That's not reality for most large companies, even though it's the right mindset for most software libraries. Ex: A new legal requirement comes in, resulting in a mandate that fields X and Y for certain queries, that are being done all over the codebase, now have to be tokenized. This is a breaking and mandatory change, with no room to allow systems to stay behind, and expensive consequences.

In this case you'll have a very short transition, between all consumers updating their client code (possibly in a backwards compatible way) and the change in the implicated system being deployed, not the other way around.