On December 11, 2018, YG Entertainment published a group poster with the words "Coming Soon". Two days later, it was revealed that Winner's comeback would consist of a single album that would be released online on December 19. On December 14, it was announced that the single was entitled "Millions" through a poster crediting Kang Seung-yoon, Song Min Ho and Lee Seung Hoon for the lyrics and Kang Seung-yoon, Kang Uk-jin and Diggy for the composition of the song.
Solo posters of the members were released on December 17 and a final poster was published a few hours prior to the release along with a teaser of the music video. The group held an hour-long comeback special live "Merry Millions Day" on Naver's V App on December 19 at 5 PM (KST). The music video was released at 6PM (KST). The making film was published the following day. A performance video with he full choreography was released on December 21.
Tamar Herman of Billboard describes "Millions" as a "feel-good dance track that brings a summery feel" and that is "fronted by plucky strings, snappy drum beats, and bright whistle synth effects." Woo Jae-yeon of Yonhap News Agency defines it as "a tropical-pop dance song."