The outgoing Polo GTI had mulitilink rear suspension, so not much of a stretch to think that the new one would too.
I’ve got a 2016 Polo GTI, so the outgoing model. Here’s my rear suspension; beam axle.

I was convinced that it (outgoing model) had multi-link, tried hard to push the wife towards a Polo GTI instead of the A1. She's ip for a Polo this time around.(it was my money being spent), so looked well into it. Should be in a courtesy Polo tomorrow night when the R goes in, so will see what is missing in the ride on a fixed beam axle, just in case current brochure is wrong.
If i'm lucky, Pulman Durham will have an up! GTI to look at.