Needham tech company PTC has leased 250,000 square feet at 121 Seaport, a speculative office building under construction by Skanska in Boston.

The company, currently headquartered on Kendrick Street in Needham, said today it will make the move to the waterfront in early 2019. PTC reported $1.1 billion in revenues in fiscal 2016 and has 6,000 employees worldwide.

The 17-story, 400,000-square-foot Seaport tower’s unusual design – with column-free floor plates, 10-foot ceilings and outdoor terraces – and amenities made the choice “an easy one,” PTC CEO Jim Heppelmann said in a statement. In addition to various corporate divisions, the building will host PTC’s “Corporate Experience Center” where customers and business partners demo PTC technology.

The lease calls for base rent of just under $11 million in 2019, with $1 per square foot increases annually through 2037, and additional rent equal to 51 percent of the building’s operating costs and taxes of $5.2 million in the first year, according to an SEC filing. Base rent tops out at $15.4 million in the final year.

PTC will occupy the ninth through 17th floors of the building.

“Attracting younger talent in an ecosystem of technology was paramount for them, and why they moved into the Seaport,” said Charley Leatherbee, head of Skanska’s commercial development operations in Boston.

The elliptical tower designed by CBT Architects attracted some unusual publicity in May 2016 when construction crews unearthed a 19th-century shipwreck during excavation and setting off an impromptu archaeological dig.

Newmark Knight Frank represented Skanska and Cresa represented PTC in the lease transaction.

PTC signed a 10-year lease for 320,665 square feet in three buildings at Boston Properties’ 140 Kendrick St. to house more than 1,000 employees in 2010. As of November 2016, PTC leased 1.4 million square feet of office space in the U.S. and abroad.

Skanska earlier developed the neighboring 101 Seaport office tower, which attracted anchor tenant PwC, before selling the property to Union Investment Real Estate of Germany for $452 million.

This article has been updated with comments from developer Skanska and information on the lease terms.