The Core Team isn't declaring ABI stability on Linux yet. Finalizing the ABI on Linux is less valuable in the server domain (one of the most active use cases for Swift on Linux) than the (say) iOS app domain since service executables are routinely built from source for deployment in that domain anyway. We also have new platform ports coming up — such as Swift on Windows — that are based on the Swift on Linux port and we want more of that platform bringup work to happen first — with more of the details of the ABI fully audited for those platforms — before finalizing them.