The best news--or the least surprising news, given the exceptionally constrained supply of office space?
Colliers says the current vacancy rate it measures for the aggregated Downtown markets (Back Bay/DTX/Seaport, etc.), of 7.9%, is at an 18-year low:
https://www2.colliers.com/en/Research/Boston/2019-Q3-Market-Viewpoint-Report-Boston-Colliers
What is interesting, though, is that now you have 3 towers rising/planned, each within 350 yards of each other:
Winthrop Center Tower: 772,000 sf office space. opening 2022
South Station Tower: 768,000 sf office space. opening ? (but construction underway)
125 Lincoln Street: 625,000 sf office space. BPDA review ongoing.
Obviously WCT gets to market first--in the best of all worlds, though, the openings are staggered (assuming 125 Lincoln gets approved) in such a way that there isn't a market glut of 2.2 million sf...