@kensanata Thanks!

The most highly voted and accepted answer doesn't say anything about why a statically typed language like OCaml needs this, but a couple of the other answers do. It turns out it's only needed for polymorphic functions, but they use the same representation everywhere for simplicity. I might steal this idea.

https://ocaml.org/learn/tutorials/performance_and_profiling.html#The-representation-of-integers-tag-bits-heap-allocated-values