Fallon Co. has scheduled a “top off” ceremony for Thursday morning for its new office tower at Fan Pier in Boston.

According to Fallon, the project is the country’s largest privately-funded development site.

Among those expected to attend the ceremony are Boston Mayor Thomas M. Menino; Joseph F. Fallon, chief executive of Fallon Co.; and Jeff Leiden, chief executive of Vertex Pharmaceuticals Inc.

Currently headquartered in Cambridge, the drug company is planning to relocate. The company received more than $21.8 million in city and state tax incentives for a pair of large office buildings under construction on Fan Pier.

As of January, Vertex had about 2,000 employees worldwide, including 1,375 in Massachusetts. Leiden said then that Vertex should see a significant increase in its workforce in 2012, though he would not specify a number.