Nike’s New Super Shoe Was Designed to Take on the World’s Hardest Trails

The brand’s pinnacle trail runner is more comfortable, more versatile and all-around more capable than ever.

Nike

By Jack Seemer

Published August 25, 2025

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Many runners see the marathon as the ultimate test of endurance and determination.

For Caleb Olson, a rising star in ultrarunning, it’s a warmup.

After posting the fastest-ever debut at last year’s Western States, a 100-mile race through the Sierra Nevada mountain range, Olson followed up the feat with a win in 2025.

There can be little doubt about it. Experience and an aggressive strategy were both paramount to his victory.

But Olson also came into the race a few extras arrows in his quiver — or rather on his feet — including Nike’s next super shoe: the ACG Ultrafly.

A male runner wearing a white mesh long-sleeve shirt, a white hydration vest with two water bottles, dark green shorts, and gray running shoes is running on a snowy and rocky trail at dusk. He has a white cap with sunglasses on top and a beard. In the background, a person with long hair, a white cap, and sunglasses is sitting on the snow, holding a camera or phone. The scene includes mountains and a sunset sky. — American ultrarunner Caleb Olsen (pictured) won Western States in a prototype of the ACG Ultrafly.

Served up on a plate

Announced in conjunction with the All Conditions Racing Department — an elite team of Nike-sponsored athletes helping to relaunch ACG as a competitive force in extreme sports — the shoe is easily the brand’s most ambitious trail runner to date.

The new ACG Ultrafly is more than a rebranded version of Nike’s 2023 trail shoe. It’s retooled from the ground up.

Nike

That means it’s much more than a rebranded version of the existing Ultrafly, released in 2023, and went through over a dozen rounds of testing “encompassing more than 30,000 miles,” according to Nike.

“Before Western States, I was planning on wearing the original Ultrafly, but when I received the ACG Ultrafly about two weeks before the race, I put them on and immediately wanted to wear them,” says Shea Aquilano, who is now part of the All Conditions Racing Department.

Both shoes share the same midsole technology, which pairs ZoomX foam with a carbon-fiber plate. However, the latter here differs in a couple of key ways.

Pair of worn, muddy Nike ZoomX running shoes with a beige and black color scheme, featuring visible dirt on the soles and sides, set against a black background. — The 7/8-length plate is thinner than the version found in the original Ultrafly, giving it more flexibility on technical terrain.

For starters, the plate in the ACG Ultrafly is less rigid than the version found in the original. It’s also split down the middle, with a spine that allows it to better bend over roots, rocks and other elements of technical terrain.

According to Brenden McAleese, who oversees footwear at ACG, both variations help to increase the torsional flexibility and control. But the plate’s thinness, in particular, makes the shoe more inclusive.

“We know that no two steps are the same on the trail, and this shoe really allows it to work with the terrain.”

“That was really well received,” he says, “particularly by our lower body weight athletes where they felt they could actually engage the plate that much more. We know that no two steps are the same on the trail, and this shoe really allows it to work with the terrain.”

A man wearing a white long-sleeve mesh shirt, dark shorts, white socks, white running shoes, and a blue cap is running on a treadmill inside a metallic, industrial-looking room. The treadmill has black handrails, and various cameras and sensors are mounted around the treadmill, likely for motion or performance analysis. The room is lit with overhead fluorescent lights and has a black curtain on one side. — Nike claims the ACG Ultrafly went through 13 rounds of testing that covered over 30,000 miles.

Up, up and away

The midsole isn’t the only aspect of the shoe that charts its own course. Nike also retooled the upper to improved breathability and drainability, a boon for ultrarunners who often face multiple water crossings throughout their races.

A pair of worn, dirty athletic shoes with light brown laces and a beige upper featuring subtle line patterns. The shoes have visible dirt marks and scuffs, with the laces untied and one lace end showing a red tip. The shoes are positioned side by side on a black background. — The upper was designed to be more than breathable. Water crossing, which are typical of ultramarathon courses, demand that it’s drainable, too.

But perhaps the most impactful change can’t be seen, only felt — and appreciation for it only goes up as the miles start stacking..

The ACG Ultrafly boasts a brand-new last that features a wider toebox, addressing many runners’ beef with the narrowness of the original Ultrafly.

“Over the course of a hundred miles, really even a few steps, your feet swell and change in shape and size,” McAleese says. “And so this really helps again provide that overall accommodating fit over the course of a run or race.”

The Vibram Litebase outsole is similar to the one on the original Ultrafly. However, the last here is much wider in the toebox, giving the foot room to swell.

Nike

Stiff competition

Having already won Western States, albeit in prototype form, the shoe will make its official debut at the 2025 Ultra-Trail du Mont-Blanc (UTMB) where it will face stiff competition.

On the men’s side, Hoka has won the last two editions with various iterations of its impressively quick Tecton X.

Meanwhile, reigning champ Katie Schide now runs for On, which has a new shoe specifically designed for the course unforgiving climbs.

On Cloudultra Pro running shoe — On’s Cloudultra Pro was designed specifcally for UTMB. Reigning champ Katie Schide will likely wear it during the race.

Regardless of how the ACG Ultrafly ultimately fares, everyday runners will have to exercise patience before they can try a pair for themselves. The shoe doesn’t go on sale until next spring.

Pricing has yet to be revealed but the existing Ultrafly costs $270.

About the Author:

Jack Seemer is the executive editor at Gear Patrol, with over a decade of experience in product journalism. He currently reports on a wide range of topics, including footwear, watches, EDC, cookware and more.