> I forget if stability was introduced in 4.x or 5.x, but code written today should be fine... They've always provided source compatibility modes in new releas

> I forget if stability was introduced in 4.x or 5.x, but code written today should be fine... They've always provided source compatibility modes in new releases of the compiler so you can delay making syntax changes to an existing codebase if you need to. You're thinking of ABI stability, which is in place as of Swift 5, and doesn't have anything to do with what parent is talking about.