The Android Pie rollout for the Samsung Galaxy S9 and S9 Plus is all but complete. The only devices yet to receive the update were the carrier-unlocked variants of the device. That changes today, as the carrier-unlocked models in the US are finally beginning to receive their Android Pie update. Historically, carrier-unlocked devices in the US have always been the last to receive a major software upgrade, and things don't look any different this time either.
The OneUI-based Android Pie update weighs in at nearly 1.8GB and comes with the January 2019 security patch. One would expect it to come with the February security patch, considering that it is already available for other variants of the Galaxy S9. The software version for the S9 and S9+ updates is G960U1UEU3CSA8 and G965U1UEU3CSA8 respectively.
The update is being rolled out in batches and may not be available for download immediately. Ideally, you should get a notification about it once your device detects that there is an update available. If you want to trigger it manually, then head over to Settings » Software update and select the 'Download Update Manually" option.
Now that the update is ready for the Galaxy S9+, the Galaxy Note 9 shouldn't be too far off. We can expect it to hit the airwaves in the next few days. Now that all variants of the Galaxy S9 are Pie-ready, it is time for their predecessors to get the update. The Galaxy Note 8 has already received it in some markets, and we can expect a global rollout in the coming weeks. Carrier-unlocked devices, however, still will have to wait for around a month before they can get a piece of the Pie.