Samsung has now started rolling out One UI Beta update (Android 9.0 Pie) for Galaxy S9 and Galaxy S9+ in China. The One UI Beta program has already started in the US, Germany, Korea, Spain, France, Poland, and UK.
Now, only one country is remaining, India. Hopefully, Samsung will start the roll out soon.
The Software version is G9600ZCU3ZRKL and G9650ZCU3ZRKL for the Galaxy S9 and S9+ respectively. It has a big size, it is 1702.53 MB.
Once signed up for the Beta program, you can check for the update manually by heading into the Settings > Software updates > Download updates manually. This will allow the software to update and load the beta version.
The stable Android Pie update for the Galaxy S9 and Galaxy S9+ is expected to follow in January 2019.