Even the C ABI many talk about, most of them don't have any idea of what they are actually talking about.
First of all, it is the OS ABI, in operating systems that happened to be written in C.
Secondly, even C binary libraries have plenty of breakage opportunities within the same std, and compiler.
ABI stability even in languages that kind of promise it, is in reality an half promise.
Bytecode, or some part of the language is guaranteed to be stable, while being tied to a specific version, not all build flags fall under the promise, and not much is promised over the standard library.
Even other good examples that go to great efforts like Java, .NET or Swift, aren't fully ABI safe.
It may be per-OS (I wouldn't try linking Linux and NT object files even if they were both compiled from C by GCC with matching versions and everything), but enough details come from C that I think it's fair to call it a C ABI. Like, I can write unix software in pascal, but in order to write to stdout that code is gonna have to convert pascal strings into C strings. OTOH, pascal binaries using pascal libraries can use pascal semantics even on an OS that uses C ABIs.
Try to link two binary libraries in Linux, both compiled with GCC, while not using exactly the same compiler flags, or the same data padding, for example things like structures.
Since committee people can explain it even better,
"To Save C, We Must Save ABI"
https://thephd.dev/to-save-c-we-must-save-abi-fixing-c-funct...
And while, yes, there are times where ABIs are broken, compiler versions affecting things would add a whole another uncontrollable axis on top of that. I would quite like to avoid a world of "this library can only be used by code compiled with clang-25" as much as possible.
