The tower's builders say it will surpass Chicago's Willis Tower as the tallest building in the United States, with a final height of 1, 776 feet -- a nod to the year of the Declaration of Independence.

CNN: Obama signs beam of One World Trade Center

The tallest building in the United States, the Willis Tower in Chicago, Illinois, stands 1, 450 feet high.

CNN: STORY HIGHLIGHTS

If it didn't have the spire, One World Trade Center would be shorter than the Willis Tower in Chicago, which stands at 1, 451 feet and currently has the title of tallest building in the U.S., not including its own antennas.

WSJ: Spire permanently installed on WTC tower