diff --git a/.github/workflows/python-tests.yml b/.github/workflows/python-tests.yml
index 83c949e6ca..709a190ac6 100644
--- a/.github/workflows/python-tests.yml
+++ b/.github/workflows/python-tests.yml
@@ -18,12 +18,12 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: ["3.8", "3.11"]
+        python-version: ["3.9", "3.11", "3.12"]
         include:
           - os: windows-latest
             python-version: "3.9"
           - os: ubuntu-latest
-            python-version: "pypy-3.8"
+            python-version: "pypy-3.9"
           - os: macos-latest
             python-version: "3.10"
           - os: ubuntu-latest
@@ -180,7 +180,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        python-version: ["3.8", "3.9", "3.10", "3.11"]
+        python-version: ["3.9", "3.10", "3.11", "3.12"]
     steps:
       - uses: actions/checkout@v4
       - uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
@@ -194,7 +194,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
         with:
-          python_version: "pypy-3.8"
+          python_version: "pypy-3.9"
       - name: Run the tests
         run: hatch -v run test:nowarn --integration_tests=true
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index cadf2e8a93..73e03df6d0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,104 @@ All notable changes to this project will be documented in this file.
 
 <!-- <START NEW CHANGELOG ENTRY> -->
 
+## 2.15.0
+
+([Full Changelog](https://github.com/jupyter-server/jupyter_server/compare/v2.9.1...f23b3392624001c8fba6623e19f526a98b4a07ba))
+
+### Enhancements made
+
+- Better error message when starting kernel for session. [#1478](https://github.com/jupyter-server/jupyter_server/pull/1478) ([@Carreau](https://github.com/Carreau))
+- Add a traitlet to disable recording HTTP request metrics [#1472](https://github.com/jupyter-server/jupyter_server/pull/1472) ([@yuvipanda](https://github.com/yuvipanda))
+- prometheus: Expose 3 activity metrics [#1471](https://github.com/jupyter-server/jupyter_server/pull/1471) ([@yuvipanda](https://github.com/yuvipanda))
+- Add prometheus info metrics listing server extensions + versions [#1470](https://github.com/jupyter-server/jupyter_server/pull/1470) ([@yuvipanda](https://github.com/yuvipanda))
+- Add prometheus metric with version information [#1467](https://github.com/jupyter-server/jupyter_server/pull/1467) ([@yuvipanda](https://github.com/yuvipanda))
+- Better hash format error message [#1442](https://github.com/jupyter-server/jupyter_server/pull/1442) ([@fcollonval](https://github.com/fcollonval))
+- Removing excessive logging from reading local files [#1420](https://github.com/jupyter-server/jupyter_server/pull/1420) ([@lresende](https://github.com/lresende))
+- Do not include token in dashboard link, when available [#1406](https://github.com/jupyter-server/jupyter_server/pull/1406) ([@minrk](https://github.com/minrk))
+- Add an option to have authentication enabled for all endpoints by default [#1392](https://github.com/jupyter-server/jupyter_server/pull/1392) ([@krassowski](https://github.com/krassowski))
+- websockets: add configurations for ping interval and timeout [#1391](https://github.com/jupyter-server/jupyter_server/pull/1391) ([@oliver-sanders](https://github.com/oliver-sanders))
+- log extension import time at debug level unless it's actually slow [#1375](https://github.com/jupyter-server/jupyter_server/pull/1375) ([@minrk](https://github.com/minrk))
+- Add support for async Authorizers (part 2) [#1374](https://github.com/jupyter-server/jupyter_server/pull/1374) ([@Zsailer](https://github.com/Zsailer))
+- Support async Authorizers [#1373](https://github.com/jupyter-server/jupyter_server/pull/1373) ([@Zsailer](https://github.com/Zsailer))
+- Support get file(notebook) md5 [#1363](https://github.com/jupyter-server/jupyter_server/pull/1363) ([@Wh1isper](https://github.com/Wh1isper))
+- Update kernel env to reflect changes in session [#1354](https://github.com/jupyter-server/jupyter_server/pull/1354) ([@blink1073](https://github.com/blink1073))
+
+### Bugs fixed
+
+- Return HTTP 400 when attempting to post an event with an unregistered schema [#1463](https://github.com/jupyter-server/jupyter_server/pull/1463) ([@afshin](https://github.com/afshin))
+- write server extension list to stdout [#1451](https://github.com/jupyter-server/jupyter_server/pull/1451) ([@minrk](https://github.com/minrk))
+- don't let ExtensionApp jpserver_extensions be overridden by config [#1447](https://github.com/jupyter-server/jupyter_server/pull/1447) ([@minrk](https://github.com/minrk))
+- Pass session_id during Websocket connect [#1440](https://github.com/jupyter-server/jupyter_server/pull/1440) ([@gogasca](https://github.com/gogasca))
+- Do not log environment variables passed to kernels [#1437](https://github.com/jupyter-server/jupyter_server/pull/1437) ([@krassowski](https://github.com/krassowski))
+- extensions: render default templates with default static_url [#1435](https://github.com/jupyter-server/jupyter_server/pull/1435) ([@minrk](https://github.com/minrk))
+- Improve the busy/idle execution state tracking for kernels. [#1429](https://github.com/jupyter-server/jupyter_server/pull/1429) ([@ojarjur](https://github.com/ojarjur))
+- Ignore zero-length page_config.json, restore previous behavior of crashing for invalid JSON [#1405](https://github.com/jupyter-server/jupyter_server/pull/1405) ([@holzman](https://github.com/holzman))
+- Don't crash on invalid JSON in page_config (#1403) [#1404](https://github.com/jupyter-server/jupyter_server/pull/1404) ([@holzman](https://github.com/holzman))
+- Fix color in windows log console with colorama [#1397](https://github.com/jupyter-server/jupyter_server/pull/1397) ([@hansepac](https://github.com/hansepac))
+- Fix log arguments for gateway client error [#1385](https://github.com/jupyter-server/jupyter_server/pull/1385) ([@minrk](https://github.com/minrk))
+- Import User unconditionally [#1384](https://github.com/jupyter-server/jupyter_server/pull/1384) ([@yuvipanda](https://github.com/yuvipanda))
+- Fix a typo in error message [#1381](https://github.com/jupyter-server/jupyter_server/pull/1381) ([@krassowski](https://github.com/krassowski))
+- avoid unhandled error on some invalid paths [#1369](https://github.com/jupyter-server/jupyter_server/pull/1369) ([@minrk](https://github.com/minrk))
+- Change md5 to hash and hash_algorithm, fix incompatibility [#1367](https://github.com/jupyter-server/jupyter_server/pull/1367) ([@Wh1isper](https://github.com/Wh1isper))
+- ContentsHandler return 404 rather than raise exc [#1357](https://github.com/jupyter-server/jupyter_server/pull/1357) ([@bloomsa](https://github.com/bloomsa))
+- Force legacy ws subprotocol when using gateway [#1311](https://github.com/jupyter-server/jupyter_server/pull/1311) ([@epignot](https://github.com/epignot))
+
+### Maintenance and upkeep improvements
+
+- Donation link NF -> LF [#1485](https://github.com/jupyter-server/jupyter_server/pull/1485) ([@Carreau](https://github.com/Carreau))
+- Handle newer jupyter_events wants string version, drop 3.8 [#1481](https://github.com/jupyter-server/jupyter_server/pull/1481) ([@Carreau](https://github.com/Carreau))
+- Ignore unclosed sqlite connection in traits [#1477](https://github.com/jupyter-server/jupyter_server/pull/1477) ([@cjwatson](https://github.com/cjwatson))
+- chore: update pre-commit hooks [#1441](https://github.com/jupyter-server/jupyter_server/pull/1441) ([@pre-commit-ci](https://github.com/pre-commit-ci))
+- chore: update pre-commit hooks [#1427](https://github.com/jupyter-server/jupyter_server/pull/1427) ([@pre-commit-ci](https://github.com/pre-commit-ci))
+- Use hatch fmt command [#1424](https://github.com/jupyter-server/jupyter_server/pull/1424) ([@blink1073](https://github.com/blink1073))
+- chore: update pre-commit hooks [#1421](https://github.com/jupyter-server/jupyter_server/pull/1421) ([@pre-commit-ci](https://github.com/pre-commit-ci))
+- Fix jupytext and lint CI failures [#1413](https://github.com/jupyter-server/jupyter_server/pull/1413) ([@blink1073](https://github.com/blink1073))
+- Set all min deps [#1411](https://github.com/jupyter-server/jupyter_server/pull/1411) ([@blink1073](https://github.com/blink1073))
+- chore: update pre-commit hooks [#1409](https://github.com/jupyter-server/jupyter_server/pull/1409) ([@pre-commit-ci](https://github.com/pre-commit-ci))
+- Update pytest requirement from \<8,>=7.0 to >=7.0,\<9 [#1402](https://github.com/jupyter-server/jupyter_server/pull/1402) ([@dependabot](https://github.com/dependabot))
+- Pin to Pytest 7 [#1401](https://github.com/jupyter-server/jupyter_server/pull/1401) ([@blink1073](https://github.com/blink1073))
+- Update release workflows [#1399](https://github.com/jupyter-server/jupyter_server/pull/1399) ([@blink1073](https://github.com/blink1073))
+- chore: update pre-commit hooks [#1390](https://github.com/jupyter-server/jupyter_server/pull/1390) ([@pre-commit-ci](https://github.com/pre-commit-ci))
+- Improve warning handling [#1386](https://github.com/jupyter-server/jupyter_server/pull/1386) ([@blink1073](https://github.com/blink1073))
+- Simplify the jupytext downstream test [#1383](https://github.com/jupyter-server/jupyter_server/pull/1383) ([@mwouts](https://github.com/mwouts))
+- Fix test param for pytest-xdist [#1382](https://github.com/jupyter-server/jupyter_server/pull/1382) ([@tornaria](https://github.com/tornaria))
+- Update pre-commit deps [#1380](https://github.com/jupyter-server/jupyter_server/pull/1380) ([@blink1073](https://github.com/blink1073))
+- Use ruff docstring-code-format [#1377](https://github.com/jupyter-server/jupyter_server/pull/1377) ([@blink1073](https://github.com/blink1073))
+- Update for tornado 6.4 [#1372](https://github.com/jupyter-server/jupyter_server/pull/1372) ([@blink1073](https://github.com/blink1073))
+- chore: update pre-commit hooks [#1370](https://github.com/jupyter-server/jupyter_server/pull/1370) ([@pre-commit-ci](https://github.com/pre-commit-ci))
+- Update ruff and typings [#1365](https://github.com/jupyter-server/jupyter_server/pull/1365) ([@blink1073](https://github.com/blink1073))
+- Clean up ruff config [#1358](https://github.com/jupyter-server/jupyter_server/pull/1358) ([@blink1073](https://github.com/blink1073))
+- Add more typings [#1356](https://github.com/jupyter-server/jupyter_server/pull/1356) ([@blink1073](https://github.com/blink1073))
+- chore: update pre-commit hooks [#1355](https://github.com/jupyter-server/jupyter_server/pull/1355) ([@pre-commit-ci](https://github.com/pre-commit-ci))
+- Clean up config and address warnings [#1353](https://github.com/jupyter-server/jupyter_server/pull/1353) ([@blink1073](https://github.com/blink1073))
+- Clean up lint and typing [#1351](https://github.com/jupyter-server/jupyter_server/pull/1351) ([@blink1073](https://github.com/blink1073))
+- Update typing for traitlets 5.13 [#1350](https://github.com/jupyter-server/jupyter_server/pull/1350) ([@blink1073](https://github.com/blink1073))
+- Update typings and fix tests [#1344](https://github.com/jupyter-server/jupyter_server/pull/1344) ([@blink1073](https://github.com/blink1073))
+
+### Documentation improvements
+
+- add comments to explain signal handling under jupyterhub [#1452](https://github.com/jupyter-server/jupyter_server/pull/1452) ([@oliver-sanders](https://github.com/oliver-sanders))
+- Update documentation for `cookie_secret` [#1433](https://github.com/jupyter-server/jupyter_server/pull/1433) ([@krassowski](https://github.com/krassowski))
+- Add Changelog for 2.14.1 [#1430](https://github.com/jupyter-server/jupyter_server/pull/1430) ([@blink1073](https://github.com/blink1073))
+- Update simple extension examples: \_jupyter_server_extension_points [#1426](https://github.com/jupyter-server/jupyter_server/pull/1426) ([@manics](https://github.com/manics))
+- Link to GitHub repo from the docs [#1415](https://github.com/jupyter-server/jupyter_server/pull/1415) ([@krassowski](https://github.com/krassowski))
+- docs: list server extensions [#1412](https://github.com/jupyter-server/jupyter_server/pull/1412) ([@oliver-sanders](https://github.com/oliver-sanders))
+- Update simple extension README to cd into correct subdirectory [#1410](https://github.com/jupyter-server/jupyter_server/pull/1410) ([@markypizz](https://github.com/markypizz))
+- Add deprecation note for `ServerApp.preferred_dir` [#1396](https://github.com/jupyter-server/jupyter_server/pull/1396) ([@krassowski](https://github.com/krassowski))
+- Replace \_jupyter_server_extension_paths in apidocs [#1393](https://github.com/jupyter-server/jupyter_server/pull/1393) ([@manics](https://github.com/manics))
+- fix "Shutdown" -> "Shut down" [#1389](https://github.com/jupyter-server/jupyter_server/pull/1389) ([@Timeroot](https://github.com/Timeroot))
+- Enable htmlzip and epub on readthedocs [#1379](https://github.com/jupyter-server/jupyter_server/pull/1379) ([@bollwyvl](https://github.com/bollwyvl))
+- Update api docs with md5 param [#1364](https://github.com/jupyter-server/jupyter_server/pull/1364) ([@Wh1isper](https://github.com/Wh1isper))
+- typo: ServerApp [#1361](https://github.com/jupyter-server/jupyter_server/pull/1361) ([@IITII](https://github.com/IITII))
+
+### Contributors to this release
+
+([GitHub contributors page for this release](https://github.com/jupyter-server/jupyter_server/graphs/contributors?from=2023-10-25&to=2024-12-20&type=c))
+
+[@afshin](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Aafshin+updated%3A2023-10-25..2024-12-20&type=Issues) | [@blink1073](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Ablink1073+updated%3A2023-10-25..2024-12-20&type=Issues) | [@bloomsa](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Abloomsa+updated%3A2023-10-25..2024-12-20&type=Issues) | [@bollwyvl](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Abollwyvl+updated%3A2023-10-25..2024-12-20&type=Issues) | [@Carreau](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3ACarreau+updated%3A2023-10-25..2024-12-20&type=Issues) | [@cjwatson](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Acjwatson+updated%3A2023-10-25..2024-12-20&type=Issues) | [@davidbrochart](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Adavidbrochart+updated%3A2023-10-25..2024-12-20&type=Issues) | [@dependabot](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Adependabot+updated%3A2023-10-25..2024-12-20&type=Issues) | [@epignot](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Aepignot+updated%3A2023-10-25..2024-12-20&type=Issues) | [@fcollonval](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Afcollonval+updated%3A2023-10-25..2024-12-20&type=Issues) | [@gogasca](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Agogasca+updated%3A2023-10-25..2024-12-20&type=Issues) | [@hansepac](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Ahansepac+updated%3A2023-10-25..2024-12-20&type=Issues) | [@holzman](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Aholzman+updated%3A2023-10-25..2024-12-20&type=Issues) | [@IITII](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3AIITII+updated%3A2023-10-25..2024-12-20&type=Issues) | [@krassowski](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Akrassowski+updated%3A2023-10-25..2024-12-20&type=Issues) | [@lresende](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Alresende+updated%3A2023-10-25..2024-12-20&type=Issues) | [@manics](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Amanics+updated%3A2023-10-25..2024-12-20&type=Issues) | [@markypizz](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Amarkypizz+updated%3A2023-10-25..2024-12-20&type=Issues) | [@minrk](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Aminrk+updated%3A2023-10-25..2024-12-20&type=Issues) | [@mwouts](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Amwouts+updated%3A2023-10-25..2024-12-20&type=Issues) | [@ojarjur](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Aojarjur+updated%3A2023-10-25..2024-12-20&type=Issues) | [@oliver-sanders](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Aoliver-sanders+updated%3A2023-10-25..2024-12-20&type=Issues) | [@pre-commit-ci](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Apre-commit-ci+updated%3A2023-10-25..2024-12-20&type=Issues) | [@Timeroot](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3ATimeroot+updated%3A2023-10-25..2024-12-20&type=Issues) | [@tornaria](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Atornaria+updated%3A2023-10-25..2024-12-20&type=Issues) | [@welcome](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Awelcome+updated%3A2023-10-25..2024-12-20&type=Issues) | [@Wh1isper](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3AWh1isper+updated%3A2023-10-25..2024-12-20&type=Issues) | [@yuvipanda](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Ayuvipanda+updated%3A2023-10-25..2024-12-20&type=Issues) | [@Zsailer](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3AZsailer+updated%3A2023-10-25..2024-12-20&type=Issues)
+
+<!-- <END NEW CHANGELOG ENTRY> -->
+
 ## 2.14.2
 
 ([Full Changelog](https://github.com/jupyter-server/jupyter_server/compare/v2.14.1...b961d4eb499071c0c60e24f429c20d1e6a908a32))
@@ -30,8 +128,6 @@ All notable changes to this project will be documented in this file.
 
 [@blink1073](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Ablink1073+updated%3A2024-05-31..2024-07-12&type=Issues) | [@gogasca](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Agogasca+updated%3A2024-05-31..2024-07-12&type=Issues) | [@krassowski](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Akrassowski+updated%3A2024-05-31..2024-07-12&type=Issues) | [@manics](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Amanics+updated%3A2024-05-31..2024-07-12&type=Issues) | [@pre-commit-ci](https://github.com/search?q=repo%3Ajupyter-server%2Fjupyter_server+involves%3Apre-commit-ci+updated%3A2024-05-31..2024-07-12&type=Issues)
 
-<!-- <END NEW CHANGELOG ENTRY> -->
-
 ## 2.14.1
 
 ([Full Changelog](https://github.com/jupyter-server/jupyter_server/compare/v2.14.0...f1379164fa209bc4bfeadf43ab0e7f473b03a0ce))
diff --git a/examples/simple/pyproject.toml b/examples/simple/pyproject.toml
index 38ae8e71a7..9dec3e55c7 100644
--- a/examples/simple/pyproject.toml
+++ b/examples/simple/pyproject.toml
@@ -6,8 +6,8 @@ build-backend = "hatchling.build"
 name = "jupyter-server-example"
 description = "Jupyter Server Example"
 readme = "README.md"
-license = ""
-requires-python = ">=3.8"
+license = "MIT"
+requires-python = ">=3.9"
 dependencies = [
     "jinja2",
     "jupyter_server",
diff --git a/examples/simple/simple_ext1/handlers.py b/examples/simple/simple_ext1/handlers.py
index 72f54a8bfd..6ac99f64a4 100644
--- a/examples/simple/simple_ext1/handlers.py
+++ b/examples/simple/simple_ext1/handlers.py
@@ -18,7 +18,8 @@ def get(self):
         self.log.info(f"Extension Name in {self.name} Default Handler: {self.name}")
         # A method for getting the url to static files (prefixed with /static/<name>).
         self.log.info(
-            "Static URL for / in simple_ext1 Default Handler: {}".format(self.static_url(path="/"))
+            "Static URL for / in simple_ext1 Default Handler: %s",
+            self.static_url(path="/"),
         )
         self.write("<h1>Hello Simple 1 - I am the default...</h1>")
         self.write(f"Config in {self.name} Default Handler: {self.config}")
diff --git a/jupyter_server/_version.py b/jupyter_server/_version.py
index fa814fbb2f..b5b33991ed 100644
--- a/jupyter_server/_version.py
+++ b/jupyter_server/_version.py
@@ -4,16 +4,15 @@
 """
 
 import re
-from typing import List
 
 # Version string must appear intact for automatic versioning
-__version__ = "2.15.0.dev0"
+__version__ = "2.16.0.dev0"
 
 # Build up version_info tuple for backwards compatibility
 pattern = r"(?P<major>\d+).(?P<minor>\d+).(?P<patch>\d+)(?P<rest>.*)"
 match = re.match(pattern, __version__)
 assert match is not None
-parts: List[object] = [int(match[part]) for part in ["major", "minor", "patch"]]
+parts: list[object] = [int(match[part]) for part in ["major", "minor", "patch"]]
 if match["rest"]:
     parts.append(match["rest"])
 version_info = tuple(parts)
diff --git a/jupyter_server/auth/authorizer.py b/jupyter_server/auth/authorizer.py
index 10414e2c39..fcebc3404b 100644
--- a/jupyter_server/auth/authorizer.py
+++ b/jupyter_server/auth/authorizer.py
@@ -10,7 +10,7 @@
 # Distributed under the terms of the Modified BSD License.
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Awaitable
+from typing import TYPE_CHECKING
 
 from traitlets import Instance
 from traitlets.config import LoggingConfigurable
@@ -18,6 +18,8 @@
 from .identity import IdentityProvider, User
 
 if TYPE_CHECKING:
+    from collections.abc import Awaitable
+
     from jupyter_server.base.handlers import JupyterHandler
 
 
diff --git a/jupyter_server/base/call_context.py b/jupyter_server/base/call_context.py
index cf71256235..4e80be8a7d 100644
--- a/jupyter_server/base/call_context.py
+++ b/jupyter_server/base/call_context.py
@@ -3,7 +3,7 @@
 # Distributed under the terms of the Modified BSD License.
 
 from contextvars import Context, ContextVar, copy_context
-from typing import Any, Dict, List
+from typing import Any
 
 
 class CallContext:
@@ -22,7 +22,7 @@ class CallContext:
     # easier management over maintaining a set of ContextVar instances, since the Context is a
     # map of ContextVar instances to their values, and the "name" is no longer a lookup key.
     _NAME_VALUE_MAP = "_name_value_map"
-    _name_value_map: ContextVar[Dict[str, Any]] = ContextVar(_NAME_VALUE_MAP)
+    _name_value_map: ContextVar[dict[str, Any]] = ContextVar(_NAME_VALUE_MAP)
 
     @classmethod
     def get(cls, name: str) -> Any:
@@ -65,7 +65,7 @@ def set(cls, name: str, value: Any) -> None:
         name_value_map[name] = value
 
     @classmethod
-    def context_variable_names(cls) -> List[str]:
+    def context_variable_names(cls) -> list[str]:
         """Returns a list of variable names set for this call context.
 
         Returns
@@ -77,7 +77,7 @@ def context_variable_names(cls) -> List[str]:
         return list(name_value_map.keys())
 
     @classmethod
-    def _get_map(cls) -> Dict[str, Any]:
+    def _get_map(cls) -> dict[str, Any]:
         """Get the map of names to their values from the _NAME_VALUE_MAP context var.
 
         If the map does not exist in the current context, an empty map is created and returned.
diff --git a/jupyter_server/base/handlers.py b/jupyter_server/base/handlers.py
index 9a47b2f68c..3909c70638 100644
--- a/jupyter_server/base/handlers.py
+++ b/jupyter_server/base/handlers.py
@@ -13,9 +13,10 @@
 import re
 import types
 import warnings
+from collections.abc import Awaitable, Coroutine, Sequence
 from http.client import responses
 from logging import Logger
-from typing import TYPE_CHECKING, Any, Awaitable, Coroutine, Sequence, cast
+from typing import TYPE_CHECKING, Any, cast
 from urllib.parse import urlparse
 
 import prometheus_client
diff --git a/jupyter_server/config_manager.py b/jupyter_server/config_manager.py
index 4a0bff4015..8f49cb7bd6 100644
--- a/jupyter_server/config_manager.py
+++ b/jupyter_server/config_manager.py
@@ -14,7 +14,7 @@
 from traitlets.config import LoggingConfigurable
 from traitlets.traitlets import Bool, Unicode
 
-StrDict = t.Dict[str, t.Any]
+StrDict = dict[str, t.Any]
 
 
 def recursive_update(target: StrDict, new: StrDict) -> None:
diff --git a/jupyter_server/event_schemas/contents_service/v1.yaml b/jupyter_server/event_schemas/contents_service/v1.yaml
index a787f9b2b0..d049005e01 100644
--- a/jupyter_server/event_schemas/contents_service/v1.yaml
+++ b/jupyter_server/event_schemas/contents_service/v1.yaml
@@ -1,5 +1,5 @@
 "$id": https://events.jupyter.org/jupyter_server/contents_service/v1
-version: 1
+version: "1"
 title: Contents Manager activities
 personal-data: true
 description: |
diff --git a/jupyter_server/event_schemas/gateway_client/v1.yaml b/jupyter_server/event_schemas/gateway_client/v1.yaml
index 0a35d2464d..0257ce071a 100644
--- a/jupyter_server/event_schemas/gateway_client/v1.yaml
+++ b/jupyter_server/event_schemas/gateway_client/v1.yaml
@@ -1,5 +1,5 @@
 "$id": https://events.jupyter.org/jupyter_server/gateway_client/v1
-version: 1
+version: "1"
 title: Gateway Client activities.
 personal-data: true
 description: |
diff --git a/jupyter_server/event_schemas/kernel_actions/v1.yaml b/jupyter_server/event_schemas/kernel_actions/v1.yaml
index e0375e5aaa..66c13802c2 100644
--- a/jupyter_server/event_schemas/kernel_actions/v1.yaml
+++ b/jupyter_server/event_schemas/kernel_actions/v1.yaml
@@ -1,5 +1,5 @@
 "$id": https://events.jupyter.org/jupyter_server/kernel_actions/v1
-version: 1
+version: "1"
 title: Kernel Manager activities
 personal-data: true
 description: |
diff --git a/jupyter_server/extension/handler.py b/jupyter_server/extension/handler.py
index 31377cc367..4285c415b0 100644
--- a/jupyter_server/extension/handler.py
+++ b/jupyter_server/extension/handler.py
@@ -5,6 +5,7 @@
 from logging import Logger
 from typing import TYPE_CHECKING, Any, cast
 
+from jinja2 import Template
 from jinja2.exceptions import TemplateNotFound
 
 from jupyter_server.base.handlers import FileFindHandler
@@ -21,13 +22,14 @@ class ExtensionHandlerJinjaMixin:
     template rendering.
     """
 
-    def get_template(self, name: str) -> str:
+    def get_template(self, name: str) -> Template:
         """Return the jinja template object for a given name"""
         try:
             env = f"{self.name}_jinja2_env"  # type:ignore[attr-defined]
-            return cast(str, self.settings[env].get_template(name))  # type:ignore[attr-defined]
+            template = cast(Template, self.settings[env].get_template(name))  # type:ignore[attr-defined]
+            return template
         except TemplateNotFound:
-            return cast(str, super().get_template(name))  # type:ignore[misc]
+            return cast(Template, super().get_template(name))  # type:ignore[misc]
 
 
 class ExtensionHandlerMixin:
@@ -81,6 +83,20 @@ def server_config(self) -> Config:
     def base_url(self) -> str:
         return cast(str, self.settings.get("base_url", "/"))
 
+    def render_template(self, name: str, **ns) -> str:
+        """Override render template to handle static_paths
+
+        If render_template is called with a template from the base environment
+        (e.g. default error pages)
+        make sure our extension-specific static_url is _not_ used.
+        """
+        template = cast(Template, self.get_template(name))  # type:ignore[attr-defined]
+        ns.update(self.template_namespace)  # type:ignore[attr-defined]
+        if template.environment is self.settings["jinja2_env"]:
+            # default template environment, use default static_url
+            ns["static_url"] = super().static_url  # type:ignore[misc]
+        return cast(str, template.render(**ns))
+
     @property
     def static_url_prefix(self) -> str:
         return self.extensionapp.static_url_prefix
diff --git a/jupyter_server/extension/serverextension.py b/jupyter_server/extension/serverextension.py
index b4c9dacbc2..5978933acb 100644
--- a/jupyter_server/extension/serverextension.py
+++ b/jupyter_server/extension/serverextension.py
@@ -276,7 +276,7 @@ def toggle_server_extension(self, import_name: str) -> None:
             # If successful, let's log.
             self.log.info(f"    - Extension successfully {self._toggle_post_message}.")
         except Exception as err:
-            self.log.info(f"     {RED_X} Validation failed: {err}")
+            self.log.error(f"     {RED_X} Validation failed: {err}")
 
     def start(self) -> None:
         """Perform the App's actions as configured"""
@@ -336,7 +336,7 @@ def list_server_extensions(self) -> None:
 
         for option in configurations:
             config_dir = _get_config_dir(**option)
-            self.log.info(f"Config dir: {config_dir}")
+            print(f"Config dir: {config_dir}")
             write_dir = "jupyter_server_config.d"
             config_manager = ExtensionConfigManager(
                 read_config_path=[config_dir],
@@ -345,20 +345,18 @@ def list_server_extensions(self) -> None:
             jpserver_extensions = config_manager.get_jpserver_extensions()
             for name, enabled in jpserver_extensions.items():
                 # Attempt to get extension metadata
-                self.log.info(f"    {name} {GREEN_ENABLED if enabled else RED_DISABLED}")
+                print(f"    {name} {GREEN_ENABLED if enabled else RED_DISABLED}")
                 try:
-                    self.log.info(f"    - Validating {name}...")
+                    print(f"    - Validating {name}...")
                     extension = ExtensionPackage(name=name, enabled=enabled)
                     if not extension.validate():
                         msg = "validation failed"
                         raise ValueError(msg)
                     version = extension.version
-                    self.log.info(f"      {name} {version} {GREEN_OK}")
+                    print(f"      {name} {version} {GREEN_OK}")
                 except Exception as err:
-                    exc_info = False
-                    if int(self.log_level) <= logging.DEBUG:  # type:ignore[call-overload]
-                        exc_info = True
-                    self.log.warning(f"      {RED_X} {err}", exc_info=exc_info)
+                    self.log.debug("", exc_info=True)
+                    print(f"      {RED_X} {err}")
             # Add a blank line between paths.
             self.log.info("")
 
diff --git a/jupyter_server/files/handlers.py b/jupyter_server/files/handlers.py
index 2c1dc5adf6..749328438e 100644
--- a/jupyter_server/files/handlers.py
+++ b/jupyter_server/files/handlers.py
@@ -6,7 +6,7 @@
 
 import mimetypes
 from base64 import decodebytes
-from typing import Awaitable
+from typing import TYPE_CHECKING
 
 from jupyter_core.utils import ensure_async
 from tornado import web
@@ -14,6 +14,9 @@
 from jupyter_server.auth.decorator import authorized
 from jupyter_server.base.handlers import JupyterHandler
 
+if TYPE_CHECKING:
+    from collections.abc import Awaitable
+
 AUTH_RESOURCE = "contents"
 
 
diff --git a/jupyter_server/gateway/managers.py b/jupyter_server/gateway/managers.py
index 0ac47f8f57..daa6f99213 100644
--- a/jupyter_server/gateway/managers.py
+++ b/jupyter_server/gateway/managers.py
@@ -632,9 +632,10 @@ async def get_msg(self, *args: Any, **kwargs: Any) -> dict[str, Any]:
         timeout = kwargs.get("timeout", 1)
         msg = await self._async_get(timeout=timeout)
         self.log.debug(
-            "Received message on channel: {}, msg_id: {}, msg_type: {}".format(
-                self.channel_name, msg["msg_id"], msg["msg_type"] if msg else "null"
-            )
+            "Received message on channel: %s, msg_id: %s, msg_type: %s",
+            self.channel_name,
+            msg["msg_id"],
+            msg["msg_type"] if msg else "null",
         )
         self.task_done()
         return cast("dict[str, Any]", msg)
@@ -643,9 +644,10 @@ def send(self, msg: dict[str, Any]) -> None:
         """Send a message to the queue."""
         message = json.dumps(msg, default=ChannelQueue.serialize_datetime).replace("</", "<\\/")
         self.log.debug(
-            "Sending message on channel: {}, msg_id: {}, msg_type: {}".format(
-                self.channel_name, msg["msg_id"], msg["msg_type"] if msg else "null"
-            )
+            "Sending message on channel: %s, msg_id: %s, msg_type: %s",
+            self.channel_name,
+            msg["msg_id"],
+            msg["msg_type"] if msg else "null",
         )
         self.channel_socket.send(message)
 
diff --git a/jupyter_server/log.py b/jupyter_server/log.py
index aed024bb32..b1211114e9 100644
--- a/jupyter_server/log.py
+++ b/jupyter_server/log.py
@@ -41,13 +41,16 @@ def _scrub_uri(uri: str) -> str:
     return uri
 
 
-def log_request(handler):
+def log_request(handler, record_prometheus_metrics=True):
     """log a bit more information about each request than tornado's default
 
     - move static file get success to debug-level (reduces noise)
     - get proxied IP instead of proxy IP
     - log referer for redirect and failed requests
     - log user-agent for failed requests
+
+    if record_prometheus_metrics is true, will record a histogram prometheus
+    metric (http_request_duration_seconds) for each request handler
     """
     status = handler.get_status()
     request = handler.request
@@ -97,4 +100,5 @@ def log_request(handler):
                 headers[header] = request.headers[header]
         log_method(json.dumps(headers, indent=2))
     log_method(msg.format(**ns))
-    prometheus_log_method(handler)
+    if record_prometheus_metrics:
+        prometheus_log_method(handler)
diff --git a/jupyter_server/prometheus/metrics.py b/jupyter_server/prometheus/metrics.py
index 1a02f86209..c0aeb37568 100644
--- a/jupyter_server/prometheus/metrics.py
+++ b/jupyter_server/prometheus/metrics.py
@@ -5,19 +5,35 @@
 conventions for metrics & labels.
 """
 
+from prometheus_client import Gauge, Histogram, Info
+
+from jupyter_server._version import version_info as server_version_info
+
 try:
-    # Jupyter Notebook also defines these metrics.  Re-defining them results in a ValueError.
-    # Try to de-duplicate by using the ones in Notebook if available.
+    from notebook._version import version_info as notebook_version_info
+except ImportError:
+    notebook_version_info = None
+
+
+if (
+    notebook_version_info is not None  # No notebook package found
+    and notebook_version_info < (7,)  # Notebook package found, is version 6
+    # Notebook package found, but its version is the same as jupyter_server
+    # version. This means some package (looking at you, nbclassic) has shimmed
+    # the notebook package to instead be imports from the jupyter_server package.
+    # In such cases, notebook.prometheus.metrics is actually *this file*, so
+    # trying to import it will cause a circular import. So we don't.
+    and notebook_version_info != server_version_info
+):
+    # Jupyter Notebook v6 also defined these metrics.  Re-defining them results in a ValueError,
+    # so we simply re-export them if we are co-existing with the notebook v6 package.
     # See https://github.com/jupyter/jupyter_server/issues/209
     from notebook.prometheus.metrics import (
         HTTP_REQUEST_DURATION_SECONDS,
         KERNEL_CURRENTLY_RUNNING_TOTAL,
         TERMINAL_CURRENTLY_RUNNING_TOTAL,
     )
-
-except ImportError:
-    from prometheus_client import Gauge, Histogram
-
+else:
     HTTP_REQUEST_DURATION_SECONDS = Histogram(
         "http_request_duration_seconds",
         "duration in seconds for all HTTP requests",
@@ -35,9 +51,28 @@
         ["type"],
     )
 
+# New prometheus metrics that do not exist in notebook v6 go here
+SERVER_INFO = Info("jupyter_server", "Jupyter Server Version information")
+SERVER_EXTENSION_INFO = Info(
+    "jupyter_server_extension",
+    "Jupyter Server Extensiom Version Information",
+    ["name", "version", "enabled"],
+)
+LAST_ACTIVITY = Gauge(
+    "jupyter_server_last_activity_timestamp_seconds",
+    "Timestamp of last seen activity on this Jupyter Server",
+)
+SERVER_STARTED = Gauge(
+    "jupyter_server_started_timestamp_seconds", "Timestamp of when this Jupyter Server was started"
+)
+ACTIVE_DURATION = Gauge(
+    "jupyter_server_active_duration_seconds",
+    "Number of seconds this Jupyter Server has been active",
+)
 
 __all__ = [
     "HTTP_REQUEST_DURATION_SECONDS",
     "TERMINAL_CURRENTLY_RUNNING_TOTAL",
     "KERNEL_CURRENTLY_RUNNING_TOTAL",
+    "SERVER_INFO",
 ]
diff --git a/jupyter_server/serverapp.py b/jupyter_server/serverapp.py
index 3dedd5634f..8aa3dbd082 100644
--- a/jupyter_server/serverapp.py
+++ b/jupyter_server/serverapp.py
@@ -28,6 +28,7 @@
 import urllib
 import warnings
 from base64 import encodebytes
+from functools import partial
 from pathlib import Path
 
 import jupyter_client
@@ -110,6 +111,13 @@
     GatewaySessionManager,
 )
 from jupyter_server.log import log_request
+from jupyter_server.prometheus.metrics import (
+    ACTIVE_DURATION,
+    LAST_ACTIVITY,
+    SERVER_EXTENSION_INFO,
+    SERVER_INFO,
+    SERVER_STARTED,
+)
 from jupyter_server.services.config import ConfigManager
 from jupyter_server.services.contents.filemanager import (
     AsyncFileContentsManager,
@@ -403,7 +411,9 @@ def init_settings(
 
         settings = {
             # basics
-            "log_function": log_request,
+            "log_function": partial(
+                log_request, record_prometheus_metrics=jupyter_app.record_http_request_metrics
+            ),
             "base_url": base_url,
             "default_url": default_url,
             "template_path": template_path,
@@ -1986,6 +1996,18 @@ def _default_terminals_enabled(self) -> bool:
         config=True,
     )
 
+    record_http_request_metrics = Bool(
+        True,
+        help="""
+        Record http_request_duration_seconds metric in the metrics endpoint.
+
+        Since a histogram is exposed for each request handler, this can create a
+        *lot* of metrics, creating operational challenges for multitenant deployments.
+
+        Set to False to disable recording the http_request_duration_seconds metric.
+        """,
+    )
+
     static_immutable_cache = List(
         Unicode(),
         help="""
@@ -2388,7 +2410,14 @@ def init_signal(self) -> None:
             signal.signal(signal.SIGINFO, self._signal_info)
 
     def _handle_sigint(self, sig: t.Any, frame: t.Any) -> None:
-        """SIGINT handler spawns confirmation dialog"""
+        """SIGINT handler spawns confirmation dialog
+
+        Note:
+            JupyterHub replaces this method with _signal_stop
+            in order to bypass the interactive prompt.
+            https://github.com/jupyterhub/jupyterhub/pull/4864
+
+        """
         # register more forceful signal handler for ^C^C case
         signal.signal(signal.SIGINT, self._signal_stop)
         # request confirmation dialog in bg thread, to avoid
@@ -2446,7 +2475,13 @@ def _confirm_exit(self) -> None:
         self.io_loop.add_callback_from_signal(self._restore_sigint_handler)
 
     def _signal_stop(self, sig: t.Any, frame: t.Any) -> None:
-        """Handle a stop signal."""
+        """Handle a stop signal.
+
+        Note:
+            JupyterHub configures this method to be called for SIGINT.
+            https://github.com/jupyterhub/jupyterhub/pull/4864
+
+        """
         self.log.critical(_i18n("received signal %s, stopping"), sig)
         self.stop(from_signal=True)
 
@@ -2517,8 +2552,6 @@ def init_mime_overrides(self) -> None:
         # ensure css, js are correct, which are required for pages to function
         mimetypes.add_type("text/css", ".css")
         mimetypes.add_type("application/javascript", ".js")
-        # for python <3.8
-        mimetypes.add_type("application/wasm", ".wasm")
 
     def shutdown_no_activity(self) -> None:
         """Shutdown server on timeout when there are no kernels or terminals."""
@@ -2683,7 +2716,7 @@ def _init_asyncio_patch() -> None:
         at least until asyncio adds *_reader methods
         to proactor.
         """
-        if sys.platform.startswith("win") and sys.version_info >= (3, 8):
+        if sys.platform.startswith("win"):
             import asyncio
 
             try:
@@ -2696,6 +2729,27 @@ def _init_asyncio_patch() -> None:
                     # prefer Selector to Proactor for tornado + pyzmq
                     asyncio.set_event_loop_policy(WindowsSelectorEventLoopPolicy())
 
+    def init_metrics(self) -> None:
+        """
+        Initialize any prometheus metrics that need to be set up on server startup
+        """
+        SERVER_INFO.info({"version": __version__})
+
+        for ext in self.extension_manager.extensions.values():
+            SERVER_EXTENSION_INFO.labels(
+                name=ext.name, version=ext.version, enabled=str(ext.enabled).lower()
+            )
+
+        started = self.web_app.settings["started"]
+        SERVER_STARTED.set(started.timestamp())
+
+        LAST_ACTIVITY.set_function(lambda: self.web_app.last_activity().timestamp())
+        ACTIVE_DURATION.set_function(
+            lambda: (
+                self.web_app.last_activity() - self.web_app.settings["started"]
+            ).total_seconds()
+        )
+
     @catch_config_error
     def initialize(
         self,
@@ -2724,7 +2778,11 @@ def initialize(
         self._init_asyncio_patch()
         # Parse command line, load ServerApp config files,
         # and update ServerApp config.
+        # preserve jpserver_extensions, which may have been set by starter_extension
+        # don't let config clobber this value
+        jpserver_extensions = self.jpserver_extensions.copy()
         super().initialize(argv=argv)
+        self.jpserver_extensions.update(jpserver_extensions)
         if self._dispatching:
             return
         # initialize io loop as early as possible,
@@ -2759,6 +2817,7 @@ def initialize(
         self.load_server_extensions()
         self.init_mime_overrides()
         self.init_shutdown_no_activity()
+        self.init_metrics()
         if new_httpserver:
             self.init_httpserver()
 
diff --git a/jupyter_server/services/api/handlers.py b/jupyter_server/services/api/handlers.py
index 22904fdb07..f61d9dd10f 100644
--- a/jupyter_server/services/api/handlers.py
+++ b/jupyter_server/services/api/handlers.py
@@ -4,7 +4,7 @@
 # Distributed under the terms of the Modified BSD License.
 import json
 import os
-from typing import Any, Dict, List
+from typing import Any
 
 from jupyter_core.utils import ensure_async
 from tornado import web
@@ -87,7 +87,7 @@ async def get(self):
         else:
             permissions_to_check = {}
 
-        permissions: Dict[str, List[str]] = {}
+        permissions: dict[str, list[str]] = {}
         user = self.current_user
 
         for resource, actions in permissions_to_check.items():
@@ -106,7 +106,7 @@ async def get(self):
                 if authorized:
                     allowed.append(action)
 
-        identity: Dict[str, Any] = self.identity_provider.identity_model(user)
+        identity: dict[str, Any] = self.identity_provider.identity_model(user)
         model = {
             "identity": identity,
             "permissions": permissions,
diff --git a/jupyter_server/services/config/manager.py b/jupyter_server/services/config/manager.py
index d4e207e247..223d4fed2c 100644
--- a/jupyter_server/services/config/manager.py
+++ b/jupyter_server/services/config/manager.py
@@ -23,7 +23,7 @@ class ConfigManager(LoggingConfigurable):
 
     def get(self, section_name):
         """Get the config from all config sections."""
-        config: t.Dict[str, t.Any] = {}
+        config: dict[str, t.Any] = {}
         # step through back to front, to ensure front of the list is top priority
         for p in self.read_config_path[::-1]:
             cm = BaseJSONConfigManager(config_dir=p)
diff --git a/jupyter_server/services/contents/handlers.py b/jupyter_server/services/contents/handlers.py
index 13e987809b..ae160e6707 100644
--- a/jupyter_server/services/contents/handlers.py
+++ b/jupyter_server/services/contents/handlers.py
@@ -7,7 +7,7 @@
 # Distributed under the terms of the Modified BSD License.
 import json
 from http import HTTPStatus
-from typing import Any, Dict, List
+from typing import Any
 
 try:
     from jupyter_client.jsonutil import json_default
@@ -24,7 +24,7 @@
 AUTH_RESOURCE = "contents"
 
 
-def _validate_keys(expect_defined: bool, model: Dict[str, Any], keys: List[str]):
+def _validate_keys(expect_defined: bool, model: dict[str, Any], keys: list[str]):
     """
     Validate that the keys are defined (i.e. not None) or not (i.e. None)
     """
@@ -210,10 +210,9 @@ async def patch(self, path=""):
     async def _copy(self, copy_from, copy_to=None):
         """Copy a file, optionally specifying a target directory."""
         self.log.info(
-            "Copying {copy_from} to {copy_to}".format(
-                copy_from=copy_from,
-                copy_to=copy_to or "",
-            )
+            "Copying %r to %r",
+            copy_from,
+            copy_to or "",
         )
         model = await ensure_async(self.contents_manager.copy(copy_from, copy_to))
         self.set_status(201)
diff --git a/jupyter_server/services/events/handlers.py b/jupyter_server/services/events/handlers.py
index 82265ae0e4..fbc007341d 100644
--- a/jupyter_server/services/events/handlers.py
+++ b/jupyter_server/services/events/handlers.py
@@ -7,7 +7,7 @@
 
 import json
 from datetime import datetime
-from typing import TYPE_CHECKING, Any, Dict, Optional, cast
+from typing import TYPE_CHECKING, Any, Optional, cast
 
 from jupyter_core.utils import ensure_async
 from tornado import web, websocket
@@ -71,12 +71,25 @@ def on_close(self):
         self.event_logger.remove_listener(listener=self.event_listener)
 
 
-def validate_model(data: dict[str, Any]) -> None:
-    """Validates for required fields in the JSON request body"""
+def validate_model(
+    data: dict[str, Any], registry: jupyter_events.schema_registry.SchemaRegistry
+) -> None:
+    """Validates for required fields in the JSON request body and verifies that
+    a registered schema/version exists"""
     required_keys = {"schema_id", "version", "data"}
     for key in required_keys:
         if key not in data:
-            raise web.HTTPError(400, f"Missing `{key}` in the JSON request body.")
+            message = f"Missing `{key}` in the JSON request body."
+            raise Exception(message)
+    schema_id = cast(str, data.get("schema_id"))
+    # The case where a given schema_id isn't found,
+    # jupyter_events raises a useful error, so there's no need to
+    # handle that case here.
+    schema = registry.get(schema_id)
+    version = str(cast(str, data.get("version")))
+    if schema.version != version:
+        message = f"Unregistered version: {version!r}≠{schema.version!r} for `{schema_id}`"
+        raise Exception(message)
 
 
 def get_timestamp(data: dict[str, Any]) -> Optional[datetime]:
@@ -111,18 +124,18 @@ async def post(self):
             raise web.HTTPError(400, "No JSON data provided")
 
         try:
-            validate_model(payload)
+            validate_model(payload, self.event_logger.schemas)
             self.event_logger.emit(
                 schema_id=cast(str, payload.get("schema_id")),
-                data=cast("Dict[str, Any]", payload.get("data")),
+                data=cast("dict[str, Any]", payload.get("data")),
                 timestamp_override=get_timestamp(payload),
             )
             self.set_status(204)
             self.finish()
-        except web.HTTPError:
-            raise
         except Exception as e:
-            raise web.HTTPError(500, str(e)) from e
+            # All known exceptions are raised by bad requests, e.g., bad
+            # version, unregistered schema, invalid emission data payload, etc.
+            raise web.HTTPError(400, str(e)) from e
 
 
 default_handlers = [
diff --git a/jupyter_server/services/kernels/connection/abc.py b/jupyter_server/services/kernels/connection/abc.py
index 71f9e8254f..61e11a948e 100644
--- a/jupyter_server/services/kernels/connection/abc.py
+++ b/jupyter_server/services/kernels/connection/abc.py
@@ -1,5 +1,5 @@
 from abc import ABC, abstractmethod
-from typing import Any, List
+from typing import Any
 
 
 class KernelWebsocketConnectionABC(ABC):
@@ -25,5 +25,5 @@ def handle_incoming_message(self, incoming_msg: str) -> None:
         """Broker the incoming websocket message to the appropriate ZMQ channel."""
 
     @abstractmethod
-    def handle_outgoing_message(self, stream: str, outgoing_msg: List[Any]) -> None:
+    def handle_outgoing_message(self, stream: str, outgoing_msg: list[Any]) -> None:
         """Broker outgoing ZMQ messages to the kernel websocket."""
diff --git a/jupyter_server/services/kernels/connection/base.py b/jupyter_server/services/kernels/connection/base.py
index a0e0bae8b8..6af10444b5 100644
--- a/jupyter_server/services/kernels/connection/base.py
+++ b/jupyter_server/services/kernels/connection/base.py
@@ -2,7 +2,7 @@
 
 import json
 import struct
-from typing import Any, List
+from typing import Any
 
 from jupyter_client.session import Session
 from tornado.websocket import WebSocketHandler
@@ -89,7 +89,7 @@ def serialize_msg_to_ws_v1(msg_or_list, channel, pack=None):
     else:
         msg_list = msg_or_list
     channel = channel.encode("utf-8")
-    offsets: List[Any] = []
+    offsets: list[Any] = []
     offsets.append(8 * (1 + 1 + len(msg_list) + 1))
     offsets.append(len(channel) + offsets[-1])
     for msg in msg_list:
@@ -173,7 +173,7 @@ def handle_incoming_message(self, incoming_msg: str) -> None:
         """Handle an incoming message."""
         raise NotImplementedError
 
-    def handle_outgoing_message(self, stream: str, outgoing_msg: List[Any]) -> None:
+    def handle_outgoing_message(self, stream: str, outgoing_msg: list[Any]) -> None:
         """Handle an outgoing message."""
         raise NotImplementedError
 
diff --git a/jupyter_server/services/sessions/handlers.py b/jupyter_server/services/sessions/handlers.py
index 3e013c0335..2d62c21b5a 100644
--- a/jupyter_server/services/sessions/handlers.py
+++ b/jupyter_server/services/sessions/handlers.py
@@ -161,14 +161,30 @@ async def patch(self, session_id):
                 changes["kernel_id"] = kernel_id
             elif model["kernel"].get("name") is not None:
                 kernel_name = model["kernel"]["name"]
-                kernel_id = await sm.start_kernel_for_session(
-                    session_id,
-                    kernel_name=kernel_name,
-                    name=before["name"],
-                    path=before["path"],
-                    type=before["type"],
-                )
-                changes["kernel_id"] = kernel_id
+
+                try:
+                    kernel_id = await sm.start_kernel_for_session(
+                        session_id,
+                        kernel_name=kernel_name,
+                        name=before["name"],
+                        path=before["path"],
+                        type=before["type"],
+                    )
+                    changes["kernel_id"] = kernel_id
+                except Exception as e:
+                    # the error message may contain sensitive information, so we want to
+                    # be careful with it, thus we only give the short repr of the exception
+                    # and the full traceback.
+                    # this should be fine as we are exposing here the same info as when we start a new kernel
+                    msg = "The '%s' kernel could not be started: %s" % (
+                        kernel_name,
+                        repr(str(e)),
+                    )
+                    status_msg = "Error starting kernel %s" % kernel_name
+                    self.log.error("Error starting kernel: %s", kernel_name)
+                    self.set_status(501)
+                    self.finish(json.dumps({"message": msg, "short_message": status_msg}))
+                    return
 
         await sm.update_session(session_id, **changes)
         s_model = await sm.get_session(session_id=session_id)
diff --git a/jupyter_server/services/sessions/sessionmanager.py b/jupyter_server/services/sessions/sessionmanager.py
index 8b392b4e1b..3aac78a0a9 100644
--- a/jupyter_server/services/sessions/sessionmanager.py
+++ b/jupyter_server/services/sessions/sessionmanager.py
@@ -5,7 +5,7 @@
 import os
 import pathlib
 import uuid
-from typing import Any, Dict, List, NewType, Optional, Union, cast
+from typing import Any, NewType, Optional, Union, cast
 
 KernelName = NewType("KernelName", str)
 ModelName = NewType("ModelName", str)
@@ -100,7 +100,7 @@ class KernelSessionRecordList:
     it will be appended.
     """
 
-    _records: List[KernelSessionRecord]
+    _records: list[KernelSessionRecord]
 
     def __init__(self, *records: KernelSessionRecord):
         """Initialize a record list."""
@@ -267,7 +267,7 @@ async def create_session(
         type: Optional[str] = None,
         kernel_name: Optional[KernelName] = None,
         kernel_id: Optional[str] = None,
-    ) -> Dict[str, Any]:
+    ) -> dict[str, Any]:
         """Creates a session and returns its model
 
         Parameters
@@ -291,11 +291,11 @@ async def create_session(
             session_id, path=path, name=name, type=type, kernel_id=kernel_id
         )
         self._pending_sessions.remove(record)
-        return cast(Dict[str, Any], result)
+        return cast(dict[str, Any], result)
 
     def get_kernel_env(
         self, path: Optional[str], name: Optional[ModelName] = None
-    ) -> Dict[str, str]:
+    ) -> dict[str, str]:
         """Return the environment variables that need to be set in the kernel
 
         Parameters
diff --git a/jupyter_server/utils.py b/jupyter_server/utils.py
index 0c987bff25..d83e1be880 100644
--- a/jupyter_server/utils.py
+++ b/jupyter_server/utils.py
@@ -13,7 +13,7 @@
 from _frozen_importlib_external import _NamespacePath
 from contextlib import contextmanager
 from pathlib import Path
-from typing import Any, Generator, NewType, Sequence
+from typing import TYPE_CHECKING, Any, NewType
 from urllib.parse import (
     SplitResult,
     quote,
@@ -32,6 +32,9 @@
 from tornado.httpclient import AsyncHTTPClient, HTTPClient, HTTPRequest, HTTPResponse
 from tornado.netutil import Resolver
 
+if TYPE_CHECKING:
+    from collections.abc import Generator, Sequence
+
 ApiPath = NewType("ApiPath", str)
 
 # Re-export
@@ -378,17 +381,9 @@ def filefind(filename: str, path_dirs: Sequence[str]) -> str:
         # os.path.abspath resolves '..', but Path.absolute() doesn't
         # Path.resolve() does, but traverses symlinks, which we don't want
         test_path = Path(os.path.abspath(test_path))
-        if sys.version_info >= (3, 9):
-            if not test_path.is_relative_to(path):
-                # points outside root, e.g. via `filename='../foo'`
-                continue
-        else:
-            # is_relative_to is new in 3.9
-            try:
-                test_path.relative_to(path)
-            except ValueError:
-                # points outside root, e.g. via `filename='../foo'`
-                continue
+        if not test_path.is_relative_to(path):
+            # points outside root, e.g. via `filename='../foo'`
+            continue
         # make sure we don't call is_file before we know it's a file within a prefix
         # GHSA-hrw6-wg82-cm62 - can leak password hash on windows.
         if test_path.is_file():
diff --git a/pyproject.toml b/pyproject.toml
index 9bfcc74eef..e04983380d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -21,7 +21,7 @@ classifiers = [
     "Programming Language :: Python :: 3",
     "Programming Language :: Python :: 3 :: Only",
 ]
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 dependencies = [
     "anyio>=3.1.0",
     "argon2-cffi>=21.1",
@@ -40,14 +40,14 @@ dependencies = [
     "tornado>=6.2.0",
     "traitlets>=5.6.0",
     "websocket-client>=1.7",
-    "jupyter_events>=0.9.0",
+    "jupyter_events>=0.11.0",
     "overrides>=5.0"
 ]
 
 [project.urls]
 Homepage = "https://jupyter-server.readthedocs.io"
 Documentation = "https://jupyter-server.readthedocs.io"
-Funding = "https://numfocus.org/donate"
+Funding = "https://jupyter.org/about#donate"
 Source = "https://github.com/jupyter-server/jupyter_server"
 Tracker = "https://github.com/jupyter-server/jupyter_server/issues"
 
@@ -142,6 +142,7 @@ extend-select = [
   "B",  # flake8-bugbear
   "I",  # isort
   "UP",  # pyupgrade
+  "G001", # no % or f formatting in logs, prevents sttructured logging
 ]
 unfixable = [
   # Don't touch print statements
@@ -178,7 +179,10 @@ filterwarnings = [
   "error",
   "ignore:datetime.datetime.utc:DeprecationWarning",
   "module:add_callback_from_signal is deprecated:DeprecationWarning",
-  "ignore::jupyter_server.utils.JupyterServerAuthWarning"
+  "ignore::jupyter_server.utils.JupyterServerAuthWarning",
+
+  # ignore unclosed sqlite in traits
+  "ignore:unclosed database in <sqlite3.Connection:ResourceWarning",
 ]
 
 [tool.coverage.report]
@@ -208,7 +212,7 @@ pydist_resource_paths = ["jupyter_server/static/style/bootstrap.min.css", "jupyt
 post-version-spec = "dev"
 
 [tool.mypy]
-python_version = "3.8"
+python_version = "3.9"
 explicit_package_bases = true
 strict = true
 pretty = true
diff --git a/tests/auth/test_authorizer.py b/tests/auth/test_authorizer.py
index 3ba6bef9f1..59a6aa7428 100644
--- a/tests/auth/test_authorizer.py
+++ b/tests/auth/test_authorizer.py
@@ -3,7 +3,7 @@
 import asyncio
 import json
 import os
-from typing import Awaitable
+from collections.abc import Awaitable
 
 import pytest
 from jupyter_client.kernelspec import NATIVE_KERNEL_NAME
diff --git a/tests/extension/mockextensions/__init__.py b/tests/extension/mockextensions/__init__.py
index a25d9fc670..2c01cfe266 100644
--- a/tests/extension/mockextensions/__init__.py
+++ b/tests/extension/mockextensions/__init__.py
@@ -2,7 +2,7 @@
 to load in various tests.
 """
 
-from .app import MockExtensionApp
+from .app import MockExtensionApp, MockExtensionNoTemplateApp
 
 
 # Function that makes these extensions discoverable
@@ -13,6 +13,10 @@ def _jupyter_server_extension_points():
             "module": "tests.extension.mockextensions.app",
             "app": MockExtensionApp,
         },
+        {
+            "module": "tests.extension.mockextensions.app",
+            "app": MockExtensionNoTemplateApp,
+        },
         {"module": "tests.extension.mockextensions.mock1"},
         {"module": "tests.extension.mockextensions.mock2"},
         {"module": "tests.extension.mockextensions.mock3"},
diff --git a/tests/extension/mockextensions/app.py b/tests/extension/mockextensions/app.py
index 26f38464cd..5546195593 100644
--- a/tests/extension/mockextensions/app.py
+++ b/tests/extension/mockextensions/app.py
@@ -4,6 +4,7 @@
 
 from jupyter_events import EventLogger
 from jupyter_events.schema_registry import SchemaRegistryException
+from tornado import web
 from traitlets import List, Unicode
 
 from jupyter_server.base.handlers import JupyterHandler
@@ -14,7 +15,7 @@
 
 EVENT_SCHEMA = """\
 $id: https://events.jupyter.org/mockapp/v1/test
-version: 1
+version: '1'
 properties:
   msg:
     type: string
@@ -44,6 +45,11 @@ def get(self):
         self.write(self.render_template("index.html"))
 
 
+class MockExtensionErrorHandler(ExtensionHandlerMixin, JupyterHandler):
+    def get(self):
+        raise web.HTTPError(418)
+
+
 class MockExtensionApp(ExtensionAppJinjaMixin, ExtensionApp):
     name = "mockextension"
     template_paths: List[str] = List().tag(config=True)  # type:ignore[assignment]
@@ -51,7 +57,12 @@ class MockExtensionApp(ExtensionAppJinjaMixin, ExtensionApp):
     mock_trait = Unicode("mock trait", config=True)
     loaded = False
 
-    serverapp_config = {"jpserver_extensions": {"tests.extension.mockextensions.mock1": True}}
+    serverapp_config = {
+        "jpserver_extensions": {
+            "tests.extension.mockextensions.mock1": True,
+            "tests.extension.mockextensions.app.mockextension_notemplate": True,
+        }
+    }
 
     @staticmethod
     def get_extension_package():
@@ -69,6 +80,20 @@ def initialize_settings(self):
     def initialize_handlers(self):
         self.handlers.append(("/mock", MockExtensionHandler))
         self.handlers.append(("/mock_template", MockExtensionTemplateHandler))
+        self.handlers.append(("/mock_error_template", MockExtensionErrorHandler))
+        self.loaded = True
+
+
+class MockExtensionNoTemplateApp(ExtensionApp):
+    name = "mockextension_notemplate"
+    loaded = False
+
+    @staticmethod
+    def get_extension_package():
+        return "tests.extension.mockextensions"
+
+    def initialize_handlers(self):
+        self.handlers.append(("/mock_error_notemplate", MockExtensionErrorHandler))
         self.loaded = True
 
 
diff --git a/tests/extension/test_app.py b/tests/extension/test_app.py
index d1add54344..ae324756ec 100644
--- a/tests/extension/test_app.py
+++ b/tests/extension/test_app.py
@@ -32,6 +32,7 @@ def mock_extension(extension_manager):
     pkg = extension_manager.extensions[name]
     point = pkg.extension_points["mockextension"]
     app = point.app
+    app.initialize()
     return app
 
 
@@ -170,12 +171,14 @@ async def _stop(*args):
         "Shutting down 2 extensions",
         "jupyter_server_terminals | extension app 'jupyter_server_terminals' stopping",
         f"{extension_name} | extension app 'mockextension' stopping",
+        f"{extension_name} | extension app 'mockextension_notemplate' stopping",
         "jupyter_server_terminals | extension app 'jupyter_server_terminals' stopped",
         f"{extension_name} | extension app 'mockextension' stopped",
+        f"{extension_name} | extension app 'mockextension_notemplate' stopped",
     }
 
     # check the shutdown method was called twice
-    assert calls == 2
+    assert calls == 3
 
 
 async def test_events(jp_serverapp, jp_fetch):
diff --git a/tests/extension/test_handler.py b/tests/extension/test_handler.py
index af4d0568ec..050f734eb4 100644
--- a/tests/extension/test_handler.py
+++ b/tests/extension/test_handler.py
@@ -1,4 +1,7 @@
+from html.parser import HTMLParser
+
 import pytest
+from tornado.httpclient import HTTPClientError
 
 
 @pytest.fixture
@@ -118,3 +121,69 @@ async def test_base_url(jp_fetch, jp_server_config, jp_base_url):
     assert r.code == 200
     body = r.body.decode()
     assert "mock static content" in body
+
+
+class StylesheetFinder(HTMLParser):
+    """Minimal HTML parser to find iframe.src attr"""
+
+    def __init__(self):
+        super().__init__()
+        self.stylesheets = []
+        self.body_chunks = []
+        self.in_head = False
+        self.in_body = False
+        self.in_script = False
+
+    def handle_starttag(self, tag, attrs):
+        tag = tag.lower()
+        if tag == "head":
+            self.in_head = True
+        elif tag == "body":
+            self.in_body = True
+        elif tag == "script":
+            self.in_script = True
+        elif self.in_head and tag.lower() == "link":
+            attr_dict = dict(attrs)
+            if attr_dict.get("rel", "").lower() == "stylesheet":
+                self.stylesheets.append(attr_dict["href"])
+
+    def handle_endtag(self, tag):
+        if tag == "head":
+            self.in_head = False
+        if tag == "body":
+            self.in_body = False
+        if tag == "script":
+            self.in_script = False
+
+    def handle_data(self, data):
+        if self.in_body and not self.in_script:
+            data = data.strip()
+            if data:
+                self.body_chunks.append(data)
+
+
+def find_stylesheets_body(html):
+    """Find the href= attr of stylesheets
+
+    and body text of an HTML document
+
+    stylesheets are used to test static_url prefix
+    """
+    finder = StylesheetFinder()
+    finder.feed(html)
+    return (finder.stylesheets, "\n".join(finder.body_chunks))
+
+
+@pytest.mark.parametrize("error_url", ["mock_error_template", "mock_error_notemplate"])
+async def test_error_render(jp_fetch, jp_serverapp, jp_base_url, error_url):
+    with pytest.raises(HTTPClientError) as e:
+        await jp_fetch(error_url, method="GET")
+    r = e.value.response
+    assert r.code == 418
+    assert r.headers["Content-Type"] == "text/html"
+    html = r.body.decode("utf8")
+    stylesheets, body = find_stylesheets_body(html)
+    static_prefix = f"{jp_base_url}static/"
+    assert stylesheets
+    assert all(stylesheet.startswith(static_prefix) for stylesheet in stylesheets)
+    assert str(r.code) in body
diff --git a/tests/services/api/test_api.py b/tests/services/api/test_api.py
index 900280f67d..8339f6e4af 100644
--- a/tests/services/api/test_api.py
+++ b/tests/services/api/test_api.py
@@ -1,5 +1,5 @@
 import json
-from typing import Awaitable, Dict, List
+from collections.abc import Awaitable
 from unittest import mock
 
 import pytest
@@ -31,7 +31,7 @@ async def test_get_status(jp_fetch):
 
 
 class MockUser(User):
-    permissions: Dict[str, List[str]]
+    permissions: dict[str, list[str]]
 
 
 class MockIdentityProvider(IdentityProvider):
diff --git a/tests/services/contents/test_manager.py b/tests/services/contents/test_manager.py
index be79011be8..5c3e2eca50 100644
--- a/tests/services/contents/test_manager.py
+++ b/tests/services/contents/test_manager.py
@@ -3,7 +3,7 @@
 import sys
 import time
 from itertools import combinations
-from typing import Dict, Optional, Tuple
+from typing import Optional
 from unittest.mock import patch
 
 import pytest
@@ -112,7 +112,7 @@ def add_invalid_cell(notebook):
 
 async def prepare_notebook(
     jp_contents_manager: FileContentsManager, make_invalid: Optional[bool] = False
-) -> Tuple[Dict, str]:
+) -> tuple[dict, str]:
     cm = jp_contents_manager
     model = await ensure_async(cm.new_untitled(type="notebook"))
     name = model["name"]
@@ -983,9 +983,10 @@ async def test_nb_validation(jp_contents_manager):
     # successful methods and ensure that calls to the aliased "validate_nb" are
     # zero.  Note that since patching side-effects the validation error case, we'll
     # skip call-count assertions for that portion of the test.
-    with patch("nbformat.validate") as mock_validate, patch(
-        "jupyter_server.services.contents.manager.validate_nb"
-    ) as mock_validate_nb:
+    with (
+        patch("nbformat.validate") as mock_validate,
+        patch("jupyter_server.services.contents.manager.validate_nb") as mock_validate_nb,
+    ):
         # Valid notebook, save, then get
         model = await ensure_async(cm.save(model, path))
         assert "message" not in model
diff --git a/tests/services/events/mock_event.yaml b/tests/services/events/mock_event.yaml
index dabaa23db5..bf73915fb0 100644
--- a/tests/services/events/mock_event.yaml
+++ b/tests/services/events/mock_event.yaml
@@ -1,5 +1,5 @@
 $id: http://event.mock.jupyter.org/message
-version: 1
+version: "1"
 title: Message
 description: |
   Emit a message
diff --git a/tests/services/events/mockextension/mock_extension_event.yaml b/tests/services/events/mockextension/mock_extension_event.yaml
index b7c03d1a48..7354d6a094 100644
--- a/tests/services/events/mockextension/mock_extension_event.yaml
+++ b/tests/services/events/mockextension/mock_extension_event.yaml
@@ -1,5 +1,5 @@
 $id: http://event.mockextension.jupyter.org/message
-version: 1
+version: "1"
 title: Message
 description: |
   Emit a message
diff --git a/tests/services/events/test_api.py b/tests/services/events/test_api.py
index 5311f0860b..40ad8b137b 100644
--- a/tests/services/events/test_api.py
+++ b/tests/services/events/test_api.py
@@ -45,7 +45,7 @@ async def test_subscribe_websocket(event_logger, jp_ws_fetch):
 payload_1 = """\
 {
     "schema_id": "http://event.mock.jupyter.org/message",
-    "version": 1,
+    "version": "1",
     "data": {
         "event_message": "Hello, world!"
     },
@@ -56,7 +56,7 @@ async def test_subscribe_websocket(event_logger, jp_ws_fetch):
 payload_2 = """\
 {
     "schema_id": "http://event.mock.jupyter.org/message",
-    "version": 1,
+    "version": "1",
     "data": {
         "event_message": "Hello, world!"
     }
@@ -92,7 +92,7 @@ async def test_post_event(jp_fetch, event_logger_sink, payload):
 
 payload_4 = """\
 {
-    "version": 1,
+    "version": "1",
     "data": {
         "event_message": "Hello, world!"
     }
@@ -102,14 +102,14 @@ async def test_post_event(jp_fetch, event_logger_sink, payload):
 payload_5 = """\
 {
     "schema_id": "http://event.mock.jupyter.org/message",
-    "version": 1
+    "version": "1"
 }
 """
 
 payload_6 = """\
 {
     "schema_id": "event.mock.jupyter.org/message",
-    "version": 1,
+    "version": "1",
     "data": {
         "event_message": "Hello, world!"
     },
@@ -117,39 +117,43 @@ async def test_post_event(jp_fetch, event_logger_sink, payload):
 }
 """
 
-
-@pytest.mark.parametrize("payload", [payload_3, payload_4, payload_5, payload_6])
-async def test_post_event_400(jp_fetch, event_logger, payload):
-    with pytest.raises(tornado.httpclient.HTTPClientError) as e:
-        await jp_fetch("api", "events", method="POST", body=payload)
-
-    assert expected_http_error(e, 400)
-
-
 payload_7 = """\
+{
+    "schema_id": "http://event.mock.jupyter.org/UNREGISTERED-SCHEMA",
+    "version": "1",
+    "data": {
+        "event_message": "Hello, world!"
+    }
+}
+"""
+
+payload_8 = """\
 {
     "schema_id": "http://event.mock.jupyter.org/message",
-    "version": 1,
+    "version": "1",
     "data": {
         "message": "Hello, world!"
     }
 }
 """
 
-payload_8 = """\
+payload_9 = """\
 {
     "schema_id": "http://event.mock.jupyter.org/message",
     "version": 2,
     "data": {
-        "message": "Hello, world!"
+        "event_message": "Hello, world!"
     }
 }
 """
 
 
-@pytest.mark.parametrize("payload", [payload_7, payload_8])
-async def test_post_event_500(jp_fetch, event_logger, payload):
+@pytest.mark.parametrize(
+    "payload",
+    [payload_3, payload_4, payload_5, payload_6, payload_7, payload_8, payload_9],
+)
+async def test_post_event_400(jp_fetch, event_logger, payload):
     with pytest.raises(tornado.httpclient.HTTPClientError) as e:
         await jp_fetch("api", "events", method="POST", body=payload)
 
-    assert expected_http_error(e, 500)
+    assert expected_http_error(e, 400)
diff --git a/tests/test_gateway.py b/tests/test_gateway.py
index 569268d833..00aa64f111 100644
--- a/tests/test_gateway.py
+++ b/tests/test_gateway.py
@@ -10,7 +10,7 @@
 from http.cookies import SimpleCookie
 from io import BytesIO
 from queue import Empty
-from typing import Any, Dict, Union
+from typing import Any, Union
 from unittest.mock import MagicMock, patch
 
 import pytest
@@ -74,7 +74,7 @@ def generate_kernelspec(name):
 #
 # This is used to simulate inconsistency in list results from the Gateway server
 # due to issues like race conditions, bugs, etc.
-omitted_kernels: Dict[str, bool] = {}
+omitted_kernels: dict[str, bool] = {}
 
 
 def generate_model(name):
diff --git a/tests/test_serverapp.py b/tests/test_serverapp.py
index 91fa33230c..f836d1b2f8 100644
--- a/tests/test_serverapp.py
+++ b/tests/test_serverapp.py
@@ -154,8 +154,9 @@ async def test_generate_config(tmp_path, jp_configurable_serverapp):
 
 def test_server_password(tmp_path, jp_configurable_serverapp):
     password = "secret"
-    with patch.dict("os.environ", {"JUPYTER_CONFIG_DIR": str(tmp_path)}), patch.object(
-        getpass, "getpass", return_value=password
+    with (
+        patch.dict("os.environ", {"JUPYTER_CONFIG_DIR": str(tmp_path)}),
+        patch.object(getpass, "getpass", return_value=password),
     ):
         app = JupyterPasswordApp(log_level=logging.ERROR)
         app.initialize([])