Unlike stocks, which offer a continuous stream of prices, futures contracts trade in a series of contracts with fixed maturity, generally limited to a duration of a few months. A similar price history for futures, however, can be simulated through the creation of a continuous futures contract which effectively "stitches" together the prices of individual contracts. As multiple contract months often trade simultaneously for a given contact, a decision needs to be made as to which contracts to stitch and when.
IBKR's continuous futures contract applies the prices of the current delivery month and rolls to the following month once the Close-Out Deadline is reached. While this deadline may be prior to the expiration of the current delivery month contract, it's in alignment with the contacts that clients are permitted to trade and generally reflects the contract having the greatest volume and open interest.