diff --git a/stac_fastapi/api/stac_fastapi/api/models.py b/stac_fastapi/api/stac_fastapi/api/models.py
index 1c2146d..4fb3c50 100644
--- a/stac_fastapi/api/stac_fastapi/api/models.py
+++ b/stac_fastapi/api/stac_fastapi/api/models.py
@@ -47,7 +47,30 @@ def create_request_model(
 
     # Handle GET requests
     if all([issubclass(m, APIRequest) for m in models]):
-        return make_dataclass(model_name, [], bases=tuple(models))
+        # Collect fields from all parent models to avoid __post_init__ conflicts
+        for model in models:
+            if hasattr(model, '__dataclass_fields__'):
+                for k, field_info in model.__dataclass_fields__.items():
+                    if k not in fields:  # Avoid duplicates, parents take precedence
+                        fields[k] = (field_info.type, field_info.default)
+            elif hasattr(model, 'model_fields'):
+                for k, field_info in model.model_fields.items():
+                    if k not in fields:  # Avoid duplicates
+                        fields[k] = (field_info.annotation, field_info.default)
+        
+        # Create the dataclass with collected fields
+        Dataclass = make_dataclass(model_name, list(fields.items()), bases=tuple(models))
+        
+        # Add a __post_init__ method that properly chains to parent __post_init__ methods
+        def _post_init__(self):
+            """Chain to all parent __post_init__ methods."""
+            # Call __post_init__ on each parent class in MRO order (excluding self and object)
+            for cls in type(self).__mro__[1:-1]:  # Skip self (index 0) and object (last)
+                if hasattr(cls, '__post_init__'):
+                    cls.__post_init__(self)
+        
+        Dataclass.__post_init__ = _post_init__
+        return Dataclass
 
     # Handle POST requests
     elif all([issubclass(m, BaseModel) for m in models]):
@@ -134,4 +157,4 @@ class GeoJSONResponse(JSONResponse):
 class JSONSchemaResponse(JSONResponse):
     """JSON with custom, vendor content-type."""
 
-    media_type = "application/schema+json"
+    media_type = "application/schema+json"
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