Palmeiras vs. Cerro Porteño Arbitrage Hits 1076% on Paper, But Expiry Mismatches Loom Large

Theoretical yields across Kalshi and Polymarket look massive today, but execution is the main bottleneck. The top gap—SE Palmeiras vs. Club Cerro Porteño—presents a 1076.47% spread on paper. However, with today's date at June 21, 2026, both the Polymarket contract (expired May 21) and the Kalshi contract (expired June 4) are past settlement. This is a classic stale-book trap with no reported volume. For active traders, the real risks lie in the extreme expiry mismatches across the political lines. On the Florida Republican Gubernatorial Primary, Byron Donalds is priced at 6.0¢ on both sides (Poly NO vs. Kalshi YES), yielding a theoretical 733.33% return. The catch: Polymarket settles in August 2026, while Kalshi's contract doesn't expire until August 2027. Locking up capital for an extra year to resolve this leg destroys capital efficiency and introduces severe holding-cost risk. Similar 12-month mismatches are present on the French Presidential candidates and the GA-04 House Race. Before executing, check order book depth. Zero reported volume across these spreads suggests you will face high slippage on any size above micro-bets.