Today, Samsung started rolling out Galaxy S9 Pie update on a wider basis. That means most of the S9 users will receive the update. All but one thing is pretty new in this update, which makes the update special for the time being.
Yes, the update also brings January Security Patch as well, making the software version higher than those present in the market currently.
The update brings the firmware to the version XXU2CRLN, which is pretty newer than that currently present in the market, i.e XXU2CRLI. Also, you will get the One UI along with the Galaxy S9 Pie update.
For now, Samsung is rolling out the update as OTA, whereas the Galaxy S9+ can try updating with Smart Switch. It may take some time for the update to reach your device. Have Patience!
My Galaxy A6+ is still stuck on October Security Patch, Unfortunately ;_;