The song was first teased on Twitter with Gomez teasing the song tweeting "1000 yo sé que piensas en mí y el corazón se te mueve…si tú quieres ir a 1000...".

They tweeted a pre-save link shortly after.

[1][2] Where it composed in the key of C♯ Major, with a fast tempo of 150 beats per minute and runs for three minutes and 44 seconds.

[3] Lyrically, its "about the beauty of true love.

"[2] The official music video for "999" was released on the same day as the song on August 27, 2021.