@@ -288,12 +288,12 @@ def per_page(self) -> int:
         return self._list.per_page
 
     @property
-    def total_pages(self) -> int:
+    def total_pages(self) -> Optional[int]:
         """The total number of pages."""
         return self._list.total_pages
 
     @property
-    def total(self) -> int:
+    def total(self) -> Optional[int]:
         """The total number of items."""
         return self._list.total
 
 
@@ -966,17 +966,25 @@ def per_page(self) -> int:
         return int(self._per_page)
 
     @property
-    def total_pages(self) -> int:
+    def total_pages(self) -> Optional[int]:
         """The total number of pages."""
-        if TYPE_CHECKING:
-            assert self._total_pages is not None
+        if self._total_pages is None:
+            # NOTE(jlvillal): When more than 10,000 items are returned on
+            # https://gitlab.com/ then the header for this value will not be
+            # returned. So we return None.
+            # https://docs.gitlab.com/ee/user/gitlab_com/index.html#pagination-response-headers
+            return None
         return int(self._total_pages)
 
     @property
-    def total(self) -> int:
+    def total(self) -> Optional[int]:
         """The total number of items."""
-        if TYPE_CHECKING:
-            assert self._total is not None
+        if self._total is None:
+            # NOTE(jlvillal): When more than 10,000 items are returned on
+            # https://gitlab.com/ then the header for this value will not be
+            # returned. So we return None.
+            # https://docs.gitlab.com/ee/user/gitlab_com/index.html#pagination-response-headers
+            return None
         return int(self._total)
 
     def __iter__(self) -> "GitlabList":