[zahlman]

The concept of NaN long predates the language that uses ===, and is part of a language-agnostic standard that doesn't consider other data types. Any language choosing to treat the equality (regardless of the operator symbol) of NaN differently would be deviating from the spec.

[freehorse]

Julia evaluates NaN === NaN to true, as long as the underlying bit representations are the same. Eg NaN === -NaN evaluates to false, as happens also with NaNs where for some reason you tinker with their bytes. I think it makes sense that it is so though, regardless that I cannot think of any actual use cases out of doing weird stuff.