It's a big day for bitcoin. The Cboe began trading the first bitcoin futures on Dec. 10, and that first contract expires Wednesday, and the initial CME contract expires on Jan. 26.

Investors will be watching to see how smoothly the Cboe contract closes.

Investors in many futures products will typically roll over their contract into the next month, but with bitcoin nothing is certain.

There have been some vague concerns that because bitcoin futures are settled in cash, it might be possible for investors to push around the futures contracts at the close simply by aggressively buying and selling. Maybe, but presumably if the futures prices got out of whack with the cash, arbitragers will step in.