Not necessarily instantly, but our CD is fast enough that changes are in production 5-10 minutes after hitting master.

But what's more valuable is that our artifacts are tagged with the commit hash that produced them, which is then emitted with every log event, so you can go straight from a log event to a checked-out copy of every relevant bit of code for that service.

Admittedly this doesn't totally guarantee you won't ever have to worry about multiple monorepo revisions when you're debugging an interaction between services, but I haven't found this to come up very much in practise.

Edit: I should also clarify, a change to any internal library in our monorepo will cause all services that consume that library to be redeployed.