What does it mean for Swift to be ABI stable? ABI stands for application binary interface. ABI stability was introduced in Swift 5 and it means that the binary interface of the language is guaranteed to remain stable across different versions of the compiler and platforms.

Does this sound confusing? Let me put it differently. As of Swift 5, libraries, frameworks, and executables compiled with version A of the compiler can be used with version B of the compiler. The only requirement is that they were compiled against the same ABI.

What Does This Mean for Swift?

As of Swift 5, the code you compile has a stable binary interface, which means that it is compatible with future versions of the language. The benefit is that it is much easier to work with libraries and frameworks. You no longer need to make sure that the Swift version of the library or framework your project uses matches the project's Swift version.

What Is an Application Binary Interface?

If you are still confused, then understanding the concept of an application binary interface might be helpful to understand the importance of ABI stability. As the name suggests, an ABI is an interface. The interface is used by binaries (binary program modules), such as a library and a client using the library, to interact or communicate with one another.

The interface defines everything that is needed for the binaries to interact or communicate, for example, the layout of data structures in memory and the calling conventions for functions.


While ABI stability doesn't impact the code you write, it has an important impact on your day to day development. It ensures that the compiled products, such as libraries, frameworks, and executables, can interact with one another, regardless of the version of the compiler that was used to create them.