The way they are using to route around the Go 1 compatibility promise is to gate these backwards incompatible changes on the value of the go directive in go.mod.
If it says 1.22 or later you get the new library behavior, otherwise you get the old one.
We'll see how well this ends up working in practice.
This mimics Perl's "use 5.x", although the latter is scoped per module. Perl's backward compatibility track record validates the soundness of this approach.
Perl can also selectively enable features, in a way not dissimilar to Python's "from _future_ import X", except the latter is about forward compatibility with a future default, whereas Perl is all about backwards compatibility as a sane default.
I guess Go does it at the mod consistent level because it needs a global view of features whereas Perl can dynamically alter itself (including its parser) live.
