In a confirmation of developer Lendlease’s strategy of building the first for-sale units on the booming East Boston waterfront, half of the condominiums at the Slip65 complex under construction went under agreement during the first weekend with prices ranging from $700 to $1,200 per square foot.

Slip65 is the condo component of the Clippership Wharf development, which also includes 365 apartments.

“We are proud to see how Slip65 has been embraced by the market and are especially satisfied to be selling condos for over $1.5 million in East Boston,” Nick Iselin, general manager of development for Lendlease in Boston, said in a statement.

Completion is scheduled for fall 2018. The amenity package includes an extension of the Boston Harborwalk and fitness club.

“To sell 40 units in 36 hours is just an amazing response, and we anticipate similar demand for the second block when it is made available,” Sue Hawkes, managing director of sales agent The Collaborative Cos. of Boston, said in a statement.

The four-building development being built in two phases is billed as the most resilient housing complex ever built on Boston Harbor, with floor plates elevated above FEMA flood map guidelines, flood-proof doors and gates on the ground floor and a 7,000-square-foot living shoreline designed to buffer storm surges.