Add free threaded build

Author: zcbenz

.github/actions/test-linux/action.yml

@@ -9,15 +9,29 @@ inputs:
 runs:
   using: "composite"
   steps:
+    # FIXME: The distributed tests fail with free-threading Python.
+    - name: Check free-threading Python
+      id: is-free-threading
+      shell: bash
+      run: |
+        echo "::group::Check free-threading Python"
+        if python -VV 2>&1 | grep "free-threading"; then
+          echo "result=true" >> $GITHUB_OUTPUT
+        else
+          echo "result=false" >> $GITHUB_OUTPUT
+        fi
+        echo "::endgroup::"
+
     - name: Run MPI tests
+      if: ${{ steps.is-free-threading.outputs.result == 'false' }}
       shell: bash
       run: |
         echo "::group::MPI tests"
         mpirun --bind-to none --allow-run-as-root -host localhost:8 -np 8 python python/tests/mpi_test_distributed.py
         echo "::endgroup::"
 
     - name: Run distributed tests
-      if: ${{ inputs.has-gpu == 'false' }}
+      if: ${{ steps.is-free-threading.outputs.result == 'false' }}
       shell: bash
       run: |
         echo "::group::Distributed tests"

.github/workflows/nightly.yml

@@ -41,7 +41,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python_version: ["3.11", "3.12", "3.13", "3.14"]
+        python_version: ["3.11", "3.12", "3.13", "3.14", "3.14t"]
         runner:
           - ubuntu-22.04
           - ubuntu-22.04-arm
@@ -59,7 +59,7 @@ jobs:
     if: github.repository == 'ml-explore/mlx'
     strategy:
       matrix:
-        python-version: ["3.10", "3.13"]
+        python-version: ["3.10", "3.13", "3.14t"]
     runs-on: [self-hosted, macos]
     steps:
       - uses: actions/checkout@v6

.github/workflows/release.yml

@@ -47,7 +47,7 @@ jobs:
     if: github.repository == 'ml-explore/mlx'
     strategy:
       matrix:
-        python_version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        python_version: ["3.10", "3.11", "3.12", "3.13", "3.13t", "3.14", "3.14t"]
         arch: ['x86_64', 'aarch64']
     runs-on: ${{ matrix.arch == 'x86_64' && 'ubuntu-22.04' || 'ubuntu-22.04-arm' }}
     env:
@@ -83,7 +83,7 @@ jobs:
     if: github.repository == 'ml-explore/mlx'
     strategy:
       matrix:
-        python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
+        python-version: ["3.10", "3.11", "3.12", "3.13", "3.13t", "3.14", "3.14t"]
     runs-on: [self-hosted, macos]
     env:
       PYPI_RELEASE: 1

python/src/CMakeLists.txt

@@ -2,6 +2,7 @@ nanobind_add_module(
   core
   NB_STATIC
   STABLE_ABI
+  FREE_THREADED
   LTO
   NOMINSIZE
   NB_DOMAIN