Carlos Vela will stay at Real Sociedad until January 2018. The Mexican player will then leave to play in the MLS, after an agreement between the league and the player, per La Real.
Vela, 28, still has a year left at Sociedad and a release fee of 10 million euros. However his unwillingness to renew means the club have decided the best thing to do is to sell him early, instead of letting him go for free at the end of that period.
Various clubs in Europe were interested in him, including Roma and Wolfsburg. But he has opted to go to the MLS. He is likely to play for Los Angeles FC according to American media. A club who are debuting in the MLS this year and will have Vela as their figurehead.
Because of the way the American league works, the league holds the contracts rather than the clubs - hence his destination is not yet official, but he will be playing in the States.