Next year.....Sometime in 2019...Exact date unknown.
However it has just been reported that Tesla hit 200,000 in Q3 so the full $7500 tax credit expires Dec 31, 2018. Then drops to $3750, then $1875.
So you may want to weigh that against the cost of SAS.....basically having to add your Qtrs Tax Credit to the cost of SAS.
Ski