diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index bc6938e..bddfd77 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -9,7 +9,7 @@ jobs:
     strategy:
       matrix:
         os: [macos-latest, windows-latest, ubuntu-latest]
-        python-version: ['3.10', '3.11', '3.12', '3.13', '3.14', pypy-3.11]
+        python-version: ['3.11', '3.12', '3.13', '3.14', '3.15', pypy-3.11]
     steps:
       - uses: actions/checkout@v7.0.1
       - uses: actions/setup-python@v7.1.0
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 619f4bc..4c885b0 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -7,12 +7,12 @@ Unreleased
 Added
 ~~~~~
 
--  Add support for Python 3.13, 3.14.
+-  Add support for Python 3.13, 3.14, 3.15.
 
 Removed
 ~~~~~~~
 
--  Drop support for Python 3.9.
+-  Drop support for Python 3.9, 3.10.
 
 0.0.4 (2024-09-15)
 ------------------
diff --git a/oc4idskit/transforms.py b/oc4idskit/transforms.py
index 606050f..2630ded 100644
--- a/oc4idskit/transforms.py
+++ b/oc4idskit/transforms.py
@@ -433,7 +433,7 @@ def administrative_entity(state):
 
 def contract_status(state):
     """CoST IDS element: Contract status."""
-    current_iso_datetime = dt.datetime.now(tz=dt.timezone.utc).isoformat()
+    current_iso_datetime = dt.datetime.now(tz=dt.UTC).isoformat()
 
     for compiled_release, contracting_process in zip(
         state.compiled_releases, state.output["contractingProcesses"], strict=True
diff --git a/pyproject.toml b/pyproject.toml
index 202019f..4a240fc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,15 +13,15 @@ urls = {Homepage = "https://github.com/open-contracting/oc4idskit"}
 classifiers = [
     "License :: OSI Approved :: BSD License",
     "Operating System :: OS Independent",
-    "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
     "Programming Language :: Python :: 3.14",
+    "Programming Language :: Python :: 3.15",
     "Programming Language :: Python :: Implementation :: CPython",
     "Programming Language :: Python :: Implementation :: PyPy",
 ]
-requires-python = ">=3.10"
+requires-python = ">=3.11"
 dependencies = [
     "jsonpointer",
     "ocdskit>=1.1.2",