The 5cyl RS3 engine does not require “breaking in”. The same goes for versions 8 and 10. It’s the same with Porsche engines, which are evaluated and broken in before the car ever leaves the factory. So yeah, I’m surprised how many people still don’t know this…
The motors are there, but how about the drivetrain? Giving the transmission and rear differential some proper heat cycles before smashing them appears smart.
I’m pretty sure my friend had it coded in his RS7; the revs were limited until break-in, and I’m not sure what the needed mileage was. I didn’t have it in my S3, so I’m not sure how it works with RS3.
Although dealers may recommend break-in, the OP should maintain a maximum RPM of 2500-3000 for the first 1500-3000 km (~1000-2000 mi), then perform the first oil change and enjoy the car. Take care of your engine, bro… it’s a good one; with break-in and frequent oil changes, it should last a long time!