An expert committee of architects has declared New York's new World Trade Centre tower is now the tallest building in the US, surpassing Chicago's Willis Tower.
The Height Committee of the Council on Tall Buildings and Urban Habitat announced its decision in Chicago.
The committee is widely recognised as the final arbiter of official building heights around the world.
It has been studying whether a design change means the needle atop 1 World Trade Centre is part of the actual building or merely the equivalent of a broadcast antenna.
The tower built on the site of the 9/11 attacks stands at a symbolically important 1,776 feet tall including the 408-foot needle. It officially would have been considered 1,368 feet tall without the needle.
Willis Tower is 1,451 feet tall.
Dubai's Burj Khalifa is the tallest building in the world at 2,717 feet. With Tuesday's decision, the Willis Tower will be the 10th tallest after the new World Trade Centre opens, according to the council. 1 World Trade Centre is the third tallest building in the world.
At stake was more than just bragging rights in two cities that feast on superlatives and the tourist dollars that might follow: 1 World Trade Centre stands as a monument to those killed in the September 11 2001 attacks.
The building's 1,368 feet height without the needle also holds symbolism; it is the height of the original World Trade Centre.
The 30 Height Committee members are industry professionals from all over the world and the body conferred behind closed doors last week in Chicago, where the world's first skyscraper appeared in 1884.
The new World Trade Centre tower remains under construction and is expected to open next year.
The designers had originally intended to enclose the mast's communications gear in decorative cladding made of fibreglass and steel. But the developer removed that exterior shell from the design, saying it would be impossible to properly maintain or repair. Without it, the question was whether the mast was now primarily just a broadcast antenna.
Under the council's current criteria, spires that are an integral part of a building's aesthetic design count. Broadcast antennas that can be added and removed do not.
Daniel Safarik, an architect and spokesman for the nonprofit council, said it might consider amending its height criteria. Such a move would have much broader implications that could force a reshuffle in the rankings of the tallest buildings in the world.