go.mod provides a way to introduce the new behaviour incrementally. The key point is the dependencies can (and already do) declare different go versions in thei

go.mod provides a way to introduce the new behaviour incrementally. The key point is the dependencies can (and already do) declare different go versions in their go.mod file. When everything is compiled, each module is compiled with the behaviour that applies to its own declared go version. So even if you update your go.mod go version to take advantage of this (soon to be) new behaviour, you can continue to use existing deps happily without worrying they will break.