diff --git a/src/monty/collections.py b/src/monty/collections.py
index b9d463f7..0a6f242a 100644
--- a/src/monty/collections.py
+++ b/src/monty/collections.py
@@ -6,7 +6,7 @@
 
 import collections
 from abc import ABC, abstractmethod
-from typing import TYPE_CHECKING, Mapping
+from typing import TYPE_CHECKING, Mapping, overload
 
 if TYPE_CHECKING:
     from typing import Any, Iterable
@@ -204,15 +204,24 @@ def __contains__(self, key: Any) -> bool:
         """Checks if a case-insensitive key is `in` the dictionary."""
         return super().__contains__(self._converter(key))
 
-    def __ior__(self, other: Mapping) -> Self:
-        """The |= operator."""
+    def __ior__(self, other: Mapping | Iterable, /) -> Self:
+        """The `|=` operator."""
         self.update(other)
         return self
 
+    def __or__(self, other: Mapping[Any, Any]) -> Self:
+        """The `|` operator."""
+        if not isinstance(other, Mapping):
+            return NotImplemented
+
+        new_dict = type(self)(self)
+        new_dict.update(other)
+        return new_dict
+
     def setdefault(self, key: Any, default: Any = None) -> Any:
         return super().setdefault(self._converter(key), default)
 
-    def update(self, *args: Iterable[Mapping], **kwargs: Any) -> None:
+    def update(self, *args, **kwargs: Any) -> None:
         if args:
             for mapping in args:
                 if isinstance(mapping, Mapping):
diff --git a/tests/test_collections.py b/tests/test_collections.py
index 504a4262..f98076cc 100644
--- a/tests/test_collections.py
+++ b/tests/test_collections.py
@@ -140,6 +140,29 @@ def test_ior_operator(self):
         assert self.upper_dict["F"] == 8
         assert self.upper_dict["f"] == 8
 
+    def test_or_operator(self):
+        # Test with another CaseInsensitiveDictUpper
+        other = CaseInsensitiveDictUpper({"E": 7, "F": 8})
+        result = self.upper_dict | other
+        assert isinstance(result, CaseInsensitiveDictUpper)
+        assert result["E"] == 7
+        assert result["e"] == 7
+        assert result["F"] == 8
+        assert result["f"] == 8
+        assert result["HI"] == "world"
+        assert result["hi"] == "world"
+
+        # Test with a regular dict
+        other = {"g": 9, "H": 10}
+        result = self.upper_dict | other
+        assert isinstance(result, CaseInsensitiveDictUpper)
+        assert result["G"] == 9
+        assert result["g"] == 9
+        assert result["H"] == 10
+        assert result["h"] == 10
+        assert result["HI"] == "world"
+        assert result["hi"] == "world"
+
     def test_setdefault(self):
         assert self.upper_dict.setdefault("g", 9) == 9
         assert self.upper_dict["G"] == 9