Rust does well on this front. There's a new release every 6 weeks, and majority of users jump on it straight away (to complete shock of everyone not used to it).

Rust has editions which keep old code working without any changes, even if you mix it with new code, even if you do it with macros. It has rustfix that automatically migrates majority of the old code.

Rust has a standard project layout, standard test runner, and a central code repository, which enables testing language releases against nearly all publicly available code (see "crater run").

The language itself is stricter, with the safe subset being free of UB, so there's less stuff to break to begin with. You can't suddenly use a moved-from object.

There's even "cap lints" feature that disables `-Werror` equivalent for dependencies, so that new lints don't break your builds.