FWIW, the article says "Frontends are somewhat insulated from this because they can use the largely stable C API." but that's not been my/our experience. There are parts of the API that are somewhat stable, but other parts (e.g. Orc) that change wildly.
FWIW eventual stability is a goal, but there's going to be more churn as we work towards full arbitrary program execution (https://www.youtube.com/watch?v=qgtA-bWC_vM covers some recent progress).
If you're looking for stability in practice: the ORC LLJIT API is your best bet at the moment (or sticking to MCJIT until it's removed).
Yes, the Orc C API follows different rules from the rest of the C API (https://github.com/llvm/llvm-project/blob/501416a755d1b85ca1...).