[somat]

2^61 guids is... 36 exabytes, if my napkin math is correct. when storing them in binary format(16 bytes each) if doing the javascript thing and storing them as strings... (shudders) I don't even want to think about it.

Anyhow that was my first thought when you mentioned 2^61 guids, where are you even going to put them? second thought, I don't think enumerating 2^61 guids is trivial, in fact, I suspect it would take longer than anyone would be willing to spend, and if you are not storing them why are you generating them?

And what even is a guid collision attack? it is not like they are a hash, and since they tend to be public identifiers it turns out despite their stated use to prevent collisions, you can't really use guids generated by others(if they wanted collisions they would straight up just copy yours) so you end up regenerating them anyway.