Will Blender start allowing Anthropic to train on your art automatically unless you opt-out?
There's absolutely no precident for Blender Foundation sponsorships leading to such things... So no, they probably won't do that.
Only for the SaaS customers
No. You can read about what the various sponsorship levels entails here[1].
Blender already has ton of other Corporate Patron level sponsors, such as Netflix, Meta, Intel, BMW, Adobe and others.
[1]: https://fund.blender.org/corporate-memberships/