In other words, only by starting construction of this building--which was introduced to the public in September 2015 as 615 Dean and is among three sites for sale--could developers Greenland Forest City Partners preserve a lucrative tax break.
But what does starting construction--a common tactic for developers-- mean? As stated in the 421-a law: "'commence' shall mean the date upon which excavation and construction of initial footings and foundations lawfully begins in good faith."
The building does have permits, granted in September 2015, for foundation work and support of excavation work, among others. But, as shown in the photos below, the work looks mostly like pretty general excavation.
Unless the footings--precursors to foundations, "typically made of concrete with rebar reinforcement that has been poured into an excavated trench"--are those very few vertical "knobs" at the north end of the first photo, or those partly buried white horizontal lines, they're tough to see.
Update: Here's what's going on at the site, according to the latest Construction Update: "Site preparation and removals of any above grade structures within the site, stripping of asphalt, and general excavation and removal of top layer of material will continue during this period."