It won’t be cheap to replace Top of the Hub.

Boston Properties plans to spend more than $125M over two years upgrading the top three floors of the Prudential Tower, but the developer isn’t ready to divulge exact details on what is going to replace the Top of the Hub restaurant and Skywalk Observatory.

“We anticipate spending in excess of $125M creating an extraordinary experience for local area residents and visitors to Boston,” Boston Properties President Doug Linde said Wednesday on an earnings call. “And we hope to open this public facility in mid-2022.”

Boston Properties opted not to extend a lease with Select Restaurants Inc. to operate the restaurant and observation deck, the restaurant company announced earlier this month. Top of the Hub has operated for 54 years on the 52nd floor of the tower and is slated to close in April.

Linde said the REIT hasn’t decided yet how it will operate the observation deck. He added Boston Properties had considered adding an observation deck while developing Salesforce Tower in San Francisco but plans never panned out. No other observation decks are currently planned at Boston Properties’ assets, Linde said.