Repeating her world-class pin-up feat for a second consecutive year, the 20-year-old, 5-feet-10-inch Upton graces the cover of the 2013 edition, which is set to be officially unveiled Monday night on TV on CBS' "Late Show with David Letterman" (with 10 of the models presenting the Top Ten List).
The new edition — marking the 50th anniversary — will be on newsstands Tuesday.
It's Upton's third appearance in a Swimsuit issue. She was chosen as rookie of the year in 2011, when Irina Shayk was on the cover.
This year for the first time, the fashion shoot covers the entire world, with 17 Sports Illustrated Swimsuit models journeying to all seven continents. Photo sites include African dunes and Asian cliffs.
But for Upton, there's lots of ice. She is warming things up in Antarctica, where the cover shot displays her clad only in a white, fur-lined parka and bikini bottom.
Out of a dozen or so photos in which she appears, the cover shot "is the most clothes I'm wearing in the whole issue," Upton said in a phone interview Monday. "It was a sort of I-love-you from the editor: 'I'll let you wear a coat for this one.'"
The shoot spanned 10 days in December, which is Antarctica's "summer." Some of the photos, including the cover, were shot from the base ship, which also carried the team from one icy land shooting site to another.
When she returned to her home in Florida, Upton said she was "very, very sick. I don't think you can go to Antarctica and stand in a bikini without that happening. But I didn't die, and I'm OK now."
Very OK, after hearing only on Friday that she was the editors' choice for the cover.
Despite the challenges of the assignment, Upton said it would likely remain her most thrilling ever, and called Antarctica "the most beautiful place I've ever been."
But for anyone else who wants to experience that magical place, she offered this bit of advice: "You are definitely recommended to keep your clothes on."