Yes, V8 uses the least significant bit to distinguish Smis from heap object pointers. That applies to all JS values, so that's why I've mentioned this special case in context of Maps/Sets.

Franziska Hinkelmann wrote a nice blog post on Smis: https://medium.com/fhinkel/v8-internals-how-small-is-a-small-integer-e0badc18b6da

They're also covered in V8 team's post on pointer compression feature: https://v8.dev/blog/pointer-compression