A perpetual swap is a derivative contract with no expiration date that uses a periodic funding payment between long and short holders to keep its price anchored to the underlying spot index. BitMEX introduced the format in 2016 with its XBTUSD contract, and the 8-hour funding mechanism it popularized has since become the standard structure across nearly every crypto derivatives exchange.
Solving the expiration problem
Traditional futures contracts, including those in commodities markets, expire on a fixed monthly or quarterly schedule, which splits trading interest and liquidity across several separate contracts at once. BitMEX's perpetual swap removed the expiration date entirely, letting traders hold a leveraged position indefinitely without needing to roll it into a new contract. That single design choice is a major reason perpetuals now account for the majority of crypto derivatives volume.
The added complexity of inverse contracts
Early perpetual swaps were inverse contracts, meaning they were margined and settled in Bitcoin rather than in US dollars. That created a non-linear payoff for a trader shorting Bitcoin: since profits on a winning short are paid out in an asset that is, by definition, falling in dollar terms during that trade, the actual dollar value of the gain does not scale in a straightforward way with price movement, which caught many early traders off guard.
What backstops the system when things go wrong
Exchanges built multi-million dollar insurance funds specifically to absorb the losses from bankrupt accounts when a sudden price gap skips over a trader's liquidation price entirely. In the rarer case where even the insurance fund runs dry, exchanges fall back on auto-deleveraging (ADL), a mechanism that automatically closes down the highest-profit opposing positions in a queue to cover the shortfall, which is one reason very profitable positions can sometimes get closed unexpectedly during extreme volatility.
- Exchanges built multi-million dollar insurance funds to absorb bankrupt accounts when market gaps skip liquidation stops.
- When the insurance fund is depleted, auto-deleveraging closes the highest-profit positions in the ADL queue automatically.