“Billions” is last for all the same reasons that “Welcome to My Island” is first. It dissolves into total selflessness, whereas the album opens with total selfishness. The Beach Boys‘ “Surf’s Up” is one of my favourite songs of all time. I cannot listen to it without sobbing. But the non-linear, spiritual, tumbling, open quality of that song was something that I wanted to bring into the song. But “Billions” is really about pure sensuality, about all agenda falling away and just the gorgeous sensuality of existing in this world that’s so full of abundance, and so full of contradictions, humour and eroticism. It’s a cheeky sailboat trip through all these feelings. You know that feeling of when you’re driving a car to the beach, that first moment when you turn the corner and see the ocean spreading out in front of you? That’s what I wanted the ending of this album to feel like: The song goes very quiet all of a sudden, and then you see the water and the children’s choir comes in.

— via Apple Music

A New Yorker profile on Polachek from September 2021 explained the song’s backstory as follows:

[…] One day, Danny L Harle sent her a beat that he’d written, and Polachek heard a melody out of nowhere, oceanic and potent, and started jotting down psychedelic images: a headless angel, an overflowing cup, a pearl inside an oyster. The beat and the images became the song “Billions.” [Polachek said she] “wanted something that captured the afterglow of a reopening.”

[Danny L Harle] sent me this beat that was actually rejected by another artist. It was just a beat, but I was like, “I’m obsessed with this, could we work on it?” The chords and structure poured out of me in like 15 minutes. I felt like I had the sunshine still on my body, and it was just flowing out through this song.

– Caroline Polachek, Dazed

I hate this word with a deep passion, but it’s tantric. Really sparkly, yet kind of stoned. Pupils dilated — moments of total openness. It’s extremely emotional song that has zero story whatsoever. I wanted the listener to feel lost inside the song.

—via Crack Magazine

“Billions” is one of my favorite song structures on the album. It’s seven verses with only two choruses. I wanted to feel lost inside it, without a road map. This song includes a distorted guitar line that twists around in the background, which is actually just me singing through lots of distortion.

—via Spotify Storyline