Like fuel, it appears they don't ship with a full tank. My dealer made a point of telling me they had to make sure it was topped off. My co-worker with a 2016 had to put fluid in his at 1500 miles (I have 4200 and it still says OK).
I added 2.5 gallons at 3900 miles. I figured it should have been enough when purchased new to get me to my first service. As stated above, it may have been only partially filled. I'll see how it goes after my first official free maintenance.
Mine said it would be out in 900 miles 22% when I had 1,000 miles on it, probably not filled by the dealer. Dealer said schedule fill up and it would be free during warranty. Decided my time was worth more and bought 2.5 gal. from dealer for $25, drove on a 2,000 mile trip and it's down to 26% again! At this rate it adds about $.125 per mile to the diesel cost, which by the way here in CA, the diesel at Costco has gone from $2.30 a gallon to about $2.60 last time I filled up, now $2.79, there goes the cost per gallon advantage with diesel! Ant 1.5-2 cents per gallon for DEF.