The penthouse at downtown Boston's Millennium Tower luxury condominium building is on the market for $45 million. Image courtesy Sotheby's International Realty.

The highest unit in downtown Boston’s Millennium Tower is back on the market, with an asking price $10 million higher than its 2016 sale price.

The 13,256-square-foot unit occupies the tower’s entire 60th floor, is edged with a terrace that wraps around its north face and contains eight bedrooms and nine bathrooms. The asking price is $45 million.

Michael Moran of Sotheby’s International Realty has the listing.

Irish-American billionaire John Grayken bought the unit in 2016 for $35 million, a $2.5 million discount from list price. Grayken, who grew up in Cohasset, renounced his American citizenship in favor of Irish citizenship in 1999 to avoid paying U.S. income taxes.