More office and multifamily buildings would be built on 12.5 acres of surface parking in Boston’s Seaport District under W/S Development’s development plan for the parcels it acquired in late 2015 for $359 million.

In a reflection of the strong demand for office space in the Seaport, W/S Development is seeking to increase the office component previously approved in 2010 from 1.2 million to 2.9 million square feet, and upping the number of residential units from 2,500 to 3,200.

The retail component would be unchanged at 1.1 million square feet, and up to 500,000 square feet of hotel space are proposed, according to a filing with the Boston Planning and Development Agency. Parking spaces would be reduced from 6,500 to 5,500.

Steps from the Summer Street overpass would connect to the new development and a “Harbor Way” pedestrian and bicycle boulevard leading to Northern Avenue and the waterfront. That replaces a street that would have run from Congress Street to Summer Street in the 2010 plan.

Portions of Seaport Boulevard between Sleeper Street and Pier 4 Boulevard would be upgraded with a landscaped medium and tree-lined sidewalks, making the neighborhood’s main drag more pedestrian-friendly, W/S said in the filing. It has hired James Corner Field Operations as landscape architect for the Seaport Boulevard designs.

Civic and cultural spaces – including a performing arts center – would be reduced from 243,000 square feet to 16,200. Arts venues would be interspersed throughout the site, with W/S issuing a request for proposals from cultural organizations to plan either a single facility or group of spaces including a black box performance space, rehearsal areas, studios and makerspaces and art installations.

The changes would increase total development in the 23-acre Seaport Square master-planned district from 6.3 million square feet to 7.7 million square feet. Approximately 3.4 million square feet has been completed or is under construction.