On 9 April 2020, Charli XCX announced that "forever" would be released at 07:30 PM BST / 11:30 AM PST and premiere on BBC Radio 1 as Annie Mac's Hottest Record in the World.

The song also features "lo-fi beats and luminous synths" with Charli singing about "an everlasting love that will remain even if the relationship fades away or if they're not physically together".

[18] Variety’s Jem Aswad felt that the song "bears many of the hallmarks of the prolific artist’s work over the past couple of year", including Charli’s two mixtapes.

Calling the melody "indelible", Aswad mentions Cook’s trademark "echoing synthesizers" and how Charli uses auto tune as an "instrument in itself rather than as pitch correction".

James also felt that there was "nothing slapdash" about the track, writing that the lyrics talked about a "part of the compressed reality we’re all experiencing: being trapped in close to someone that you care about" as the single "switches between abrasive and elated", "[choosing] to embrace happiness in the moment".