Comcast Corp.'s new, unfinished tower is now officially the tallest building in the city.

Construction and Comcast officials confirmed what the naked eye could tell in recent weeks. The new tower surpassed the old one in height: 1,050 feet for the new tower, or 75 feet taller than the Comcast Center, the company's headquarters and until now the highest Philadelphia high-rise.

The new tower — which will house the cable giant's engineering and product-development teams and will be topped with a luxury Four Seasons hotel — will eventually reach 1,121 feet.

"While it's not at its ultimate height, it is the tallest building in the city," John Gattuso, a regional director and senior vice president at Liberty Property Trust, which jointly owns the building with Comcast and which is managing the construction, said  Monday.

Officials did not know the exact day that the new tower reached the milestone.

Gattuso said that about two-thirds of the offices in the new Comcast tower have been completed and could be occupied by spring.

The Four Seasons won't open until late 2018. The luxury hotel will occupy the top 12 floors of the 60-story tower. The check-in lobby will be on the top floor, with a restaurant that will have a 360-degree view of the city.

Comcast announced the construction of the tower in early 2014 as part of what it calls an "urban campus" around 18th and Arch Streets. It's a $1.2 billion project and, when completed, the new tower is expected to be the tallest office building between Manhattan and Chicago.

Comcast employees now working in leased office space, much of it in the former Bell Atlantic building, now named Three Logan, will relocate to the new tower.