Are Promises unicast or broadcast?

Question

This book says Promises are unicast, while this one says they are broadcast.

Answer 1

The sentence

With Observable sequences, you get that behavior for free in a multicast behavior, instead of the unicast Promise behavior.

is inaccurate. It seems to refer to the fact that an observable can fire a callback multiple time while a promise fires its callbacks only (at most) once. However, that's not the standard meaning of unicast/broadcast, which is about the number of receivers - of which both promises and observables can have any.