One Vanderbilt has reached a huge milestone as construction has topped out on the supertall commercial skyscraper’s tiered steel crown. Workers will soon begin assembly of the 100-foot-tall architectural spire, which will bring the project’s total height to 1,401 feet. Designed by Kohn Pedersen Fox and developed by SL Green, the 77-story Midtown East tower will have a three-story indoor and outdoor public observatory situated at 1,020 feet above street level. Construction of the spire could conceivably finish before the end of the week, given the tremendous speed with which One Vanderbilt has shot upward into the sky.