In the release notes, there is:

The new EJB client is mostly, but not fully, backward compatible with JBoss EAP 7.0.

This needs a bit of further explanation, I think, because it might create the impression that it won't fully allow you to invoke EJBs on EAP 7.0.

The EJB client from EAP 7.1 has full protocol-level backwards compatibility with EAP 7.0, which means you can use it to invoke beans on a 7.0 server. Obviously the thing that will not work is dynamic identity switching, but all other things will.

I think that the expression not fully backward compatible with JBoss EAP 7.0 is not the most accurate, it is rather not fully backward compatible with EJB client from EAP 7.0, meaning that client applications which were compiled with EJB client from 7.0 might not work without changes when switching its client dependencies to EJB client from EAP 7.1.