diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
new file mode 100644
index 0000000..2de3629
--- /dev/null
+++ b/.github/workflows/tests.yml
@@ -0,0 +1,106 @@
+name: tests (CPU)
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    name: Python ${{ matrix.python-version }}
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.12", "3.13", "3.14"]
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+          cache: pip
+
+      - name: Show environment
+        run: |
+          python --version
+          pip --version
+
+      - name: Install package
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[safetensors]"
+
+      - name: Show resolved dependencies
+        run: pip list
+
+      - name: Verify package imports
+        run: python -c "import aether as ae; print('aether from', ae.__file__)"
+
+      - name: Verify lazy namespace resolves
+        run: |
+          python - <<'PY'
+          import aether as ae
+
+          names = [
+              "Model",
+              "Conv2d", "Dense", "BatchNorm",
+              "MaxPool2d", "AvgPool2d", "GlobalAvgPool",
+              "Dropout", "SpatialDropout",
+              "ReLU", "LeakyReLU",
+              "AdamW",
+              "SoftmaxCategoricalCrossEntropy",
+              "CategoricalAccuracy", "RegressionAccuracy",
+              "Compose", "Rescale", "StandardScaler", "ToTensor",
+              "to_tensor",
+          ]
+
+          missing = [n for n in names if not hasattr(ae, n)]
+          if missing:
+              raise SystemExit(f"lazy namespace failed to resolve: {missing}")
+          print(f"resolved {len(names)} public symbols")
+          PY
+
+      - name: Verify required dependencies are declared
+        run: |
+          python - <<'PY'
+          import importlib.util
+
+          for pkg in ("numpy", "safetensors"):
+              if importlib.util.find_spec(pkg) is None:
+                  raise SystemExit(
+                      f"{pkg} not installed - it is used by the test suite "
+                      f"but missing from pyproject.toml dependencies"
+                  )
+          print("numpy and safetensors present")
+          PY
+
+      - name: Confirm runner has no GPU backend
+        run: |
+          python - <<'PY'
+          import importlib.util
+
+          if importlib.util.find_spec("cupy") is not None:
+              raise SystemExit(
+                  "CuPy is installed on a CPU-only runner - this workflow "
+                  "would report coverage it cannot actually verify"
+              )
+          print("CuPy absent - GPU tests will be skipped")
+          PY
+
+      - name: Run test suite
+        run: python -m unittest discover -s tests -v
\ No newline at end of file
diff --git a/pyproject.toml b/pyproject.toml
index 7f9bc42..f8855f2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,14 +5,26 @@ build-backend = "setuptools.build_meta"
 [project]
 name = "aether-ml"
 version = "0.1.0"
-requires-python  = ">= 3.14"
+requires-python  = ">= 3.12"
 dependencies = [
     "numpy", 
 ]
 
 [project.optional-dependencies]
+safetensors = ["safetensors>=0.8.0"]
 gpu-nvidia = ["cupy-cuda12x"]   # CuPy wheel from PyPI
-gpu-amd = []                    # CuPy compiled inside aether-rocm.Dockerfile
+gpu-amd = []                    # CuPy compiled via ROCm container env
+
+notebooks = [
+    "safetensors>=0.8.0",
+    "jupyterlab",
+    "matplotlib",
+]
+
+dev = [
+    "aether-ml[safetensors]",
+    "aether-ml[notebooks]",
+]
 
 [tool.setuptools.packages.find]
 where = ["."]