diff --git a/.black.cfg.toml b/.black.cfg.toml
index da415726..a1c8ede5 100644
--- a/.black.cfg.toml
+++ b/.black.cfg.toml
@@ -9,4 +9,4 @@
 include = '\.pyi?$'
 line-length = 100
 skip-string-normalization = true
-target-version = ['py39', 'py310', 'py311', 'py312', 'py313', 'py314']
+target-version = ['py310', 'py311', 'py312', 'py313', 'py314']
diff --git a/.bumpversion.cfg b/.bumpversion.cfg
index 6303387d..b08c4380 100644
--- a/.bumpversion.cfg
+++ b/.bumpversion.cfg
@@ -1,5 +1,5 @@
 [bumpversion]
-current_version = 0.75.0
+current_version = 0.76.0
 commit = True
 tag = False
 message = chore: Bump version from {current_version} to {new_version}
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index eae33a1d..9fb17858 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -28,7 +28,6 @@ jobs:
     strategy:
       matrix:
         python_version:
-          - "3.9"
           - "3.10"
           - "3.11"
           - "3.12"
@@ -90,7 +89,6 @@ jobs:
     strategy:
       matrix:
         python_version:
-          - "3.9"
           - "3.10"
           - "3.11"
           - "3.12"
@@ -158,7 +156,7 @@ jobs:
 
       - name: Check that compiled Python dependency manifests are up-to-date with their sources
         # FIXME: There are issues related to testing with multiple Python versions.
-        if: ${{ startsWith(steps.set_up_python.outputs.python-version, '3.9.') }}
+        if: ${{ startsWith(steps.set_up_python.outputs.python-version, '3.10.') }}
         run: |
           source "$PYTHON_VIRTUALENV_ACTIVATE"
           make python-deps-sync-check
diff --git a/HISTORY.md b/HISTORY.md
index 4006daae..210703d4 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,5 +1,10 @@
 # History
 
+## 0.76.0 (2026-05-04)
+
+- (PR #1029, 2026-04-29) Drop support for Python 3.9
+- (PR #1028, 2026-04-30) Bump marshmallow from 4.0.1 to 4.3.0
+
 ## 0.75.0 (2026-04-15)
 
 - (PR #1024, 2026-04-15) Fix Python version and caching in CI/CD
diff --git a/README.md b/README.md
index 7046c03c..33041c20 100644
--- a/README.md
+++ b/README.md
@@ -31,8 +31,7 @@ The full documentation is at <https://lib-cl-sii-python.readthedocs.io>.
 
 ## Supported Python versions
 
-Only Python 3.9, 3.10, 3.11, 3.12, 3.13, and 3.14. Python 3.8 and below will not work because we use
-some features introduced in Python 3.9.
+Only Python 3.10, 3.11, 3.12, 3.13, and 3.14. Python 3.9 and below will not work.
 
 ## Quickstart
 
diff --git a/mypy.ini b/mypy.ini
index f3bb76a0..8f397de0 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,5 +1,5 @@
 [mypy]
-python_version = 3.9
+python_version = 3.10
 platform = linux
 mypy_path =
     src
diff --git a/pyproject.toml b/pyproject.toml
index 995ff368..9306f320 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -42,7 +42,6 @@ classifiers = [
   "Intended Audience :: Developers",
   "Natural Language :: English",
   "Programming Language :: Python :: 3",
-  "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: 3.12",
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 317f5e16..063b9d36 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,5 +1,5 @@
 #
-# This file is autogenerated by pip-compile with Python 3.9
+# This file is autogenerated by pip-compile with Python 3.10
 # by the following command:
 #
 #    pip-compile --allow-unsafe --strip-extras requirements-dev.in
@@ -67,10 +67,7 @@ idna==3.7
 importlib-metadata==8.7.0
     # via
     #   -c requirements.txt
-    #   build
-    #   isort
     #   keyring
-    #   twine
 isort==6.1.0
     # via -r requirements-dev.in
 jaraco-classes==3.4.0
@@ -171,7 +168,7 @@ six==1.16.0
     # via bleach
 soupsieve==2.6
     # via beautifulsoup4
-tomli==2.2.1
+tomli==2.4.1
     # via
     #   black
     #   build
diff --git a/requirements.in b/requirements.in
index f7ad120b..fa37817d 100644
--- a/requirements.in
+++ b/requirements.in
@@ -5,7 +5,6 @@
 # Note: To install a package from a Git VCS repository, see the following example:
 #   git+https://github.com/example/example.git@example-vcs-ref#egg=example-pkg[foo,bar]==1.42.3
 
-backports-zoneinfo==0.2.1 ; python_version < "3.9" # Used by `djangorestframework`.
 cryptography==46.0.7
 defusedxml==0.7.1
 django-filter>=24.2
@@ -14,7 +13,7 @@ djangorestframework>=3.10.3,<3.17
 importlib-metadata==8.7.0
 jsonschema==4.25.1
 lxml==6.0.2
-marshmallow==4.0.1
+marshmallow==4.3.0
 pydantic==2.12.5
 pyOpenSSL==26.0.0
 pytz==2025.2
diff --git a/requirements.txt b/requirements.txt
index 1654b247..e524e509 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
 #
-# This file is autogenerated by pip-compile with Python 3.9
+# This file is autogenerated by pip-compile with Python 3.10
 # by the following command:
 #
 #    pip-compile --allow-unsafe --strip-extras requirements.in
@@ -44,7 +44,7 @@ lxml==6.0.2
     # via
     #   -r requirements.in
     #   signxml
-marshmallow==4.0.1
+marshmallow==4.3.0
     # via -r requirements.in
 pycparser==2.22
     # via cffi
diff --git a/src/cl_sii/__init__.py b/src/cl_sii/__init__.py
index 029f6f0a..19b83fc9 100644
--- a/src/cl_sii/__init__.py
+++ b/src/cl_sii/__init__.py
@@ -4,4 +4,4 @@
 
 """
 
-__version__ = '0.75.0'
+__version__ = '0.76.0'
diff --git a/tox.ini b/tox.ini
index 412bfaf1..ff733517 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,5 @@
 [tox]
 envlist =
-    py39,
     py310,
     py311,
     py312,
@@ -15,7 +14,6 @@ deps =
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/requirements-dev.txt
 basepython =
-    py39: python3.9
     py310: python3.10
     py311: python3.11
     py312: python3.12