“929” takes its name from Halsey’s birthday, September 29, 1994. A section of the song’s lyrics were revealed in Rolling Stone’s review of Manic, published 3 days before its release.

Halsey first teased the song on Instagram on August 10, 2019, posting a picture of a new tattoo on her hand: the numbers “929.” The image was initially captioned “🎂track 16,” spurring fans to speculate about her then untitled album.

Halsey later edited the caption to “🎂track 16 / TRACK 2,” connecting to the album’s third single, “clementine,” which was released on September 29, 2019, her 25th birthday.