The Chicago Bears technically have until tomorrow (8/30) to get down to the mandated 75 player roster limit, but they have already started trimming their roster. I never understood the point of a going 90 to 75 when teams rarely play their starters in that final preseason game. Last year the Bears sat 30 of their 75 players for the preseason finale against the Cleveland Browns, and I would imagine they do something similar this Thursday night.
The Bears, like most teams, already know 95% of the players they plan to open the 2016 season with. Injuries could throw a wrench into things, but for the most part, there are only a couple of players legitimately fighting for a shot on an opening day roster.