Boston's One Dalton tower under construction.

A topping-off ceremony was scheduled today for the 742-foot Four Seasons Hotel & Private Residences at One Dalton St. in Boston’s Back Bay, a luxury condominium and hotel tower developed by Carpenter & Co. of Cambridge.

In a recent interview, Carpenter & Co. CEO Richard Friedman told Banker & Tradesman that two of the building’s three penthouses are under agreement, one for $40 million. Units on the top 12 floors have balconies providing views to Cape Cod, and penthouses come with 600-square-foot terraces.

Designed by Henry Cobb of Pei Cobb Freed & Partners and Cambridge Seven Assoc., the triangular tower next to Christian Science Plaza will be the tallest residential building in New England, with 160 residences managed by Four Seasons and 215 hotel rooms on the lower floors. Completion by Boston-based Suffolk Construction is scheduled for early 2019.

The foundation of the concrete-framed building is sunk 165 feet into bedrock, and a 40,000-gallon “slosh tank damper” in the rooftop mechanicals minimizes the movement of the tower during high winds.

“One Dalton is an architectural icon that will transcend generations,” Cobb said in a statement. “Moreover, the tower represents the capstone of my architectural journey in Boston four decades after designing what is formerly known as the Hancock Tower.”

The condo lobby was designed by French architect Thierry Despont. Boston-based landscape architect Michael Van Valkenburgh designed a 5,000-square-foot public park.