After Googling I can see links to this:
Which seems legitimate given the domain, but its an old version (Revision 6 circa 2016) and there are plenty of websites and documents that now reference Revision 7 (circa 2018 Doc ID: 07-5123-07).
I can only find download links for Revision 7 from Chinese cdn websites that want you to download their software first (err no thanks!)
I also can't seem to find any links from within the Zigbee Alliance's website menu (would have thought it would be in the "Developer Resources") - and I'm not quite prepared to stump up $7k for an "Adopter" membership just yet.
Am I missing something ?