Each trade is bilateral. Futures, both regular and these "perpetual swaps" are zero-sum. A person buying is another person selling and vice versa. The exchange

Each trade is bilateral. Futures, both regular and these "perpetual swaps" are zero-sum. A person buying is another person selling and vice versa. The exchange does not need to hedge the underlying because the exchange/clearing house is a neutral party in the transaction as long as the individual traders are solvent. What it is exposed to is traders blowing up and not being to cover their debts. In case of regular futures, price discovery is aided by the fact that the futures eventually settle to either the underlying or its cash value at a specific point. In perpetual futures, price discovery is aided by "funding fees," which are periodic cash transfers from the side that is contributing to the price discrepancy between the future and the spot to the opposite side. E.g., if perp is below the spot, the short holders will periodically be charged the funding fee, which will go to the long holders, to encourage the shorts to buy/get the price closer to spot, etc.