IOS new versions and network load

Sun Sep 17 20:56:01 UTC 2017

A couple years ago, Apple unleashed an IOS update which made the news
because network operators reported serious congestion on their networks
as everyone and their uncle tried to download the gig+ package at 11:00 PDT.

Was the problem solved simply by Apple staggering the announcement of
downloads? or were there distribution network changes also made to
reduce the load?

In Canada, during net neutralirty hearings, it was revealed that
cellular carriers zero rated over the air updates.  I know my iPhone
gets updates without me asking for them, only getting a "update ready to
install" while on a long cycling ride (aka: must have used cellular data).

Does anyone know whether this is pushed by Apple who has gotten the OK
form individual carriers, or is it pushed by carriers (with Apple's OK)
in a low priorioty stream that doesn't cause congestion on cellular
network? (carriers delivering content in "push mode" would change their
role).