On September 26, 2026, VolRoc recorded 370,982 active prediction markets across Kalshi and Polymarket, holding $2.31B in combined open interest. Day over day, active markets fell 3.1% and open interest rose 5.9% (vs September 25, 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 91% of active markets and Polymarket 9%.
Deterministic · template v1 · 2026-09-26
As of 2026-09-26 · 00:00 UTC
Active Markets
370,982
00:00 UTC freeze
Open Interest
$2.31B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
26,895
with trading activity
Kalshi / Polymarket
91% / 9%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
294,776
Other
28,323
Sports
28,157
Politics & Elections
10,150
Entertainment & Culture
3,131
Crypto & Digital Assets
1,482
Technology & AI
1,344
Economics & Inflation
1,019
Companies & Business
897
World & Geopolitics
772
Monetary Policy
496
Climate & Weather
319
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 = 370,982.
Largest Kalshi Series
Cross-category multi-markets
242,283
KXMVECROSSCATEGORY0
52,493
Midterm control
1,551
Votegeneral
1,267
Ncaafspread
899
U.S. House races
667
Music — artist streams
653
Ncaaftotal
637
Nfltd
461
Ncaafwins
437
Nextteamnba
425
Nflwins
407
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 26, 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 26, 2026.” https://volroc.ai/prediction-markets/2026-09-26/
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