How do I differentiate traffic from a website and its AMP version if they're tagged the same way?

If they're tagged identically, pages loaded from a website and its AMP version will not be distinguishable in our interfaces.

However, it is possible to add specific tagging to your AMP pages' tags so that they can be differentiated.

We recommend you to declare a custom property typed as a boolean. For example : 

"Is AMP?": True / False

You will find the documentation linked to set a custom property. 

In the analysis will have the possibility to filter on "Is AMP?" with the values “True” or “False” to differentiate the traffic.