Seems the freethreading requires an explicit opt-in.

Author: ionelmc

.github/workflows/github-actions.yml

@@ -1223,6 +1223,7 @@ jobs:
         CIBW_BUILD: '${{ matrix.cibw_build }}'
         CIBW_FREE_THREADED_SUPPORT: '${{ matrix.cibw_ft }}'
         CIBW_CONTAINER_ENGINE: "docker; create_args: --cap-add=SYS_PTRACE"
+        CIBW_ENABLE: cpython-freethreading
         CIBW_BUILD_VERBOSITY: '3'
         CIBW_TEST_REQUIRES: >
           tox

ci/templates/.github/workflows/github-actions.yml

@@ -97,6 +97,7 @@ jobs:
         CIBW_BUILD: '{{ '${{ matrix.cibw_build }}' }}'
         CIBW_FREE_THREADED_SUPPORT: '{{ '${{ matrix.cibw_ft }}' }}'
         CIBW_CONTAINER_ENGINE: "docker; create_args: --cap-add=SYS_PTRACE"
+        CIBW_ENABLE: cpython-freethreading
         CIBW_BUILD_VERBOSITY: '3'
         CIBW_TEST_REQUIRES: >
           tox