diff --git a/.github/workflows/ci-gpu.yml b/.github/workflows/ci-gpu.yml
index e2345ef..4ae1cc5 100644
--- a/.github/workflows/ci-gpu.yml
+++ b/.github/workflows/ci-gpu.yml
@@ -59,15 +59,13 @@ jobs:
         run: |
           export DEBIAN_FRONTEND=noninteractive
           apt-get update
-          apt-get install -y git git-lfs gcc software-properties-common
-          add-apt-repository -y ppa:deadsnakes/ppa
-          apt-get update
-          apt-get install -y \
-            python${{ matrix.python-version }} \
-            python${{ matrix.python-version }}-venv \
-            python${{ matrix.python-version }}-dev
+          apt-get install -y git git-lfs gcc
           git lfs install
 
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+
       - uses: actions/checkout@v4
         with:
           lfs: true
@@ -78,7 +76,7 @@ jobs:
       - name: Install dependencies and run tests
         run: bash code/scripts/check_python_compat.sh
         env:
-          PYTHON_BIN: python${{ matrix.python-version }}
+          PYTHON_BIN: python
           MODE: train
           SKIP_TESTS: "0"
           REQUIRE_GPU: "1"
@@ -141,12 +139,13 @@ jobs:
         run: |
           export DEBIAN_FRONTEND=noninteractive
           apt-get update
-          apt-get install -y git git-lfs gcc software-properties-common
-          add-apt-repository -y ppa:deadsnakes/ppa
-          apt-get update
-          apt-get install -y python3.13 python3.13-venv python3.13-dev
+          apt-get install -y git git-lfs gcc
           git lfs install
 
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+
       - uses: actions/checkout@v4
         with:
           lfs: true
@@ -156,7 +155,7 @@ jobs:
 
       - name: Install Python dependencies
         run: |
-          python3.13 -m venv .venv_mid
+          python -m venv .venv_mid
           . .venv_mid/bin/activate
           python -m pip install --upgrade pip setuptools wheel
           # TODO: matrix by CUDA major version [cu12, cu13]
@@ -197,6 +196,7 @@ jobs:
   # Runs only after merge to main (not on PR branches) to conserve GPU quota.
   # ---------------------------------------------------------------------------
   multi-gpu-tests:
+    if: github.ref == 'refs/heads/main'
     needs: gpu-tests
     runs-on: linux-amd64-gpu-rtxpro6000-latest-2
     container:
diff --git a/.github/workflows/long-running-tests.yml b/.github/workflows/long-running-tests.yml
index e53579f..57ab817 100644
--- a/.github/workflows/long-running-tests.yml
+++ b/.github/workflows/long-running-tests.yml
@@ -99,19 +99,20 @@ jobs:
         run: |
           export DEBIAN_FRONTEND=noninteractive
           apt-get update
-          apt-get install -y git git-lfs gcc software-properties-common
-          add-apt-repository -y ppa:deadsnakes/ppa
-          apt-get update
-          apt-get install -y python${{ env.PYTHON_VERSION }} python${{ env.PYTHON_VERSION }}-venv python${{ env.PYTHON_VERSION }}-dev
+          apt-get install -y git git-lfs gcc
           git lfs install
 
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ env.PYTHON_VERSION }}
+
       - uses: actions/checkout@v4
         with:
           lfs: true
 
       - name: Install Python dependencies
         run: |
-          python${{ env.PYTHON_VERSION }} -m venv .venv
+          python -m venv .venv
           . .venv/bin/activate
           python -m pip install --upgrade pip setuptools wheel
           pip install -r code/requirements_public_inference.txt
@@ -156,19 +157,20 @@ jobs:
         run: |
           export DEBIAN_FRONTEND=noninteractive
           apt-get update
-          apt-get install -y git git-lfs gcc software-properties-common
-          add-apt-repository -y ppa:deadsnakes/ppa
-          apt-get update
-          apt-get install -y python${{ env.PYTHON_VERSION }} python${{ env.PYTHON_VERSION }}-venv python${{ env.PYTHON_VERSION }}-dev
+          apt-get install -y git git-lfs gcc
           git lfs install
 
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ env.PYTHON_VERSION }}
+
       - uses: actions/checkout@v4
         with:
           lfs: true
 
       - name: Install Python dependencies
         run: |
-          python${{ env.PYTHON_VERSION }} -m venv .venv
+          python -m venv .venv
           . .venv/bin/activate
           python -m pip install --upgrade pip setuptools wheel
           # TODO: matrix by CUDA major version [cu12, cu13]
@@ -238,19 +240,20 @@ jobs:
         run: |
           export DEBIAN_FRONTEND=noninteractive
           apt-get update
-          apt-get install -y git git-lfs gcc software-properties-common
-          add-apt-repository -y ppa:deadsnakes/ppa
-          apt-get update
-          apt-get install -y python${{ env.PYTHON_VERSION }} python${{ env.PYTHON_VERSION }}-venv python${{ env.PYTHON_VERSION }}-dev
+          apt-get install -y git git-lfs gcc
           git lfs install
 
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ env.PYTHON_VERSION }}
+
       - uses: actions/checkout@v4
         with:
           lfs: true
 
       - name: Install Python dependencies
         run: |
-          python${{ env.PYTHON_VERSION }} -m venv .venv
+          python -m venv .venv
           . .venv/bin/activate
           python -m pip install --upgrade pip setuptools wheel
           pip install -r code/requirements_public_inference.txt
@@ -294,19 +297,20 @@ jobs:
         run: |
           export DEBIAN_FRONTEND=noninteractive
           apt-get update
-          apt-get install -y git git-lfs gcc software-properties-common
-          add-apt-repository -y ppa:deadsnakes/ppa
-          apt-get update
-          apt-get install -y python${{ env.PYTHON_VERSION }} python${{ env.PYTHON_VERSION }}-venv python${{ env.PYTHON_VERSION }}-dev
+          apt-get install -y git git-lfs gcc
           git lfs install
 
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ env.PYTHON_VERSION }}
+
       - uses: actions/checkout@v4
         with:
           lfs: true
 
       - name: Install Python dependencies
         run: |
-          python${{ env.PYTHON_VERSION }} -m venv .venv
+          python -m venv .venv
           . .venv/bin/activate
           python -m pip install --upgrade pip setuptools wheel
           # TODO: matrix by CUDA major version [cu12, cu13]