diff --git a/noxfile.py b/noxfile.py
index 5c20487ccd..48f345bbc7 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -77,9 +77,7 @@
 UNIT_TEST_LOCAL_DEPENDENCIES: List[str] = []
 UNIT_TEST_DEPENDENCIES: List[str] = []
 UNIT_TEST_EXTRAS: List[str] = ["tests"]
-UNIT_TEST_EXTRAS_BY_PYTHON: Dict[str, List[str]] = {
-    "3.12": ["polars", "scikit-learn"],
-}
+UNIT_TEST_EXTRAS_BY_PYTHON: Dict[str, List[str]] = {}
 
 # 3.10 is needed for Windows tests as it is the only version installed in the
 # bigframes-windows container image. For more information, search
@@ -103,13 +101,8 @@
 ]
 SYSTEM_TEST_LOCAL_DEPENDENCIES: List[str] = []
 SYSTEM_TEST_DEPENDENCIES: List[str] = []
-SYSTEM_TEST_EXTRAS: List[str] = []
-SYSTEM_TEST_EXTRAS_BY_PYTHON: Dict[str, List[str]] = {
-    "3.9": ["tests"],
-    "3.10": ["tests"],
-    "3.12": ["tests", "scikit-learn"],
-    "3.13": ["tests"],
-}
+SYSTEM_TEST_EXTRAS: List[str] = ["tests"]
+SYSTEM_TEST_EXTRAS_BY_PYTHON: Dict[str, List[str]] = {}
 
 LOGGING_NAME_ENV_VAR = "BIGFRAMES_PERFORMANCE_LOG_NAME"
 
@@ -312,7 +305,7 @@ def install_systemtest_dependencies(session, install_test_extra, *constraints):
 
     if install_test_extra and SYSTEM_TEST_EXTRAS_BY_PYTHON:
         extras = SYSTEM_TEST_EXTRAS_BY_PYTHON.get(session.python, [])
-    elif install_test_extra and SYSTEM_TEST_EXTRAS:
+    if install_test_extra and SYSTEM_TEST_EXTRAS:
         extras = SYSTEM_TEST_EXTRAS
     else:
         extras = []
@@ -489,7 +482,7 @@ def cover(session):
 @nox.session(python=DEFAULT_PYTHON_VERSION)
 def docs(session):
     """Build the docs for this library."""
-    session.install("-e", ".[scikit-learn]")
+    session.install("-e", ".[tests]")
     session.install(
         # We need to pin to specific versions of the `sphinxcontrib-*` packages
         # which still support sphinx 4.x.
@@ -530,7 +523,7 @@ def docs(session):
 def docfx(session):
     """Build the docfx yaml files for this library."""
 
-    session.install("-e", ".[scikit-learn]")
+    session.install("-e", ".[tests]")
     session.install(
         # We need to pin to specific versions of the `sphinxcontrib-*` packages
         # which still support sphinx 4.x.
diff --git a/setup.py b/setup.py
index edd8e63e65..706cfefa09 100644
--- a/setup.py
+++ b/setup.py
@@ -72,13 +72,12 @@
     # Optional test dependencies packages. If they're missed, may skip some tests.
     "tests": [
         "freezegun",
-        "pytest-snapshot",
         "google-cloud-bigtable >=2.24.0",
         "google-cloud-pubsub >=2.21.4",
+        "polars >= 1.7.0",
+        "pytest-snapshot",
+        "scikit-learn>=1.2.2",
     ],
-    # used for local engine, which is only needed for unit tests at present.
-    "polars": ["polars >= 1.7.0"],
-    "scikit-learn": ["scikit-learn>=1.2.2"],
     # Packages required for basic development flow.
     "dev": [
         "pytest",