Futures contracts expire on a designated date, referred to as the “expiration date.” Each Fund typically will invest in “lead month” contracts. Lead month contracts are the monthly contracts with the earliest expiration date. Bitcoin futures contracts listed on the CBOE Futures Exchange (“CFE”) or Chicago Mercantile Exchange (“CME”) will be cash settled on their expiration date unless they are “rolled” prior to expiration. Each Fund generally intends to “roll” its bitcoin futures contracts prior to expiration to the next “nearby” bitcoin futures contract. The “nearby” contracts are those contracts with the next closest expiration date. The Funds will incur the costs (or benefits) of continually rolling into the new lead month contracts.
There's a lot of ins and outs which can get confusing in arbitrage trading. We won't go into the technicals of why futures contracts trade at a premium to spot price. You can read a full explanation here. If it's not of interest to you, all you need to know is that there's a tendency, the further out in time the futures contract expires, for the premium to spot to be higher and higher in nominal percentage terms.