Release procedure

The LLVM project creates a new release twice a year following a fixed schedule. This page describes the libc++ procedure for that release.

Prepare the release

This is done by the libc++ developers.

It should be finished before the Release managers start branching the new release:

  • Make sure libcxx/docs/ReleaseNotes/<VERSION>.rst is up to date. Typically this file is updated when contributing patches. Still there might be some information added regarding the general improvements of larger projects.

  • Make sure the deprecated features on this page are up to date. Typically a new deprecated feature should be added to the release notes and this page. However this should be verified so removals won’t get forgotten.

  • Make sure the latest Unicode version is used. The C++ Standard refers to the Unicode Standard

    The Unicode Consortium. The Unicode Standard. Available from:

    Typically the Unicode Consortium has one release per year. The libc++ format library uses the Unicode Standard. Libc++ should be updated to the latest Unicode version. Updating means using the latest data files and, if needed, adapting the code to changes in the Unicode Standard.

  • Make sure all libc++ supported compilers in the CI are updated to their latest release.


This is done by the LLVM Release managers.

After branching for an LLVM release:

  1. Update _LIBCPP_VERSION in libcxx/include/__config

  2. Update the version number in libcxx/docs/

  3. Update _LIBCPPABI_VERSION in libcxxabi/include/cxxabi.h

  4. Update _LIBUNWIND_VERSION in libunwind/include/__libunwind_config.h

  5. Create a release notes file for the next release from the template

  6. Point to the new release notes file from libcxx/docs/ReleaseNotes.rst

Post branching

This is done by the libc++ developers.

After branching it takes a couple of days before the new LLVM ToT version is available on Once it is available the pre-commit CI can start using the new ToT version. In order to make sure patches can be backported to the release branch the oldest compiler is not removed yet.

The section Upcoming Deprecations and Removals is cleared by the release managers. Copy back the items that were in this section.

The items that need changing are marked with LLVM POST-BRANCH.

Post release

This is done by the libc++ developers.

Support for the ToT - 3 version is removed:

  • Search for LLVM RELEASE and address their comments

  • Search for test that have UNSUPPORTED or XFAIL for the no longer supported version

  • Search for TODO(LLVM-<ToT>) and address their comments