Swift 6.4 brings better interoperability, faster performance, and Swift Build by default

Apple has officially released Swift 6.4, marking another significant step forward in Apple's open-source programming language. Bundled with Xcode 27, the update prioritizes developer productivity with a suite of ergonomic refinements designed to reduce friction in daily workflows. Among the headline improvements is enhanced interoperability between Swift Testing and XCTest, allowing developers to migrate incrementally without rewriting entire test suites. The new release also introduces async support within defer statements, ensuring cleanup code runs reliably whether a function completes normally or throws an error.

Performance gains and platform expansion round out the major announcements. Foundation receives notable optimizations, with URL parsing reportedly running up to four times faster than before. The Swift SDK for Android advances with the new LTS NDK 30, streamlining build processes and removing the need for post-install scripts. Embedded Swift continues maturing with generalized existential type support and improved debugging metadata that keeps binary sizes compact while preserving crash diagnostics. Debug builds across Linux, Windows, and Darwin also shrink significantly as binary Swift modules are no longer embedded in debug artifacts.

The release further strengthens Swift's cross-platform ambitions with new documentation infrastructure: a dedicated Swift documentation site has launched alongside open-sourced standard library documentation content. C interoperability expands bidirectionally, allowing Swift functions to be exposed back to C codebases. With refined warning control via the @diagnose attribute and simplified OS availability checks using the new anyAppleOS syntax, Swift 6.4 targets the accumulated pain points that experienced developers encounter regularly. The language now aims to serve the full development stack, from mobile applications and cloud servers to embedded systems and web browsers.