diff --git a/apis/python/src/tiledbsoma/io/shaping.py b/apis/python/src/tiledbsoma/io/shaping.py
index f00f81d835..2a74ecdfb0 100644
--- a/apis/python/src/tiledbsoma/io/shaping.py
+++ b/apis/python/src/tiledbsoma/io/shaping.py
@@ -18,18 +18,15 @@
 Printable = Union[io.TextIOWrapper, io.StringIO]
 
 
-class SizingArgs(TypedDict):
-    """Convenience type-alias for kwargs passed to experiment-level
-    upgrade/resize functions.
-    """
-
-    nobs: Optional[int]
-    nvars: Optional[Dict[str, int]]
-    ms_name: Optional[str]
-    coll_name: Optional[str]
-    verbose: bool
-    check_only: bool
-    context: Optional[tiledbsoma.SOMATileDBContext]
+@attr.s(auto_attribs=True, frozen=True)
+class SizingArgs:
+    nobs: Optional[int] = None
+    nvars: Optional[Dict[str, int]] = None
+    ms_name: Optional[str] = None
+    coll_name: Optional[str] = None
+    verbose: bool = True
+    check_only: bool = True
+    context: Optional[tiledbsoma.SOMATileDBContext] = None
     output_handle: Printable