In September of every even-numbered year, the minor leagues undergo what is unofficially called the “Affiliation Shuffle.” Major league teams, for the most part, do not own their minor league affiliates. Instead, major and minor league teams agree to a “Player Development Contract” for a two- or four-year deal to host their minor league team. Those contracts run out in September.
The Cubs had two minor league affiliations that expired in 2018. In the first, the short-season A Eugene Emeralds, agreed to sign a new four-year deal with the Cubs on August 17. (Teams can agree to re-sign with their current minor league affiliates before September, but they aren’t allowed to negotiate with other affiliates before then.