Swift 6.3 ships

Swift 6.3 development snapshots were published starting with nightly toolchains announced on Dec 9, 2025, while the formal 6.3 release process was opened on Oct 24, 2025 as the release branch moved through CI and platform snapshot stages. (forums.swift.org) The Embedded Swift subset gained a pure‑Swift implementation of Float/Double description and debugDescription so floating‑point types can be printed from embedded stdlib builds without platform-specific shims. (swift.org) A new EmbeddedRestrictions diagnostic group was added and enabled by default when building Embedded Swift, with a compiler flag (-Wwarning EmbeddedRestrictions) and a SwiftPM swiftSettings example (.treatWarning("EmbeddedRestrictions", as:.warning)) for opting into the same checks in non‑embedded builds. (swift.org) Low‑level linkage controls from accepted proposals landed: SE‑0492 (@section and @used) was accepted with modifications in mid‑October 2025 to allow section placement and no‑dead‑strip behavior, and SE‑0497 (the @export attribute for defining client‑visible vs implementation symbols) completed review and was revised during October 2025 before acceptance. (forums.swift.org) Debugging and device tooling were expanded in 6.3 with Swift MMIO 0.1.x (includes svd2swift code generation and a SwiftPM plugin) plus an SVD2LLDB plugin for name‑based register inspection and ARMv7‑M exception unwinding that produces full backtraces through exception frames. (swift.org) Toolchain and ecosystem updates include Swift Package Manager notes showing a SwiftBuild preview in the SwiftPM 6.3 workstream, and platform efforts such as Android SDK nightly previews alongside explicit language compatibility guidance that a target written in Swift 6.3 can depend on modules built with Swift 5, 4.2, or 4. (github.com)