GHC 9.14.1-rc2 is now available

Zubin Duggal <[email protected]> Thu, 6 Nov 2025 21:42:19 +0530
Newsgroups	gmane.comp.lang.haskell.ghc.devel,gmane.comp.lang.haskell.glasgow.user,gmane.comp.lang.haskell.cafe
Message-ID	<xve4oauuqnjrro6rwvqgy4nmi5tuwd5jsxxodlh5skrxkthhre@bfp6irmkolzb>
The GHC developers are very pleased to announce the availability of the
second release candidate of GHC 9.14.1. Binary distributions, source
distributions, and documentation are available at [downloads.haskell.org][].

The changes from the first release candidate are:

* Bump the exceptions submodule to 0.10.11
* Bump the os-string submodule to 2.0.8
* Fix a driver regression causing an infinite loop with cyclic imports

GHC 9.14 will bring a number of new features and improvements, including:

* Significant improvements in specialisation:
    * The `SPECIALISE` pragma now allows use of type application syntax
    * The `SPECIALISE` pragma can be used to specialise for expression arguments
      as well as type arguments.
    * Specialisation is now considerably more reliable in the presence of
      `newtype`s

* Significant GHCi improvements including:
   * Correctness and performance improvements in the bytecode interpreter
   * Features in the GHCi debugger
   * Support for multiple home units in GHCi

* Implementation of the [Explicit Level Imports proposal][levels]

* `RequiredTypeArguments` can now be used in more contexts

* SSE/AVX2 support in the x86 native code generator backend 

* A major update of the Windows toolchain and improved compatibility with
   macOS Tahoe

* ... and many more

A full accounting of changes can be found in the [release notes][]. Given the
many specialisation improvements and their potential for regression, we would
very much appreciate testing and performance characterisation on downstream
workloads.

Note that while this release makes many improvements in the specialisation
optimisation, polymorphic specialisation will remain disabled by default in the
final release due to concern over regressions of the sort identified in
[#26329][T26329]. Users needing more aggressive specialisation can explicitly
enable this feature with the `-fpolymorphic-specialisation` flag. Depending
upon our experience with 9.14.1, we may enable this feature by default in a
later minor release.

We would like to thank the Zw3rk stake pool, Well-Typed, Mercury, Channable,
Tweag I/O, Serokell, SimSpace, the Haskell Foundation, and other anonymous
contributors whose on-going financial and in-kind support has facilitated GHC
maintenance and release management over the years. Finally, this release would
not have been possible without the hundreds of open-source contributors whose
work have made the Haskell ecosystem what it is today.

As always, do give this release a try and open a [ticket][] if you see
anything amiss.


[downloads.haskell.org]: https://downloads.haskell.org/ghc/9.14.1-rc2
[release notes]: https://downloads.haskell.org/ghc/9.14.1-rc2/docs/users_guide/9.14.1-notes.html
[ticket]: https://gitlab.haskell.org/ghc/homepage/-/issues/new
[macos]: https://gitlab.haskell.org/ghc/ghc/-/issues/26166
[T26329]: https://gitlab.haskell.org/ghc/ghc/-/issues/26329
[levels]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0682-explicit-level-imports.rst

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