Chris Lattner — already known for creating LLVM, the compiler infrastructure much of the industry now depends on — began designing Swift in July 2010 as a personal project inside Apple, later joined by a small team; the language stayed largely secret until Apple unveiled it publicly at WWDC in June 2014. Swift was built explicitly to replace Objective-C, addressing its well-known safety gaps (manual memory management footguns, weak type safety) while remaining fully interoperable with the vast existing Objective-C codebase and libraries Apple's platforms depend on. Apple open-sourced Swift in December 2015, and it now runs on Linux and Windows in addition to Apple's own platforms.
Hello, World — minimal, no semicolons required
Swift needs no class wrapper for a simple script and no semicolons at line ends, though they're legal if written — a deliberately lighter syntax than Objective-C's.
print("Hello, World!")Designed to replace Objective-C, without breaking it
Swift and Objective-C can call each other directly within the same project — this bidirectional interop was essential, since Apple's own platform frameworks (UIKit, Foundation) were originally written in Objective-C and Apple needed existing apps to adopt Swift incrementally, not all at once.
Swift 6 (2024): strict concurrency checking, opt-in via language mode
Swift 6's headline feature made data-race safety checking available as a compile-time check — code that opts into the Swift 6 LANGUAGE MODE and accesses shared mutable state unsafely across concurrent tasks now fails to COMPILE, not just occasionally crashes at runtime. This is opt-in, not automatic: Apple's own migration guidance is explicit that "your projects continue to build with their current language mode" after upgrading to a Swift 6 toolchain, and new projects still default to the Swift 5 language mode — strict checking only turns on once a project is explicitly switched to Swift 6 language mode. Swift 6.4 (September 2026), the current version, has focused specifically on reducing the ceremony that strict concurrency's annotations initially required, while keeping its safety guarantees intact.