So I buy a future for 1 bitcoin in 10 days with a price of $10k. The future is cash settled, so in 10 days the exchange will give me [price of BTC] - $10k, or I can sell the future before then. Where does the bitcoin come in? Is the exchange required to hold bitcoin = to the net of all futures?
For CME (and perhaps NASDAQ) they are doing cash settlement instead of physical settlement of the Bitcoin since it would introduce significant overhead. They are going to use a reference rate called their "Bitcoin Reference Rate" which has a collection of exchanges that it uses to determine the spot price.