We have very strong backwards compatibility guarantees. We do reserve the right to make soundness fixes, but they must be trivial to fix in user code. Otherwise, we don't break backwards compatibility. We have had one or two of those in the first year and a half of post-1.0 Rust, but virtually all code that did not hit one of those issues still compiles today. Newer iterations of the C standard have also introduced small backwards incompatibilities, it's just how the world works.

Our intention is to have that kind of long-term stability, yes, and we put a lot of work into making sure that it happens.