"Goodbye Summer" marks the first time Amber has self-composed a track and also the first time the music producer team NoizeBank has collaborated with f(x) in composition. Gen Neo of NoizeBank handled the arrangement of the piece using mostly acoustic instruments to produce its background music. Amber also raps while the vocalists Luna, Krystal and guest vocalist D.O. of Exo take on the chorus, verses, and belting in the song. Amber initially wrote the lyrics in English, while Kim Young-hoo wrote all-new Korean lyrics (though keeping Amber's English rap section). According to Amber, Krystal was instrumental in getting the song on the album as she advocated for its inclusion after hearing the demo from Amber's music player. Amber would later go on to record an English version of the song with her original lyrics on her solo EP "Beautiful" with guest vocals featuring Eric Nam.