I think the RS3 ARB should fit all since the support frame are the same for all.. But according to ETKA, it's the same 21.7mm as the S3s, only 3.6mm wall thickness instead of 3mm. Doubt it's worth the money for the upgrade and the reason I went with H&R, the H&R is 25mm and solid..
My original plan was 034Motorsports thinking it's 22.2mm would be better suit for rear sway only upgrade, but the shipping costing more than the sway itself to Hong Kong, I gave up.. 25mm H&R seems a little drastic for rear only application, it's almost twice as stiff as the stock but I'm glad I went with H&R at the end, it turn in and handles beautifully for the way I drive at least...
And you guys seen the RS3 Sedan's testing video right?? I bet it has the same 21.7x3.6 ARB and TBH, I wouldn't want that ARB with all those Mermaids and Unicorns seen in the video... And this is RS3 with better suspensions and Haldex! There was another video where the RS3 was being chased by a W213 E63, and the E63 caught up with the RS3 in just a turn or two (NOT STRAIGHT), again... too many Mermaids and Unicorns in the video...