robertferanec , 05-20-2019, 07:40 AM
You can set differential pair classes in then new Altium (I do not know why they call it Diff. Pair Net Class, but what they mean is Diff Pair Class).
If you do not want to set them in schematic, then Project -> Project Option -> ECO generation. Find "Remove Differential Pair Classes" and set it to "Ignore Differences".