The members were introduced through a VCR in Exo Planet #3 - The Exo'rdium.
2016: Debut in Korea
On October 5, SM Entertainment announced that EXO would have their first sub-unit, composed by Chen, Baekhyun, and Xiumin, debuting in late October. SM released their first teaser on the 21st, which was called HOT DEBUT : EXO'S FIRST UNIT. On October 23, the sub-unit released an OST for the drama Scarlet Ryo, "For You", at the Busan Asia One Festival.
On the 24th, SM announced the name of the sub-unit will be called EXO-CBX. A teaser for "Hey Mama!" was released on the 30th before their mini album was released the following day.
2017: Debut in Japan
On May 10, through EXO's official Japanese Twitter account, SM announced that the sub-unit was going to have a Japanese debut during late May. They released their debut Japanese mini album, Girls, on May 24.