Yes, I am very aware about how often I share a link to this Page, what makes it kinda non-secret. The only way to find this, aside from me telling it in some random Chat, is by reading the Changelog of GT6, where it is mentioned at the very bottom of the Page.
This Version is exclusively for Testing purposes and absolutely UNPLAYABLE, the Download yields whatever work in progress I have, which might be very savegame breaking or even crashing on startup. Please wait for the official Releases, that should be less than a week of waiting. Do not report Bugs inside this Version unless I explicitely ask you personally to do so. I usually didn’t even test that Version myself as it gets uploaded the same moment I drop it into my Mods Folder to start MC.