Workers of the Freedom Tower erected steel columns that made the skyscraper just over 1,250 feet high, which is just enough to peek over the Empire State Building's observation deck.
The milestone is preliminary. The tower won't reach its full height for another year once workers have added more floors. It is likely to be declared the tallest building in the country and the third largest in the world.
There is debate over the title, however. A 408-foot needle that will sit on the tower's roof falls under an ongoing disagreement among experts and architects about where to stop measuring a tall building with objects extending above the roof.
Taking the needle out of account, the Freedom Tower takes second to the Willis Tower in Chicago.
The Associated Press contributed to this report.