After pretty much every carrier version of the device has already received the update, owners of unlocked Samsung Galaxy S9 phones are reporting that Android 9 Pie has started to grace their units. The hefty 1.7-gigabyte update also brings with it Samsung's updated One UI as well as the January Android security patch.
Conventional Android wisdom holds that carriers often delay OS updates, but that certainly hasn't been the case here — Xfinity, T-Mobile, Verizon, Sprint, AT&T, and US Cellular versions of the S9 and S9+ have all already seen the Pie update.
You know the drill: the update should occur automatically, but if it hasn't yet and you're really eager, you can head to Settings > Software update > Download updates manually to initiate it yourself. We haven't yet heard of the update hitting the unlocked S9+, but if carrier versions are anything to go by, it'll happen sooner than later.