Concrete is finally hitting the dirt at 343 Madison Avenue, where crews are forming the first sections of the foundation slab. The Kohn Pedersen Fox-designed office tower beside Grand Central has officially shifted from digging to building, on the site that once housed the Metropolitan Transportation Authority’s Madison Avenue headquarters. With fresh slabs now visible, Midtown East neighbors are getting their clearest sign yet that this long-planned project is turning into a very literal concrete reality.
Foundations and site progress
As reported by New York YIMBY, excavation and foundation work are advancing on the block between East 44th and East 45th Streets, with the first slab sections forming at the northern end of the lot. Site photos and coverage show excavators still clearing rubble and soil below grade while crews prep the foundation and the new subterranean links that will connect directly into the Grand Central Madison concourse. The development is described at roughly 844 feet tall and is slated to yield about 950,000 square feet of office space.
Developer and design
In a July 29, 2025 press release, BXP said it had launched full vertical construction and billed 343 Madison as a roughly 46-story, 930,000-square-foot premier workplace with hospitality-forward amenities and a direct connection to Grand Central. The company pointed to a double-height, client-exclusive club on the upper floors, lobby cafés, bicycle facilities and expansive terrace space. BXP also flagged a letter of intent with an institutional tenant expected to take about 30 percent of the building.
Sustainability goals
According to New York YIMBY, 343 Madison is being engineered as a fully electric, zero-carbon building and has already secured LEED Platinum and WELL Core certifications while targeting WiredScore Platinum and an Energy Star score of 85 or higher. Renderings show a glass curtain wall accented with vertical metal fins and setbacks topped with landscaped terraces, bringing daylight and outdoor amenity space to the upper floors. The package puts the project squarely in the current race to pair trophy office towers with aggressive environmental and wellness benchmarks.
Transit access and public benefits
The redevelopment is tied to a public-private deal with the MTA to deliver a new accessible street entrance to Grand Central Madison at 45th Street and Madison Avenue, an improvement the authority highlighted when it broke ground on the entrance in October 2024. The MTA described the entrance as a way to ease pedestrian circulation and generate ground-rent revenue earmarked for its capital program. The new street access is being coordinated with the tower’s below-grade construction so commuters will eventually be able to walk directly from the sidewalk into the Madison concourse.
Leasing and market context
Tenants are starting to follow the rebar and concrete. The Real Deal reported that global insurer and investment firm Starr inked a roughly 275,000-square-foot, 20-year lease at 343 Madison, taking floors 16 through 27 and locking down about 30 percent of the tower. Industry coverage has framed the lease as a notable vote of confidence in high-end Midtown office space and a boost for financing and future leasing efforts as construction continues. With Starr in place as a marquee tenant, BXP has a visible anchor to market around while the slabs and subterranean connections move ahead.
Timeline and what's next
BXP’s investor materials project a 2029 delivery, and the developer’s July 2025 release similarly pointed to a late-2029 completion target. The tower’s redevelopment was enabled by the Midtown East rezoning and a City Planning Commission special permit that allowed additional floor area in exchange for transit upgrades, with those zoning documents filed at the City Planning Commission. With foundation work now visible, crews are expected to keep pushing on below-grade construction before moving into superstructure pours and vertical framing in the coming months.
For neighbors and commuters, the near-term forecast is more truck traffic, cranes and sidewalk detours, followed by a long-term reset of the Madison Avenue streetscape as a new, sustainability-focused office tower opens and plugs directly into Grand Central’s concourse. We will be watching for the next big milestones, including the opening of the MTA entrance and the first steel rising above street level, and will report back as the tower climbs into the skyline.
