diff --git a/spacy/schemas.py b/spacy/schemas.py
index 658eeb574..555a505d7 100644
--- a/spacy/schemas.py
+++ b/spacy/schemas.py
@@ -11,6 +11,7 @@ import inspect
 
 from .attrs import NAMES
 from .lookups import Lookups
+from .util import is_cython_func
 
 if TYPE_CHECKING:
     # This lets us add type hints for mypy etc. without causing circular imports
@@ -93,8 +94,11 @@ def get_arg_model(
             continue
         # If no annotation is specified assume it's anything
         annotation = param.annotation if param.annotation != param.empty else Any
-        # If no default value is specified assume that it's required
-        default = param.default if param.default != param.empty else ...
+        # If no default value is specified assume that it's required. Cython
+        # functions/methods will have param.empty for default value None so we
+        # need to treat them differently
+        default_empty = None if is_cython_func(func) else ...
+        default = param.default if param.default != param.empty else default_empty
         sig_args[param.name] = (annotation, default)
     is_strict = strict and not has_variable
     sig_args["__config__"] = ArgSchemaConfig if is_strict else ArgSchemaConfigExtra
diff --git a/spacy/util.py b/spacy/util.py
index 1e0a8e7d4..98c2a4083 100644
--- a/spacy/util.py
+++ b/spacy/util.py
@@ -1310,3 +1310,21 @@ def minibatch(items, size):
         if len(batch) == 0:
             break
         yield list(batch)
+
+
+def is_cython_func(func: Callable) -> bool:
+    """Slightly hacky check for whether a callable is implemented in Cython.
+    Can be used to implement slightly different behaviors, especially around
+    inspecting and parameter annotations.
+
+    func (Callable): The callable to check.
+    RETURNS (bool): Whether the callable is Cython (probably).
+    """
+    attr = "__reduce_cython__"
+    if hasattr(func, attr):  # function or class instance
+        return True
+    # https://stackoverflow.com/a/55767059
+    if hasattr(func, "__qualname__") and hasattr(func, "__module__"):  # method
+        cls_func = vars(sys.modules[func.__module__])[func.__qualname__.split(".")[0]]
+        return hasattr(cls_func, attr)
+    return False