A 390-foot superyacht designed to run entirely on liquid hydrogen is poised to make waves at the upcoming Monaco Yacht Show — where it will be listed for sale with a whopping $645 million price tag.

Though never publicly confirmed by Microsoft co-founder Bill Gates, the vessel — named “Breakthrough” and also known as “Project 821” — has long been linked to the billionaire.

Gates, however, has never actually set foot aboard the yacht, according to Luxury Launches.

The Post has reached out to Gates’ reps for comment.

A 390-foot hydrogen-powered superyacht — commissioned by Bill Gates — is hitting the market for $645 million at the Monaco Yacht Show this September.ZUMAPRESS.com

Built by Dutch shipyard Feadship and designed by RWD, the seven-deck vessel took five years to complete and will be the largest yacht on display at the show.

The listing is being handled by yacht brokerage Edmiston.

Dubbed “Breakthrough,” the ultra-luxury vessel boasts a beach club-style infinity pool, a basketball court, a private hospital, a cinema, multiple libraries and hot tubs, along with accommodations for 30 guests across 15 cabins and 43 crew.Edmiston

“This is the one that will change it all,” Jamie Edmiston, the firm’s chief executive said in a press release. “The brief was to build the greenest and most environmentally advanced yacht ever built, without compromise. It was a huge challenge, but one that the team has embraced and delivered on.”

What sets Breakthrough apart is its fuel system: a next-generation hydrogen fuel cell platform that allows the vessel to operate entirely off compressed liquid hydrogen stored below deck at minus 253 degrees Celsius.

The ship’s power plant also recycles heat generated during conversion to warm pools, steam rooms, towel bars and guest-room floors.

For voyages where hydrogen is unavailable, a secondary biofuel system supplies electricity while reducing emissions by 90%.

Gates’ four-story “townhouse within a yacht” includes private elevators, sea terraces and a gym, creating a secluded, residential atmosphere.Edmiston

Designed by RWD and built by Feadship over five years, Breakthrough runs primarily on liquid hydrogen stored at -253°C, making it the world’s first hydrogen-fueled “net zero” yacht, with biofuel backup cutting emissions by 90%.Edmiston

“Fuel cells will play an important role for yachts in the years to come,” Jan-Bart Verkuyl, a director at Feadship said, citing their “superior efficiency, low particle emissions and low noise radiation.”

Beyond its green credentials, the yacht delivers the kind of luxury one might expect at this price point.

The interior is fitted with a blend of leathers, marble, limed oak and rattan, intended to evoke a coastal resort aesthetic.

There’s a full-size basketball court, a cinema, several hot tubs and a private hospital onboard.

Despite the speculation and extensive investment, Gates has reportedly never set foot aboard.Bruce Glikas/WireImage

The owner’s quarters span four private floors and include two bedrooms, twin bathrooms, dressing rooms, two offices — each with a fireplace — a gym, a pantry and a living room.

“It creates, in essence, a secluded four-level townhouse-by-the sea within the much larger yacht,” reads the listing.

Discreet balconies slide out from the hull at the touch of a button, their floors rising to sit flush with the yacht’s interior rooms.

Edmiston notes that “at each deck level, there are inviting private lifestyle destinations to savor,” such as a “coffee corner and games niche,” “a library on the main deck” and “a private dining room with a sea terrace.”

The sale is being handled by Edmiston, whose CEO called it “the one that will change it all.”ZUMAPRESS.com

Canadian billionaire Patrick Dovigi is rumored to be the buyer.Edmiston

In total, Breakthrough can accommodate 30 guests and 43 crew members.

The owner’s deck alone sits 121 feet above the waterline.

While Gates has neither confirmed nor denied his involvement with the project, industry insiders say the yacht was built to his specifications.

Canadian billionaire Patrick Dovigi, CEO of Green For Life Environmental, is reportedly in line to acquire it.