diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0b00f3c6..1a9efe72 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -127,7 +127,7 @@ jobs:
         run: python -m pip install -e .[dev]
 
       - name: Install awkward v2
-        run: python -m pip install -U awkward numpy
+        run: python -m pip install -U awkward "numpy<2.1"
 
       - name: Run doctests on Python 3.11 with awkward v2.x
         if: matrix.python-version == 3.11
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 1d056200..11d49f51 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -19,7 +19,7 @@ repos:
       - id: trailing-whitespace
 
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: "v0.5.7"
+    rev: "v0.6.1"
     hooks:
       - id: ruff
         args: ["--fix", "--show-fixes"]
diff --git a/docs/usage/intro.ipynb b/docs/usage/intro.ipynb
index 54164e0e..f86022cf 100644
--- a/docs/usage/intro.ipynb
+++ b/docs/usage/intro.ipynb
@@ -34,6 +34,8 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "from __future__ import annotations\n",
+    "\n",
     "import numbers\n",
     "\n",
     "import awkward as ak  # at least version 1.2.0rc5\n",
@@ -3249,12 +3251,12 @@
     "v1 = vector.obj(x=1, y=2, z=3)\n",
     "v2 = vector.obj(x=1, y=2)\n",
     "\n",
-    "print(v1 - v2.like(v1))           # transforms v2 to v1's coordinate system (imputes z=0)\n",
-    "print(v1.like(v2) - v2)           # transforms v1 to v2's coordinate system (removes z)\n",
-    "print(v1 - v2.to_xyz())           # transforms v2 to xyz coordinates (imputes z=0)\n",
-    "print(v1.to_xy() - v2)            # transforms v1 to xy coordinates (removes z)\n",
-    "print(v1 - v2.to_Vector3D(z=3))   # transforms v2 to 3D (imputes z=3)\n",
-    "print(v1.to_Vector2D() - v2)      # transforms v1 to 2D (removes z)"
+    "print(v1 - v2.like(v1))  # transforms v2 to v1's coordinate system (imputes z=0)\n",
+    "print(v1.like(v2) - v2)  # transforms v1 to v2's coordinate system (removes z)\n",
+    "print(v1 - v2.to_xyz())  # transforms v2 to xyz coordinates (imputes z=0)\n",
+    "print(v1.to_xy() - v2)  # transforms v1 to xy coordinates (removes z)\n",
+    "print(v1 - v2.to_Vector3D(z=3))  # transforms v2 to 3D (imputes z=3)\n",
+    "print(v1.to_Vector2D() - v2)  # transforms v1 to 2D (removes z)"
    ]
   },
   {
@@ -3573,10 +3575,12 @@
     "class TwoVector(vector.backends.awkward.MomentumAwkward2D):\n",
     "    pass\n",
     "\n",
+    "\n",
     "@ak.mixin_class(behavior)\n",
     "class ThreeVector(vector.backends.awkward.MomentumAwkward3D):\n",
     "    pass\n",
     "\n",
+    "\n",
     "# required for transforming vectors\n",
     "# the class names must always end with \"Array\"\n",
     "TwoVectorArray.ProjectionClass2D = TwoVectorArray  # noqa: F821\n",
@@ -3857,10 +3861,10 @@
    "outputs": [],
    "source": [
     "_binary_dispatch_cls = {\n",
-    "     \"TwoVector\": TwoVector,\n",
-    "     \"ThreeVector\": ThreeVector,\n",
-    "     \"LorentzVector\": LorentzVector,\n",
-    " }\n",
+    "    \"TwoVector\": TwoVector,\n",
+    "    \"ThreeVector\": ThreeVector,\n",
+    "    \"LorentzVector\": LorentzVector,\n",
+    "}\n",
     "_rank = [TwoVector, ThreeVector, LorentzVector]\n",
     "\n",
     "for lhs, lhs_to in _binary_dispatch_cls.items():\n",
@@ -3951,21 +3955,9 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "behavior.update(\n",
-    "    ak._util.copy_behaviors(\n",
-    "        \"Vector2D\", \"TwoVector\", behavior\n",
-    "    )\n",
-    ")\n",
-    "behavior.update(\n",
-    "    ak._util.copy_behaviors(\n",
-    "        \"Vector3D\", \"ThreeVector\", behavior\n",
-    "    )\n",
-    ")\n",
-    "behavior.update(\n",
-    "    ak._util.copy_behaviors(\n",
-    "        \"Momentum4D\", \"LorentzVector\", behavior\n",
-    "    )\n",
-    ")"
+    "behavior.update(ak._util.copy_behaviors(\"Vector2D\", \"TwoVector\", behavior))\n",
+    "behavior.update(ak._util.copy_behaviors(\"Vector3D\", \"ThreeVector\", behavior))\n",
+    "behavior.update(ak._util.copy_behaviors(\"Momentum4D\", \"LorentzVector\", behavior))"
    ]
   },
   {
diff --git a/pyproject.toml b/pyproject.toml
index 474d6fbd..3c12495b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -42,7 +42,7 @@ dynamic = [
   "version",
 ]
 dependencies = [
-  "numpy>=1.13.3",
+  "numpy>=1.13.3,<2.1",
   "packaging>=19",
 ]
 optional-dependencies.awkward = [
@@ -137,6 +137,9 @@ isort.required-imports = [
 "tests/*" = [
   "T20",
 ]
+"docs/usage/intro.ipynb" = [
+  "T20",
+]
 "src/vector/backends/_numba_object.py" = [
   "PGH003",
 ]
diff --git a/tests/test_compute_features.py b/tests/test_compute_features.py
index e5185771..844167e3 100644
--- a/tests/test_compute_features.py
+++ b/tests/test_compute_features.py
@@ -99,7 +99,7 @@
 
 
 @pytest.mark.skipif(is_unsupported, reason=unsupported_message)
-@pytest.mark.slow()
+@pytest.mark.slow
 @pytest.mark.parametrize("signature", functions.keys())
 def test(signature):
     analyze_function(functions[signature])
diff --git a/tests/test_notebooks.py b/tests/test_notebooks.py
index bdaed1cc..f06a4d42 100644
--- a/tests/test_notebooks.py
+++ b/tests/test_notebooks.py
@@ -7,7 +7,7 @@
 import pytest
 
 
-@pytest.fixture()
+@pytest.fixture
 def common_kwargs(tmpdir):
     outputnb = tmpdir.join("output.ipynb")
     return {