diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index cca23aa4b..1a116b30b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -140,6 +140,18 @@ jobs:
           key: poetry-${{ hashFiles('poetry.lock') }}
           restore-keys: poetry-
 
+      # Mypy is incremental: with a restored .mypy_cache it only re-checks
+      # modules whose dependencies changed. The key includes the commit SHA so
+      # every run saves a fresh snapshot (actions/cache never overwrites an
+      # existing key); restore-keys falls back to the most recent snapshot for
+      # the same deps/config.
+      - name: Cache mypy incremental state
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9
+        with:
+          path: .mypy_cache
+          key: mypy-${{ hashFiles('poetry.lock', 'pyproject.toml') }}-${{ github.sha }}
+          restore-keys: mypy-${{ hashFiles('poetry.lock', 'pyproject.toml') }}-
+
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip