I’ve been searching rather diligently, but I cannot seem to find anywhere that describes how one knows if one has the new FSD Beta build?
If you had the beta you would know. Especially since you would have signed a legally binding NDA. There are also numerous visible differences between the beta and general public releases.
TeslaScope was tracking the beta versions for a while but last I checked they removed them. Possibly at request of Tesla?
The beta versions keep changing. There has been several now. Something like 6 or 8 so far I think?
EDIT: Tesla Software Updates actually lists all the beta versions.
(Just search for "Full Self-Driving (Beta)")