The 2018 MLS season isn’t over and won’t be over for another two weeks, but the off-season will begin on Monday.
By 1:00 pm on November 26, the clubs that aren’t still in the playoffs - i.e. all the teams in MLS except Atlanta United, New York Red Bulls, Portland Timbers, and Sporting Kansas City (and 2019 expansion club FC Cincinnati, which doesn’t really have a roster to purge yet) - must notify the league office of the contract options they will be exercising and those players on expiring contracts who have received bona fide offers to renew.