When was the latest Rust stable release - every 6 weeks - that did not change the "spec" at all, e.g., by adding new stable features or standard library APIs ?

It is true that on a six-week basis we add new things. I should have been more specific, haha. The point is that the language does not make daily breaking changes, which is a reputation that we still sometimes have even after all of these years of no longer doing so.

That said, you are still right that it is a thing that the gcc-rust developers will need to keep up with.

In any case, one could consider the Rust epochs as main synchronization points anyway.

I would not, because new things land in most editions, so it’s not like a particular edition refers to a stable subset of the whole language.

True, however with the enterprise hat I see epochs as LTS versions worthy to be the ones on CI/CD pipeline.

I think LTS versions are great, but see them as something very distinct from editions. It is something I would like to see us have eventually.