Boston’s soon-to-be-tallest residential tower has equally soaring condo prices.

Carpenter & Co., the developer behind the Four Seasons Hotel and Private Residences under construction in Back Bay, will price a penthouse duplex at $40M, the Wall Street Journal reports. The unit is the last of the building's three penthouses to go on the market.

Carpenter & Co. CEO Richard Friedman announced in April his company had a different unit under contract for about $40M, which would seize the record for Boston’s most expensive condo sale from John Grayken’s $35M penthouse at downtown’s Millennium Tower. The second penthouse at the Back Bay Four Seasons went under contract in June.

The 7,300 SF duplex will be on the 60th and 61st floors of the tower. The unit features a 570 SF terrace, four bedrooms, five bathrooms and two powder rooms. Should the deal close, it would put upward pressure on Boston’s already astronomical average condo price.

Condo prices have increased 68% over the last six years, with the average price in a full-service building in Boston reaching $2M. Prices at the Four Seasons start at $2.5M.