It’s the SDK, but his original statement is correct. The info is out there publicly if you look at the right place.
These are the patch notes for the initial SU10 beta release which include the majority of changes. If you look at the notes for the subsequent beta releases, you’ll see the same, albeit much shorter lists.
It’s not yet 1 concise list, but that will come with the release of SU10.
https://forums.flightsimulator.com/t/sim-update-10-beta-release-notes-1-27-9-0/528823