Announcing Swift 6.3.1

[mishal_shah]

We are happy to announce the release of Swift 6.3.1.

Install Swift Toolchain

• Install via Swiftly
  swiftly install 6.3.1 or swiftly install latest
• Download toolchain directly from Install Swift | Swift.org
• Docker images will be available on hub.docker.com/_/swift soon (PR#21263)
• Xcode 26.4.1 contains Swift 6.3.1

Release Notes

• Swift
  • Fixed stack-allocation bugs in async functions that caused “freed pointer was not the last allocation” crashes, particularly in swift_asyncLet_finish. These long-standing issues became more frequent in Swift 6.2 and 6.3 due to optimizer improvements. PR#88389
• LLDB
  • Fixed lldb failing to find the bundled Python shared library when using the NoAsserts variant of the Windows toolchain. This previously prevented lldb from starting. PR#12696
  • Fixed lldb displaying an incorrect Python version in the error message shown when Python fails to load. PR#12697
• Swift Testing
  • Fixed a build error that can arise in the code emitted by #expect when the comment argument is not a string literal and there is another visible type named Comment which conflicts with the testing library's built-in type by that name. PR#1648