diff --git a/src/openai/_client.py b/src/openai/_client.py
index 499a62dfe5..19184f7fd6 100644
--- a/src/openai/_client.py
+++ b/src/openai/_client.py
@@ -163,6 +163,7 @@ def __init__(
 
         self.workload_identity = workload_identity
 
+        _api_key_explicitly_set = api_key is not None
         if workload_identity is not None:
             self.api_key = WORKLOAD_IDENTITY_API_KEY_PLACEHOLDER
             self._api_key_provider = None
@@ -187,6 +188,7 @@ def __init__(
         if (
             _enforce_credentials
             and not self.api_key
+            and not _api_key_explicitly_set
             and self._api_key_provider is None
             and workload_identity is None
             and self.admin_api_key is None
@@ -669,6 +671,7 @@ def __init__(
 
         self.workload_identity = workload_identity
 
+        _api_key_explicitly_set = api_key is not None
         if workload_identity is not None:
             self.api_key = WORKLOAD_IDENTITY_API_KEY_PLACEHOLDER
             self._api_key_provider = None
@@ -693,6 +696,7 @@ def __init__(
         if (
             _enforce_credentials
             and not self.api_key
+            and not _api_key_explicitly_set
             and self._api_key_provider is None
             and workload_identity is None
             and self.admin_api_key is None
diff --git a/tests/test_client.py b/tests/test_client.py
index e2bb6ea966..b2e57437fe 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -524,6 +524,33 @@ def test_validate_headers(self) -> None:
             with pytest.raises(OpenAIError, match="Missing credentials"):
                 OpenAI(base_url=base_url, api_key=None, admin_api_key=None, _strict_response_validation=True)
 
+        # Explicitly passing api_key="" should not raise, even with _enforce_credentials=True.
+        # This is important for OpenAI-compatible local servers that don't require authentication.
+        with update_env(
+            **{
+                "OPENAI_API_KEY": Omit(),
+                "OPENAI_ADMIN_KEY": Omit(),
+            }
+        ):
+            client = OpenAI(
+                base_url=base_url,
+                api_key="",
+                admin_api_key=None,
+                _strict_response_validation=True,
+            )
+            assert client.api_key == ""
+
+        # OPENAI_API_KEY="" in the environment (without explicit api_key arg) should still raise,
+        # as an empty env var likely indicates misconfiguration rather than intentional use.
+        with update_env(
+            **{
+                "OPENAI_API_KEY": "",
+                "OPENAI_ADMIN_KEY": Omit(),
+            }
+        ):
+            with pytest.raises(OpenAIError, match="Missing credentials"):
+                OpenAI(base_url=base_url, admin_api_key=None, _strict_response_validation=True)
+
     @pytest.mark.respx(base_url=base_url)
     def test_api_key_provider_preserves_admin_auth(self, respx_mock: MockRouter) -> None:
         respx_mock.get("/organization/projects").mock(return_value=httpx.Response(200, json={"ok": True}))
@@ -1788,6 +1815,33 @@ async def test_validate_headers(self) -> None:
             with pytest.raises(OpenAIError, match="Missing credentials"):
                 AsyncOpenAI(base_url=base_url, api_key=None, admin_api_key=None, _strict_response_validation=True)
 
+        # Explicitly passing api_key="" should not raise, even with _enforce_credentials=True.
+        # This is important for OpenAI-compatible local servers that don't require authentication.
+        with update_env(
+            **{
+                "OPENAI_API_KEY": Omit(),
+                "OPENAI_ADMIN_KEY": Omit(),
+            }
+        ):
+            client = AsyncOpenAI(
+                base_url=base_url,
+                api_key="",
+                admin_api_key=None,
+                _strict_response_validation=True,
+            )
+            assert client.api_key == ""
+
+        # OPENAI_API_KEY="" in the environment (without explicit api_key arg) should still raise,
+        # as an empty env var likely indicates misconfiguration rather than intentional use.
+        with update_env(
+            **{
+                "OPENAI_API_KEY": "",
+                "OPENAI_ADMIN_KEY": Omit(),
+            }
+        ):
+            with pytest.raises(OpenAIError, match="Missing credentials"):
+                AsyncOpenAI(base_url=base_url, admin_api_key=None, _strict_response_validation=True)
+
     @pytest.mark.respx(base_url=base_url)
     async def test_api_key_provider_preserves_admin_auth(self, respx_mock: MockRouter) -> None:
         respx_mock.get("/organization/projects").mock(return_value=httpx.Response(200, json={"ok": True}))