Mansour is a co-founder and chief executive of prediction market Kalshi, the largest such platform operating in the US. He has chosen to meet me at Serafina, one of a small chain of Italian restaurants, in Manhattan’s Meatpacking District because it is close to Kalshi’s offices and rarely crowded. The sky above New York is a threatening grey, and Kalshi traders are forecasting a 74 per cent chance of rain.