T-Mobile Simple Choice plan free upgrade from 2.5GB to 4GB YMMV

I recently login to my.t-mobile.com and check my current internet plan.
I currently have 2.5GB data for each line on Simple Choice plan.
I click "CHANGE DATA" and select 4GB data.
I got free upgrade from 2.5GB to 4GB for all the lines with no extra charge.
I call 611 and the rep confirms that is a promotion from 2.5GB to 4GB of data free of charge until Feb 2019.
https://my.t-mobile.com/plans.html
YMMV