2016 (late 2015 build). Had a leaking valve replaced this past November, I think near the heater core. They drained some (maybe most) coolant for the repair. Low warning light came on a week later so we went back and had it topped up. Light has come back on 2 days ago. Progressed from "pull over safely" to "stop driving" or something along those lines. No obvious leaks I can see, no puddles in the garage, and there's a small amount of coolant left in the overflow tank. I do live somewhere that gets cold during winter, but it was fairly cold when this repair & last top up were done (though not quite this cold)
Don't believe the manual states an aftermarket equivalent coolant to use. I'd like to top it off again and see if it drops again (meaning a leak). Would prefer not to drive 30 minutes back to the dealer until I know what's going on, if anything. Parts websites show a number of compatible coolants, but I don't trust it (there's a mix of standard, OAT, HOAT etc. being shown). What's in the tank now is green. I suppose I could add some distilled water for time being as I doubt it'll affect the freezing point much at all. Usually 20-30 degrees F here during winter, sometimes down around 0 degrees F.