diff --git a/.circleci/config.yml b/.circleci/config.yml
index f3be267d..394e6f2d 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -44,12 +44,12 @@ jobs:
   # Python jobs, so it costs a venv restore and one test file.
   api-contract-tests:
     docker:
-      - image: cimg/python:3.11
+      - image: cimg/python:3.13
     resource_class: medium
     steps:
       - checkout
       - restore_cache:
-          key: deps-3.11-{{ checksum "requirements.txt" }}-5
+          key: deps-3.13-{{ checksum "requirements.txt" }}-5
       - run:
           name: Install Requirements
           command: |
diff --git a/.github/workflows/controller-tests.yml b/.github/workflows/controller-tests.yml
index a1c005ad..21739c62 100644
--- a/.github/workflows/controller-tests.yml
+++ b/.github/workflows/controller-tests.yml
@@ -21,6 +21,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v5
         with:
+          # Trixie ships 3.13, and docker/controller/Dockerfile is python:3.13-slim-trixie.
           python-version: '3.13'
           cache: 'pip'
           cache-dependency-path: controller/requirements.txt