The current tech boom started around 2011-2012, and a lot of companies signed multi-year leases around that time. My company leased an office for 5 years in 2012, and our lease will expire in early 2017. We expect the price to increase substantially, and we are considering moving the office to save some money.

I suspect a lot of 5-year leases are going to be ending this year, and a lot of companies will be looking for new space. If Twitter might as well get a piece of the action, if they aren't using that part of their building.