Rate goes down, and your interest payment goes down.
I suspect this has to do with fact that there has never been a rate decrease in the lifetime of the product:
> Wealthfront Inc. is an automated investment service firm based in Redwood City, California,[2][3][4][5] founded by Andy Rachleff and Dan Carroll in 2008
https://en.wikipedia.org/wiki/Wealthfront
The decrease came only as a surprise to those who weren't paying attention.
The rate is in all likelihood headed to zero and below, just like so many other industrialized economies have already done.
If that comes as a surprise then once again, you haven't been paying attention.