These copper-clad luxury apartment buildings - complete with an amenity-filled skybridge - will gradually turn green over time

There's a new luxury residential development going up at 626 First Avenue in Manhattan, and it's composed of the two largest copper-clad buildings in the world.

Also unusual is that the buildings' 761 units will only be available to rent, not to buy.

The American Copper Buildings are two "dancing" copper-faced towers, connected 300 feet up by a giant, three-story skybridge. That skybridge is the first of its kind to be built in Manhattan in the last 80 years.

And unlike many skybridges, which generally serve as footpaths between buildings, this one is a destination in and of itself: it houses the bulk of the buildings' 60,000 square feet of super-luxury amenities, which include a lap pool, fitness center, lounge, and climbing wall. Residents will also get double-sided views of the Manhattan skyline to the east and Hudson River and Brooklyn to the west.

But it's the exteriors that will probably draw the most attention.

"It's kind of a performance art piece for the city as a whole," said Gregg Pasquarelli, a principal at SHoP Architects, which designed the project. The distinctive copper facing will soon lose its lucky-penny luster and "turn green before our eyes" over the course of the next 20 to 30 years, Pasquarelli said to Business Insider.

The 761-unit project is being developed and constructed by JDS Development Group. Leasing will open up towards the end of 2016, and although pricing has not yet been released, it's likely to fall in line with Manhattan's other major luxury towers, with units ranging from studios to three-bedrooms.