Does OpenUSD support defining animation blends

Does OpenUSD have a way to define things like blend trees, transitions between animations or anim state machines?

Do blend shapes allow referencing multiple tracks and blending them based on a user defined variable?

It seems like it doesn’t based on this article

That is correct. You can achieve animation retiming using Value Clips, but no blending or recombination of animation clips. That is a feature that could be supported within the context of OpenExec, but not before then.