051
Crypto & Digital Assets
1,624
Technology & AI
1,345
Economics & Inflation
1,068
Companies & Business
968
World & Geopolitics
773
Monetary Policy
503
Climate & Weather
318
Science & Health
114
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 = 265,806.
Largest Kalshi Series
Cross-category multi-markets
175,654
KXMVECROSSCATEGORY0
18,486
Midterm control
1,620
Votegeneral
1,359
U.S. House races
671
Music — artist streams
636
Nflwins
436
Ncaafwins
434
Nextteamnba
426
Ncaafspread
391
Midtermvoteturn
360
Nflspread
325
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 30, 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 30, 2026.” https://volroc.ai/prediction-markets/2026-09-30/
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