diff --git a/llmrelic/registry.py b/llmrelic/registry.py
index a0bb12b..1eb8d2a 100644
--- a/llmrelic/registry.py
+++ b/llmrelic/registry.py
@@ -54,15 +54,21 @@ def get_supported_models(self) -> List[str]:
         return sorted(self._supported_models)
 
     def get_supported_by_provider(self) -> Dict[str, List[str]]:
-        """Get supported models organized by provider."""
-        result = {}
+        """
+        Get supported models organized by provider.
+        A slightly optimized version is used to set intersections instead of calling ``is_supported`` for every model in the provider. This reduces Python overhead when the registry contains many models and providers have large model lists.
+        """
+        result: Dict[str, List[str]] = {}
+        # local reference to avoid global lookups in loop
+        supported = self._supported_models
         for provider_name, provider in PROVIDERS.items():
-            supported = [
-                model for model in provider.list_models()
-                if self.is_supported(model)
-            ]
-            if supported:
-                result[provider_name] = supported
+            # intersect the two sets; provider.list_models() returns a list so
+            # convert to set once
+            provider_models = set(provider.list_models())
+            matches = supported & provider_models
+            if matches:
+                # sort for deterministic output (tests rely on some ordering)
+                result[provider_name] = sorted(matches)
         return result
 
     def clear(self) -> "ModelRegistry":
diff --git a/tests/test_registry.py b/tests/test_registry.py
index 2675a21..510b64b 100644
--- a/tests/test_registry.py
+++ b/tests/test_registry.py
@@ -153,6 +153,21 @@ def test_get_supported_by_provider_excludes_empty_providers(self):
         assert "cohere" not in result
         assert "mistral" not in result
 
+    def test_get_supported_by_provider_output_is_sorted(self):
+        """The list returned for each provider should be sorted alphabetically.
+
+        This test also indirectly verifies that our optimized intersection logic
+        doesn't break existing functionality when models are added in an
+        arbitrary order.
+        """
+        registry = ModelRegistry()
+        # insert models in reverse order intentionally
+        for model in reversed(OpenAI.list_models()):
+            registry.add_model(model)
+        result = registry.get_supported_by_provider()
+        openai_models = result.get("openai", [])
+        assert openai_models == sorted(openai_models)
+
     def test_clear(self):
         """clear() should remove all models."""
         registry = ModelRegistry()