diff --git a/src/huggingface_hub/dataclasses.py b/src/huggingface_hub/dataclasses.py
index ed08f246f5..677cb91484 100644
--- a/src/huggingface_hub/dataclasses.py
+++ b/src/huggingface_hub/dataclasses.py
@@ -166,13 +166,27 @@ def __init__(self, **kwargs: Any) -> None:
                 # Call the original __init__ with standard fields
                 original_init(self, **standard_kwargs)
 
-                # Add any additional kwargs as attributes
+                # Pass any additional kwargs to `__post_init__` and let the object
+                # decide whether to set the attr or use for different purposes (e.g. BC checks)
+                additional_kwargs = {}
                 for name, value in kwargs.items():
                     if name not in dataclass_fields:
-                        self.__setattr__(name, value)
+                        additional_kwargs[name] = value
+
+                self.__post_init__(**additional_kwargs)
 
             cls.__init__ = __init__  # type: ignore[method-assign]
 
+            # Define a default __post_init__ if not defined
+            if not hasattr(cls, "__post_init__"):
+
+                def __post_init__(self, **kwargs: Any) -> None:
+                    """Default __post_init__ to accept additional kwargs."""
+                    for name, value in kwargs.items():
+                        setattr(self, name, value)
+
+                cls.__post_init__ = __post_init__  # type: ignore[method-assign]
+
             # (optional) Override __repr__ to include additional kwargs
             original_repr = cls.__repr__
 
diff --git a/tests/test_utils_strict_dataclass.py b/tests/test_utils_strict_dataclass.py
index 2b1b147b23..fb8cf1094b 100644
--- a/tests/test_utils_strict_dataclass.py
+++ b/tests/test_utils_strict_dataclass.py
@@ -84,6 +84,18 @@ class ConfigWithKwargs:
     vocab_size: int = validated_field(validator=positive_int, default=16)
 
 
+@strict(accept_kwargs=True)
+@dataclass
+class ConfigWithKwargsAndPostInit:
+    model_type: str
+    vocab_size: int = validated_field(validator=positive_int, default=16)
+
+    def __post_init__(self, **kwargs: Any) -> None:
+        """Custom __post_init__ that also accepts additional kwargs."""
+        for name, value in kwargs.items():
+            setattr(self, name.upper(), value)  # store additional kwargs in uppercase (just for testing)
+
+
 class DummyClass:
     pass
 
@@ -376,6 +388,13 @@ class Config:
         Config(model_type="bert", vocab_size=30000)
 
 
+def test_post_init_with_kwargs():
+    config = ConfigWithKwargsAndPostInit(model_type="bert", vocab_size=30000, extra_param="extra_value")
+    assert config.model_type == "bert"
+    assert config.vocab_size == 30000
+    assert config.EXTRA_PARAM == "extra_value"  # stored in uppercase by custom __post_init__
+
+
 def test_is_recognized_as_dataclass():
     # Check that dataclasses module recognizes it as a dataclass
     assert is_dataclass(Config)