If you ordering a customer order then it will take some time for the car to be built so it will be 2018. If its stock, even if you buy in 2018 its more likely to be a 2017 model, unless you wait until march or so when its more likely that the stock cars will then be 2018.
My custom order was confirmed 15Dec and will be delivered in endMarch (ohh the wait...), so I guess it will be a 2018 model - I can't see how it wouldn't be.