diff --git a/.github/workflows/build-release.yml b/.github/workflows/build-release.yml
index f5cf612..638b77f 100644
--- a/.github/workflows/build-release.yml
+++ b/.github/workflows/build-release.yml
@@ -13,8 +13,10 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - { name: "3.8", python: "3.8", tox: py38 }
-          - { name: "3.12", python: "3.12", tox: py312 }
+          - { name: "3.9", python: "3.9", tox: py39-marshmallow3 }
+          - { name: "3.13", python: "3.13", tox: py313-marshmallow3 }
+          - { name: "lowest", python: "3.9", tox: py39-lowest }
+          - { name: "dev", python: "3.13", tox: py313-marshmallowdev }
     steps:
       - uses: actions/checkout@v4.0.0
       - uses: actions/setup-python@v4.7.0
@@ -34,7 +36,7 @@ jobs:
       - uses: actions/checkout@v4.0.0
       - uses: actions/setup-python@v4.7.0
         with:
-          python-version: "3.11"
+          python-version: "3.13"
       - run: python -m pip install --upgrade pip
       - run: python -m pip install tox
       - run: python -m tox -e lint
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index d129547..c8d23fc 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -14,7 +14,7 @@ repos:
   rev: 1.19.1
   hooks:
   - id: blacken-docs
-    additional_dependencies: [black==23.12.1]
+    additional_dependencies: [black==24.10.0]
 - repo: https://github.com/pre-commit/mirrors-mypy
   rev: v1.14.1
   hooks:
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index e3e65fe..c4ab889 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -1,6 +1,14 @@
 Changelog
 ---------
 
+3.2.0 (unreleased)
+******************
+
+Support:
+
+- Support Python 3.9-3.13.
+- Support marshmallow 3-4.
+
 3.1.1 (2024-02-13)
 ++++++++++++++++++
 
diff --git a/README.rst b/README.rst
index 3f5247f..bc09dfa 100644
--- a/README.rst
+++ b/README.rst
@@ -12,9 +12,9 @@ marshmallow-oneofschema
     :target: https://github.com/marshmallow-code/flask-marshmallow/actions/workflows/build-release.yml
     :alt: Build status
 
-.. |marshmallow3| image:: https://badgen.net/badge/marshmallow/3
+.. |marshmallow-support| image:: https://badgen.net/badge/marshmallow/3,4?list=1
     :target: https://marshmallow.readthedocs.io/en/latest/upgrading.html
-    :alt: marshmallow 3 compatible
+    :alt: marshmallow 3|4 compatible
 
 An extension to marshmallow to support schema (de)multiplexing.
 
diff --git a/pyproject.toml b/pyproject.toml
index f81be52..e72cb2b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,13 +10,13 @@ classifiers = [
   "Intended Audience :: Developers",
   "License :: OSI Approved :: MIT License",
   "Programming Language :: Python :: 3",
-  "Programming Language :: Python :: 3.8",
   "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: 3.12",
+  "Programming Language :: Python :: 3.13",
 ]
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 dependencies = ["marshmallow>=3.0.0,<4.0.0"]
 
 [project.urls]
@@ -53,3 +53,10 @@ select = [
   "UP", # pyupgrade
   "W",  # pycodestyle warning
 ]
+
+[tool.mypy]
+ignore_missing_imports = true
+warn_unreachable = true
+warn_unused_ignores = true
+warn_redundant_casts = true
+no_implicit_optional = true
diff --git a/src/marshmallow_oneofschema/one_of_schema.py b/src/marshmallow_oneofschema/one_of_schema.py
index 71ea765..464d55b 100644
--- a/src/marshmallow_oneofschema/one_of_schema.py
+++ b/src/marshmallow_oneofschema/one_of_schema.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import typing
 
 from marshmallow import Schema, ValidationError
@@ -59,7 +61,7 @@ def get_obj_type(self, obj):
 
     type_field = "type"
     type_field_remove = True
-    type_schemas: typing.Mapping[str, typing.Union[typing.Type[Schema], Schema]] = {}
+    type_schemas: typing.Mapping[str, type[Schema] | Schema] = {}
 
     def get_obj_type(self, obj):
         """Returns name of the schema during dump() calls, given the object
diff --git a/tox.ini b/tox.ini
index 0e74a88..2574d22 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,14 +1,20 @@
 [tox]
 envlist=
     lint
-    py{38,39,310,311,312}
+    py{39,310,311,312,313}-marshmallow3
+    py313-marshmallowdev
+    py39-lowest
 
 [testenv]
 extras = tests
+deps =
+    marshmallow3: marshmallow>=3.0.0,<4.0.0
+    marshmallowdev: https://github.com/marshmallow-code/marshmallow/archive/dev.tar.gz
+    lowest: marshmallow==3.0.0
 commands = pytest {posargs}
 
 [testenv:lint]
-deps = pre-commit~=3.5
+deps = pre-commit~=4.0.1
 skip_install = true
 commands = pre-commit run --all-files