refactor: move native OpenRouter check to get_llm_provider before strip

The previous check in _get_openai_compatible_provider_info() ran after
the model name was already split, so it never caught the second
get_llm_provider() call from the anthropic_messages bridge.

Moved the check to get_llm_provider() before the provider-list
stripping, using a pattern-based approach (custom_llm_provider ==
"openrouter" and model.startswith("openrouter/")) instead of a
hardcoded set. This covers all current and future native OpenRouter
models.

Updated tests to verify the bridge double-call scenario with
custom_llm_provider passed through.

litellm/litellm_core_utils/get_llm_provider_logic.py

@@ -158,6 +158,14 @@ def get_llm_provider(  # noqa: PLR0915
         ):  # handle scenario where model="azure/*" and custom_llm_provider="azure"
             model = custom_llm_provider + "/" + model
 
+        # Native OpenRouter models have IDs like "openrouter/free" where the
+        # "openrouter/" prefix is part of the actual model name on the API.
+        # When called from a bridge (e.g. anthropic_messages adapter),
+        # custom_llm_provider is already resolved, so return early to prevent
+        # the provider-list stripping below from removing the prefix.
+        if custom_llm_provider == "openrouter" and model.startswith("openrouter/"):
+            return model, custom_llm_provider, dynamic_api_key, api_base
+
         if api_key and api_key.startswith("os.environ/"):
             dynamic_api_key = get_secret_str(api_key)
 
@@ -504,15 +512,6 @@ def _get_openai_compatible_provider_info(  # noqa: PLR0915
     custom_llm_provider = model.split("/", 1)[0]
     model = model.split("/", 1)[1]
 
-    # If the provider is openrouter and the remaining model name still starts
-    # with "openrouter/", that inner prefix is part of the actual model ID on
-    # the OpenRouter API (e.g. openrouter/openrouter/aurora-alpha →
-    # model="openrouter/aurora-alpha").  Return immediately so the prefix is
-    # not stripped a second time.
-    if custom_llm_provider == "openrouter" and model.startswith("openrouter/"):
-        dynamic_api_key = api_key or get_secret_str("OPENROUTER_API_KEY")
-        return model, custom_llm_provider, dynamic_api_key, api_base
-
     # Check JSON providers FIRST (before hardcoded ones)
     from litellm.llms.openai_like.dynamic_config import create_config_class
     from litellm.llms.openai_like.json_loader import JSONProviderRegistry

tests/test_litellm/llms/openrouter/test_openrouter_provider_routing.py

@@ -44,31 +44,37 @@ class TestOpenRouterNativeModelRouting:
         assert result_model == expected_model
 
     @pytest.mark.parametrize(
-        "input_model,expected_first,expected_second",
+        "input_model",
         [
-            # After the first call strips outer prefix: openrouter/openrouter/aurora-alpha
-            # → openrouter/aurora-alpha.  A second call on that result splits at the
-            # first "/" giving provider=openrouter, model=aurora-alpha — which is the
-            # correct model ID to send to the OpenRouter API.
-            ("openrouter/openrouter/aurora-alpha", "openrouter/aurora-alpha", "aurora-alpha"),
-            ("openrouter/openrouter/auto", "openrouter/auto", "auto"),
+            "openrouter/openrouter/aurora-alpha",
+            "openrouter/openrouter/auto",
+            "openrouter/openrouter/free",
+            "openrouter/openrouter/some-future-model",
         ],
     )
-    def test_no_double_strip_on_second_call(self, input_model, expected_first, expected_second):
+    def test_bridge_double_call_preserves_native_model(self, input_model):
         """Simulates two consecutive get_llm_provider calls (bridge → completion).
 
-        The first call (bridge) converts openrouter/openrouter/<model> to
-        openrouter/<model>.  The second call (completion) further strips the
-        remaining openrouter/ provider prefix and returns <model> — the bare
-        model ID that should be sent to the OpenRouter API.
+        The first call (bridge) strips the outer prefix:
+            openrouter/openrouter/<model> → openrouter/<model>
+
+        The second call (completion) receives custom_llm_provider="openrouter"
+        from the bridge, detects the native model, and preserves it:
+            openrouter/<model> → openrouter/<model>  (no further stripping)
         """
+        # First call: bridge resolves provider
         model_first, provider, _, _ = litellm.get_llm_provider(model=input_model)
         assert provider == "openrouter"
-        assert model_first == expected_first
+        expected_model = input_model.split("/", 1)[1]  # openrouter/<model>
+        assert model_first == expected_model
 
-        model_second, provider2, _, _ = litellm.get_llm_provider(model=model_first)
+        # Second call: completion receives model + custom_llm_provider from bridge
+        model_second, provider2, _, _ = litellm.get_llm_provider(
+            model=model_first,
+            custom_llm_provider="openrouter",
+        )
         assert provider2 == "openrouter"
-        assert model_second == expected_second
+        assert model_second == expected_model  # preserved, not stripped further
 
     @pytest.mark.parametrize(
         "input_model,expected_model",