diff --git a/.github/workflows/test_actions.yml b/.github/workflows/test_actions.yml
index 4127ebb..a8d4d3e 100644
--- a/.github/workflows/test_actions.yml
+++ b/.github/workflows/test_actions.yml
@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest, ubuntu-latest]
-        python-version: [3.9, '3.10', 3.11, 3.12, 3.13]
+        python-version: [3.9, '3.10', 3.11, 3.12, 3.13, 3.13t, pypy3.10, pypy3.11]
     steps:
       - name: Check out repo
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
@@ -21,12 +21,22 @@ jobs:
           python-version: ${{ matrix.python-version }}
       - name: Check Python version
         run: |
-          import sys
+          import sys, sysconfig
           version = sys.version_info[:2]
-          expected_version = tuple(map(int, "${{ matrix.python-version }}".split(".")))
+          expected_version = tuple(map(int, "${{ matrix.python-version }}".removeprefix("pypy").removesuffix("t").split(".")))
           if version != expected_version:
               print(f"::error title=Test Failure::The Python version does not match. Got {version}, expected {expected_version}.")
               sys.exit(1)
+          implementation = sys.implementation.name
+          expected_implementation = "pypy" if "${{ matrix.python-version }}".startswith("pypy") else "cpython"
+          if implementation != expected_implementation:
+              print(f"::error title=Test Failure::The Python implementation does not match. Got {implementation}, expected {expected_implementation}.")
+              sys.exit(1)
+          threading = "free-threading" if sysconfig.get_config_var("Py_GIL_DISABLED") else "GIL"
+          expected_threading = "free-threading" if "${{ matrix.python-version }}".endswith("t") else "GIL"
+          if threading != expected_threading:
+              print(f"::error title=Test Failure::The Python threading does not match. Got {threading}, expected {expected_threading}.")
+              sys.exit(1)
         shell: python
 
   test_setup_poetry:
@@ -35,7 +45,7 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest, ubuntu-latest]
-        python-version: [3.9, '3.10', 3.11, 3.12, 3.13]
+        python-version: [3.9, '3.10', 3.11, 3.12, 3.13, pypy3.10, pypy3.11]
     steps:
       - name: Check out repo
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
@@ -62,7 +72,7 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest, ubuntu-latest]
-        python-version: [3.9, '3.10', 3.11, 3.12, 3.13]
+        python-version: [3.9, '3.10', 3.11, 3.12, 3.13, pypy3.10, pypy3.11]
     steps:
       - name: Check out repo
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
@@ -94,7 +104,7 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest, ubuntu-latest]
-        python-version: [3.9, '3.10', 3.11, 3.12, 3.13]
+        python-version: [3.9, '3.10', 3.11, 3.12, 3.13, pypy3.10, pypy3.11]
     steps:
       - name: Check out repo
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
diff --git a/README.md b/README.md
index a4af285..3fa3501 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,8 @@
     - [Outputs](#outputs)
       - [`python-version`](#python-version-1)
       - [`python-path`](#python-path)
+    - [Environment Variables](#environment-variables)
+      - [`pythonVersion`](#pythonversion)
   - [`ni/python-actions/setup-poetry`](#nipython-actionssetup-poetry)
     - [Usage](#usage-1)
     - [Inputs](#inputs-1)
@@ -82,6 +84,12 @@ steps:
     key: venv-${{ runner.os }}-py${{ steps.setup-python.outputs.python-version }}-${{ hashFiles('poetry.lock') }}
 ```
 
+`python-version` is unique across implementations (CPython vs. PyPy) and free-threaded builds:
+
+- CPython: "3.13.4".
+- CPython with free-threading: "3.13.4t"
+- PyPy: "pypy3.11.11-v7.3.19"
+
 #### `python-path`
 
 `actions/setup-python` sets the `pythonLocation` environment variable to the **directory**
@@ -96,6 +104,13 @@ steps:
 - run: pipx install <package> --python ${{ steps.setup-python.outputs.python-version }}
 ```
 
+### Environment Variables
+
+#### `pythonVersion`
+
+This is the same as `outputs.python-version` and is mainly intended for use in
+`ni/python-actions/setup-poetry`.
+
 ## `ni/python-actions/setup-poetry`
 
 The `setup-poetry` action installs Poetry, adds it to the PATH, and caches it to speed up
diff --git a/setup-poetry/action.yml b/setup-poetry/action.yml
index 379fb67..5664398 100644
--- a/setup-poetry/action.yml
+++ b/setup-poetry/action.yml
@@ -17,14 +17,12 @@ outputs:
 runs:
   using: composite
   steps:
-    - name: Get Python version
-      id: get-python-version
+    - name: Check that setup-python was called
       run: |
-        if [ ! -d "$pythonLocation" ]; then
+        if [ ! -d "$pythonLocation" -o -z "$pythonVersion" ]; then
           echo "You must use the setup-python action before using this action."
           exit 1
         fi 
-        "$pythonLocation/python" -c "import platform; print(f'python-version={platform.python_version()}')" >> "$GITHUB_OUTPUT"
       shell: bash
     - name: Set paths (Linux/Mac)
       if: runner.os != 'Windows'
@@ -57,11 +55,11 @@ runs:
         path: |
           ${{ steps.copy-paths.outputs.poetry-bin-dir }}/poetry*
           ${{ steps.copy-paths.outputs.poetry-home }}          
-        key: poetry${{ inputs.poetry-version }}-${{ runner.os }}-py${{ steps.get-python-version.outputs.python-version }}
+        key: poetry${{ inputs.poetry-version }}-${{ runner.os }}-py${{ env.pythonVersion }}
     - name: Install Poetry
       if: steps.cache-poetry.outputs.cache-hit != 'true'
       run: |
-        "$pythonLocation/python" -m venv "$POETRY_HOME"
+        python -m venv "$POETRY_HOME"
         "$POETRY_HOME_BIN/python" -m pip install poetry==${{ inputs.poetry-version }}
         mkdir -p "$POETRY_BIN_DIR"
         ln -s "$POETRY_HOME_BIN/poetry"* "$POETRY_BIN_DIR/"
diff --git a/setup-python/action.yml b/setup-python/action.yml
index bda922d..3cee10b 100644
--- a/setup-python/action.yml
+++ b/setup-python/action.yml
@@ -7,7 +7,7 @@ outputs:
   python-path:
     value: ${{ steps.setup-python.outputs.python-path }}
   python-version:
-    value: ${{ steps.setup-python.outputs.python-version }}
+    value: ${{ steps.get-python-version.outputs.python-version }}
 runs:
   using: composite
   steps:
@@ -16,3 +16,22 @@ runs:
       id: setup-python
       with:
         python-version: ${{ inputs.python-version }}
+    # Workaround for https://github.com/actions/setup-python/issues/1109 -
+    # Python-version output for PyPy isn't unique across different versions 
+    - name: Get Python version
+      id: get-python-version
+      run: |
+        import os, platform, sys, sysconfig
+        if sys.implementation.name == "pypy":
+            version = f"pypy{platform.python_version()}-v{'.'.join(map(str,sys.implementation.version[:3]))}"
+        else:
+            version = platform.python_version()
+        # Also take free-threading into account
+        if sysconfig.get_config_var("Py_GIL_DISABLED"):
+            version += "t"
+        with open(os.environ["GITHUB_OUTPUT"], "a") as output:
+            print(f"python-version={version}", file=output)
+      shell: python
+    - name: Add pythonVersion environment variable
+      run: echo "pythonVersion=${{ steps.get-python-version.outputs.python-version }}" >> "$GITHUB_ENV"
+      shell: bash
\ No newline at end of file