Module of this kind sometimes provide a function that indicates which version was loaded. That does not appear to the be the case here.

Module of this kind usually split the PP and XS components into different modules. For these, you could test %INC for the XS version of the module. That's not the case here.

So that leaves checking if the binary component of the module was loaded.

use DynaLoader qw( );
use XML::Easy  qw( );

warn "You may experience poor performance due to "
   . "the use of a Pure Perl build of XML-Easy.\n"
      if !grep $_ eq 'XML::Easy', @DynaLoader::dl_modules;
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