Predictions.io, a data and comparison service for prediction markets, said identically worded 2026 U.S. midterm questions were trading at materially different prices across venues. On Aug. 28, 2026, "Blue tsunami in 2026?" was priced at 44.5% on Polymarket and 36.0% on Kalshi, while "Blue wave in 2026?" was priced at 82.5% and 74.0%, respectively. Each spread was 8.5 percentage points. Across directly comparable binary markets live on more than one venue, the median difference exceeded four points and nearly half of pairs differed by at least five points. Prices were recorded at 05:08 UTC on Aug. 28, 2026. The findings came as Kalshi, Polymarket and Polymarket US reported combined July volume of $50.59 billion, with Kalshi accounting for roughly 74.5%. New York City opened a probe into both leading venues, a Washington judge ordered Kalshi to halt most wagers in the state, and the CFTC (U.S. derivatives regulator) began an internal review of so-called mention markets. Predictions.io tracks more than 9,700 event pages across 23 categories and offers free fee and odds calculators, while operating no market or exchange and taking no position in contracts.