diff --git a/litellm/litellm_core_utils/get_llm_provider_logic.py b/litellm/litellm_core_utils/get_llm_provider_logic.py
index 95bcd4d7186..ea8ff64477c 100644
--- a/litellm/litellm_core_utils/get_llm_provider_logic.py
+++ b/litellm/litellm_core_utils/get_llm_provider_logic.py
@@ -158,6 +158,13 @@ def get_llm_provider(  # noqa: PLR0915
         ):  # handle scenario where model="azure/*" and custom_llm_provider="azure"
             model = custom_llm_provider + "/" + model
 
+        # Resolve `os.environ/` api_key placeholders before the OpenRouter
+        # early return below, so callers passing
+        # `api_key="os.environ/OPENROUTER_API_KEY"` still get the secret
+        # resolved when the model routes via the `openrouter/` prefix.
+        if api_key and api_key.startswith("os.environ/"):
+            dynamic_api_key = get_secret_str(api_key)
+
         # OpenRouter: when the router/proxy already set custom_llm_provider,
         # the model may still carry LiteLLM's "openrouter/" routing prefix.
         # Native IDs like "openrouter/auto" must stay intact for the API; IDs
diff --git a/litellm/llms/openrouter/chat/transformation.py b/litellm/llms/openrouter/chat/transformation.py
index 86e63fd0c41..458e1576a52 100644
--- a/litellm/llms/openrouter/chat/transformation.py
+++ b/litellm/llms/openrouter/chat/transformation.py
@@ -159,6 +159,16 @@ class OpenrouterConfig(OpenAIGPTConfig):
         Returns:
             dict: The transformed request. Sent as the body of the API call.
         """
+        # Defensive strip of the "openrouter/" prefix for code paths that
+        # reach this transform without going through get_llm_provider (e.g.
+        # some adapter/bridge invocations). Native IDs like
+        # "openrouter/auto" / "openrouter/free" have no "/" after the prefix
+        # and must be kept intact.
+        if model.startswith("openrouter/"):
+            remainder = model[len("openrouter/") :]
+            if "/" in remainder:
+                model = remainder
+
         if self._supports_cache_control_in_content(model):
             messages = self._move_cache_control_to_content(messages)
 
diff --git a/tests/test_litellm/llms/openrouter/test_openrouter_provider_routing.py b/tests/test_litellm/llms/openrouter/test_openrouter_provider_routing.py
index 0815b15c873..928e2a1e0bf 100644
--- a/tests/test_litellm/llms/openrouter/test_openrouter_provider_routing.py
+++ b/tests/test_litellm/llms/openrouter/test_openrouter_provider_routing.py
@@ -100,3 +100,74 @@ class TestOpenRouterNativeModelRouting:
         )
         assert provider == "openrouter"
         assert result_model == "anthropic/claude-3.5-sonnet"
+
+
+class TestOpenRouterApiKeyResolution:
+    """api_key="os.environ/..." must be resolved even when the model takes the
+    OpenRouter early-return path (native or pre-resolved custom_llm_provider).
+    Regression introduced when the early return was added above the generic
+    os.environ resolution block.
+    """
+
+    def test_os_environ_api_key_resolved_for_native_model(self, monkeypatch):
+        monkeypatch.setenv("OPENROUTER_API_KEY_TEST", "sk-test-native-123")
+
+        _, provider, dynamic_api_key, _ = litellm.get_llm_provider(
+            model="openrouter/auto",
+            custom_llm_provider="openrouter",
+            api_key="os.environ/OPENROUTER_API_KEY_TEST",
+        )
+        assert provider == "openrouter"
+        assert dynamic_api_key == "sk-test-native-123"
+
+    def test_os_environ_api_key_resolved_for_non_native_model(self, monkeypatch):
+        monkeypatch.setenv("OPENROUTER_API_KEY_TEST", "sk-test-nonnative-456")
+
+        _, provider, dynamic_api_key, _ = litellm.get_llm_provider(
+            model="openrouter/anthropic/claude-3.5-sonnet",
+            custom_llm_provider="openrouter",
+            api_key="os.environ/OPENROUTER_API_KEY_TEST",
+        )
+        assert provider == "openrouter"
+        assert dynamic_api_key == "sk-test-nonnative-456"
+
+
+class TestOpenRouterTransformRequestDefensiveStrip:
+    """OpenrouterConfig.transform_request must strip a doubled "openrouter/"
+    prefix as a safety net for code paths that bypass get_llm_provider, while
+    preserving native single-segment IDs like "openrouter/auto".
+    """
+
+    @pytest.mark.parametrize(
+        "input_model,expected_model",
+        [
+            # Non-native: prefix must be stripped
+            (
+                "openrouter/anthropic/claude-3.5-sonnet",
+                "anthropic/claude-3.5-sonnet",
+            ),
+            (
+                "openrouter/meta-llama/llama-3-70b-instruct",
+                "meta-llama/llama-3-70b-instruct",
+            ),
+            # Native: prefix must be preserved
+            ("openrouter/auto", "openrouter/auto"),
+            ("openrouter/free", "openrouter/free"),
+            # No prefix: unchanged
+            ("anthropic/claude-3.5-sonnet", "anthropic/claude-3.5-sonnet"),
+        ],
+    )
+    def test_transform_request_strips_non_native_prefix(
+        self, input_model, expected_model
+    ):
+        from litellm.llms.openrouter.chat.transformation import OpenrouterConfig
+
+        config = OpenrouterConfig()
+        result = config.transform_request(
+            model=input_model,
+            messages=[{"role": "user", "content": "hi"}],
+            optional_params={},
+            litellm_params={},
+            headers={},
+        )
+        assert result["model"] == expected_model