diff --git a/dvc/repo/__init__.py b/dvc/repo/__init__.py
index b6b6f12d3..363ade993 100644
--- a/dvc/repo/__init__.py
+++ b/dvc/repo/__init__.py
@@ -167,7 +167,7 @@ class Repo:
         self._config = config
         self._remote = remote
         self._remote_config = remote_config
-        self._data_index = None
+        self._data_index: Optional[DataIndex] = None
         self._wait_for_lock = _wait_for_lock
 
         if rev and not fs:
diff --git a/dvc/testing/path_info.py b/dvc/testing/path_info.py
index ff0ab4dd8..0e125c873 100644
--- a/dvc/testing/path_info.py
+++ b/dvc/testing/path_info.py
@@ -265,7 +265,7 @@ class CloudURLInfo(URLInfo):
 
 
 class HTTPURLInfo(URLInfo):
-    __hash__: Callable[["HTTPURLInfo"], int] = URLInfo.__hash__
+    __hash__: Callable[["HTTPURLInfo"], int] = URLInfo.__hash__  # type: ignore[assignment]
 
     def __init__(self, url):
         p = urlparse(url)
diff --git a/dvc/utils/hydra.py b/dvc/utils/hydra.py
index 09ade0822..d9ce0bf49 100644
--- a/dvc/utils/hydra.py
+++ b/dvc/utils/hydra.py
@@ -115,6 +115,7 @@ def apply_overrides(path: "StrPath", overrides: list[str]) -> None:
         except hydra_errors as e:
             raise InvalidArgumentError("Invalid `--set-param` value") from e
 
+        assert isinstance(new_data, dict)
         merge_dicts(original_data, new_data)
         remove_missing_keys(original_data, new_data)
 
diff --git a/pyproject.toml b/pyproject.toml
index d88ac7517..2cb5898bb 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -85,7 +85,7 @@ gdrive = ["dvc-gdrive>=3,<4"]
 gs = ["dvc-gs>=3.0.2,<4"]
 hdfs = ["dvc-hdfs>=3,<4"]
 lint = [
-    "mypy==1.15.0",
+    "mypy==1.16.1",
     "pandas-stubs",
     "types-colorama",
     "types-psutil",