Websites have started showing "Yosemite" compatibility
Yosemite until finally release on http://www.apple.com/pr/ is pure speculation, and hence not really able to be discussed on this forum.
Beta for lack of a better word means guinea pig software. Anyone who has it is under nondisclosure to discuss it.
Yet places such as http://www.roaringapps.com/ clearly show attempts to show new software compatible with it, and iOS 8, which is also a Beta.
Take any such software reports for a software that is in beta with large grain of salt in terms of compatibility until after release, and make sure those reports are updated after the release date. And remember if you need a new computer to read this tip:
https://discussions.apple.com/docs/DOC-2294
And backup your data before installing anything new.