Boston Properties files $14.2M buildout at 360 Park Ave South

Boston Properties has filed a $14.2 million alteration permit for interior work spanning five floors at 360 Park Avenue South, the Midtown South office tower it manages near Union Square. DOB NOW job filing M01456207-I1, filed October 16, 2026 and now listed in Professional Certification QA Review, covers general construction tied to tenant interior alterations on floors 2 through 5, plus infrastructure work in the sub-cellar, basement, first floor and roof. The filing states no changes in use, egress or occupancy, meaning the building’s certificate of occupancy is unaffected.

Why it matters

The filed floor range lines up with where Boston Properties has already placed tenants this year. In a March 2026 release, BXP said it signed roughly 230,000 square feet of new and expansion leases at the 450,000 square foot tower, including a reported 92,000 square foot expansion by proprietary trading firm Optiver across floors 2 through 5, the identical span named in this permit. A landlord-funded buildout of that scope, filed for the same floors a tenant just expanded into, points to the space moving from signed lease to delivery. For brokers tracking Midtown South availability, that narrows the near-term block of ready-to-build space at 360 Park Avenue South and signals the building’s reported push past 90 percent leased is being backed by active construction, not just signed paper.

The numbers

The $14,248,548 figure is the initial filed construction cost on the DOB NOW record, before any amendments. It covers the full multi-floor scope rather than a single tenant’s suite, so it is not a per-floor or per-square-foot buildout cost. No lease document ties this specific permit to Optiver by name. The filing identifies the owner’s business as Boston Properties and classifies the work as an alteration, not new construction, consistent with a repositioning of existing office floors rather than ground-up work.

What’s next

The job remains in professional certification review rather than an active permit, so construction has not been confirmed to have started. The next marker to watch is a DOB NOW status change to an approved or permitted state, which would indicate crews are mobilizing. BXP’s next earnings call is the likeliest venue for an update on 360 Park Avenue South’s occupancy rate and any named tenant deliveries tied to these floors. More on the submarket at New York market coverage.