It was sometime in 2015, on a hiking trail in Hong Kong, that the perpetual swap — also called a perpetual future or a “perp” for short — was born. Ben Delo, the mathematician and co-founder of BitMEX, was walking with a friend called Bavik, a derivatives trader, wrestling with a problem that had been nagging at him for months.

BitMEX had been trying everything. Quarterly futures, monthly futures, weekly futures, 48-hour futures, even a contract that lasted just 24 hours before resetting. Nothing was working. Customers kept complaining that their positions were closing without warning. They wanted something that looked like spot, traded like spot, but gave them the leverage that only a derivatives exchange could offer.

“What if a…