diff --git a/.github/actions/create-dev-env/action.yml b/.github/actions/create-dev-env/action.yml
index c7b008b8..1a0e6221 100644
--- a/.github/actions/create-dev-env/action.yml
+++ b/.github/actions/create-dev-env/action.yml
@@ -7,7 +7,7 @@ runs:
     - name: Set Up Python 🐍
       uses: actions/setup-python@v5
       with:
-        python-version: "3.12"
+        python-version: 3.12
 
     - name: Install Dev Dependencies 📦
       run: |
diff --git a/.github/workflows/pre-commit.yml b/.github/workflows/pre-commit.yml
index 42c9b837..76f38132 100644
--- a/.github/workflows/pre-commit.yml
+++ b/.github/workflows/pre-commit.yml
@@ -21,7 +21,7 @@ jobs:
       - name: Set Up Python 🐍
         uses: actions/setup-python@v5
         with:
-          python-version: 3.x
+          python-version: 3.12
 
       - name: Install pre-commit 📦
         run: |
diff --git a/.github/workflows/sphinx.yml b/.github/workflows/sphinx.yml
index e6211d16..63f44369 100644
--- a/.github/workflows/sphinx.yml
+++ b/.github/workflows/sphinx.yml
@@ -38,7 +38,7 @@ jobs:
       - name: Set Up Python 🐍
         uses: actions/setup-python@v5
         with:
-          python-version: 3.9
+          python-version: 3.12
 
       - name: Install Doc Dependencies 📦
         run: |
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 57802ee1..43c3d17f 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -17,7 +17,7 @@ repos:
     rev: v3.19.1
     hooks:
       - id: pyupgrade
-        args: [--py39-plus]
+        args: [--py312-plus]
 
   # Automatically sort python imports
   - repo: https://github.com/PyCQA/isort
@@ -31,7 +31,7 @@ repos:
     rev: 25.1.0
     hooks:
       - id: black
-        args: [--target-version=py39]
+        args: [--target-version=py312]
 
   # Check python code static typing
   - repo: https://github.com/pre-commit/mirrors-mypy
@@ -141,10 +141,10 @@ repos:
     rev: 1.9.1
     hooks:
       - id: nbqa-pyupgrade
-        args: [--py39-plus]
+        args: [--py312-plus]
       - id: nbqa-isort
       - id: nbqa-black
-        args: [--target-version=py39]
+        args: [--target-version=py312]
       - id: nbqa-flake8
 
   # Run black on python code blocks in documentation files.
@@ -156,7 +156,7 @@ repos:
         # the python code blocks include jupyter-specific additions such as % or !
         # See https://github.com/adamchainz/blacken-docs/issues/127 for an upstream
         # feature request about this.
-        args: [--target-version=py39, --skip-errors]
+        args: [--target-version=py312, --skip-errors]
 
 # pre-commit.ci config reference: https://pre-commit.ci/#configuration
 ci:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 80082eeb..8a1d239e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ Affected: all images.
 - **Non-breaking:** don't create extra free space in runners for cuda images ([#2218](https://github.com/jupyter/docker-stacks/pull/2218)).
 - **Non-breaking:** revert "Pin some packages to fix `r-notebook` and `datascience-notebook` under aarch64" ([#2220](https://github.com/jupyter/docker-stacks/pull/2220)).
 - **Non-breaking:** Simplify and improve `test_packages.py` ([#2219](https://github.com/jupyter/docker-stacks/pull/2219)).
+- **Non-breaking:** Use Python 3.12 for internal code ([#2222](https://github.com/jupyter/docker-stacks/pull/2222)).
 
 ## 2025-02-17
 
diff --git a/mypy.ini b/mypy.ini
index 3e20bf5b..c2ea66fa 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -8,7 +8,7 @@
 # We use mypy as part of pre-commit checks
 
 [mypy]
-python_version = 3.9
+python_version = 3.12
 follow_imports = error
 strict = True
 no_incremental = True
diff --git a/tagging/docker_runner.py b/tagging/docker_runner.py
index 9d71f27b..c2020109 100644
--- a/tagging/docker_runner.py
+++ b/tagging/docker_runner.py
@@ -2,7 +2,6 @@
 # Distributed under the terms of the Modified BSD License.
 import logging
 from types import TracebackType
-from typing import Optional
 
 import docker
 from docker.models.containers import Container
@@ -17,7 +16,7 @@ class DockerRunner:
         docker_client: docker.DockerClient = docker.from_env(),
         command: str = "sleep infinity",
     ):
-        self.container: Optional[Container] = None
+        self.container: Container | None = None
         self.image_name: str = image_name
         self.command: str = command
         self.docker_client: docker.DockerClient = docker_client
@@ -34,9 +33,9 @@ class DockerRunner:
 
     def __exit__(
         self,
-        exc_type: Optional[type[BaseException]],
-        exc_val: Optional[BaseException],
-        exc_tb: Optional[TracebackType],
+        exc_type: type[BaseException] | None,
+        exc_val: BaseException | None,
+        exc_tb: TracebackType | None,
     ) -> None:
         assert self.container is not None
         LOGGER.info(f"Removing container {self.container.name} ...")
diff --git a/tagging/get_taggers_and_manifests.py b/tagging/get_taggers_and_manifests.py
index d41d7a86..3c39b532 100644
--- a/tagging/get_taggers_and_manifests.py
+++ b/tagging/get_taggers_and_manifests.py
@@ -1,6 +1,5 @@
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
-from typing import Optional
 
 from tagging.images_hierarchy import ALL_IMAGES
 from tagging.manifests import ManifestInterface
@@ -8,7 +7,7 @@ from tagging.taggers import TaggerInterface
 
 
 def get_taggers_and_manifests(
-    short_image_name: Optional[str],
+    short_image_name: str | None,
 ) -> tuple[list[TaggerInterface], list[ManifestInterface]]:
     if short_image_name is None:
         return [[], []]  # type: ignore
diff --git a/tagging/images_hierarchy.py b/tagging/images_hierarchy.py
index 8c3e3fd3..3a15faa0 100644
--- a/tagging/images_hierarchy.py
+++ b/tagging/images_hierarchy.py
@@ -1,7 +1,6 @@
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
 from dataclasses import dataclass, field
-from typing import Optional
 
 from tagging.manifests import (
     AptPackagesManifest,
@@ -32,7 +31,7 @@ from tagging.taggers import (
 
 @dataclass
 class ImageDescription:
-    parent_image: Optional[str]
+    parent_image: str | None
     taggers: list[TaggerInterface] = field(default_factory=list)
     manifests: list[ManifestInterface] = field(default_factory=list)
 
diff --git a/tests/base-notebook/test_healthcheck.py b/tests/base-notebook/test_healthcheck.py
index 36a8a4dc..c3684b18 100644
--- a/tests/base-notebook/test_healthcheck.py
+++ b/tests/base-notebook/test_healthcheck.py
@@ -2,7 +2,6 @@
 # Distributed under the terms of the Modified BSD License.
 import logging
 import time
-from typing import Optional
 
 import pytest  # type: ignore
 
@@ -56,9 +55,9 @@ LOGGER = logging.getLogger(__name__)
 )
 def test_healthy(
     container: TrackedContainer,
-    env: Optional[list[str]],
-    cmd: Optional[list[str]],
-    user: Optional[str],
+    env: list[str] | None,
+    cmd: list[str] | None,
+    user: str | None,
 ) -> None:
     running_container = container.run_detached(
         tty=True,
@@ -104,9 +103,9 @@ def test_healthy(
 )
 def test_healthy_with_proxy(
     container: TrackedContainer,
-    env: Optional[list[str]],
-    cmd: Optional[list[str]],
-    user: Optional[str],
+    env: list[str] | None,
+    cmd: list[str] | None,
+    user: str | None,
 ) -> None:
     running_container = container.run_detached(
         tty=True,
@@ -142,8 +141,8 @@ def test_healthy_with_proxy(
 )
 def test_not_healthy(
     container: TrackedContainer,
-    env: Optional[list[str]],
-    cmd: Optional[list[str]],
+    env: list[str] | None,
+    cmd: list[str] | None,
 ) -> None:
     running_container = container.run_detached(
         tty=True,
diff --git a/tests/base-notebook/test_start_container.py b/tests/base-notebook/test_start_container.py
index 729e7cac..e938f78a 100644
--- a/tests/base-notebook/test_start_container.py
+++ b/tests/base-notebook/test_start_container.py
@@ -2,7 +2,6 @@
 # Distributed under the terms of the Modified BSD License.
 import logging
 import time
-from typing import Optional
 
 import pytest  # type: ignore
 import requests
@@ -32,7 +31,7 @@ LOGGER = logging.getLogger(__name__)
 def test_start_notebook(
     container: TrackedContainer,
     http_client: requests.Session,
-    env: Optional[list[str]],
+    env: list[str] | None,
     expected_command: str,
     expected_start: bool,
     expected_warnings: list[str],
diff --git a/tests/conftest.py b/tests/conftest.py
index 1df04b60..6df248a5 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -4,7 +4,7 @@ import logging
 import os
 import socket
 from contextlib import closing
-from typing import Any, Optional
+from typing import Any
 
 import docker
 import pytest  # type: ignore
@@ -72,7 +72,7 @@ class TrackedContainer:
         image_name: str,
         **kwargs: Any,
     ):
-        self.container: Optional[Container] = None
+        self.container: Container | None = None
         self.docker_client: docker.DockerClient = docker_client
         self.image_name: str = image_name
         self.kwargs: Any = kwargs
diff --git a/tests/docker-stacks-foundation/test_packages.py b/tests/docker-stacks-foundation/test_packages.py
index f68d6ec9..d2d2f193 100644
--- a/tests/docker-stacks-foundation/test_packages.py
+++ b/tests/docker-stacks-foundation/test_packages.py
@@ -40,8 +40,7 @@ Example:
 """
 
 import logging
-from collections.abc import Iterable
-from typing import Callable
+from collections.abc import Callable, Iterable
 
 import pytest  # type: ignore
 
diff --git a/tests/images_hierarchy.py b/tests/images_hierarchy.py
index 193ec270..df583bd9 100644
--- a/tests/images_hierarchy.py
+++ b/tests/images_hierarchy.py
@@ -1,7 +1,6 @@
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
 from pathlib import Path
-from typing import Optional
 
 THIS_DIR = Path(__file__).parent.resolve()
 
@@ -23,7 +22,7 @@ ALL_IMAGES = {
 
 
 def get_test_dirs(
-    short_image_name: Optional[str],
+    short_image_name: str | None,
 ) -> list[Path]:
     if short_image_name is None:
         return []
diff --git a/tests/package_helper.py b/tests/package_helper.py
index 6c5930b7..b5e0e415 100644
--- a/tests/package_helper.py
+++ b/tests/package_helper.py
@@ -27,7 +27,7 @@ import logging
 import re
 from collections import defaultdict
 from itertools import chain
-from typing import Any, Optional
+from typing import Any
 
 from docker.models.containers import Container
 from tabulate import tabulate
@@ -44,9 +44,9 @@ class CondaPackageHelper:
         self.running_container: Container = CondaPackageHelper.start_container(
             container
         )
-        self.requested: Optional[dict[str, set[str]]] = None
-        self.installed: Optional[dict[str, set[str]]] = None
-        self.available: Optional[dict[str, set[str]]] = None
+        self.requested: dict[str, set[str]] | None = None
+        self.installed: dict[str, set[str]] | None = None
+        self.available: dict[str, set[str]] | None = None
         self.comparison: list[dict[str, str]] = []
 
     @staticmethod