Polymarket US has launched five-minute crypto prediction contracts for Bitcoin, Ethereum, Solana, and XRP, undercutting Kalshi's 15-minute offerings. Each contract pays $1 to the winning side upon settlement. Settlement is determined by index averages rather than spot prices, with ties automatically resolved in favor of "Up." The shorter timeframe positions Polymarket as a faster alternative to Kalshi's existing short-duration crypto markets.