diff --git a/libs/partners/anthropic/langchain_anthropic/chat_models.py b/libs/partners/anthropic/langchain_anthropic/chat_models.py
index fe51eb69a3..3d0452a92d 100644
--- a/libs/partners/anthropic/langchain_anthropic/chat_models.py
+++ b/libs/partners/anthropic/langchain_anthropic/chat_models.py
@@ -78,6 +78,11 @@ _message_type_lookups = {
 _MODEL_PROFILES = cast(ModelProfileRegistry, _PROFILES)
 
 _LANGSMITH_GATEWAY_DEFAULT_URL = "https://gateway.smith.langchain.com/anthropic"
+_LANGSMITH_GATEWAY_API_KEY_ENV_VARS = (
+    "LANGSMITH_GATEWAY_API_KEY",
+    "LANGSMITH_API_KEY",
+    "LANGCHAIN_API_KEY",
+)
 
 
 def _resolve_gateway_base_url() -> str | None:
@@ -89,6 +94,10 @@ def _resolve_gateway_base_url() -> str | None:
     return raw
 
 
+def _resolve_gateway_api_key() -> SecretStr | None:
+    return secret_from_env(_LANGSMITH_GATEWAY_API_KEY_ENV_VARS, default=None)()
+
+
 _USER_AGENT: Final[str] = f"langchain-anthropic/{__version__}"
 
 
@@ -974,18 +983,17 @@ class ChatAnthropic(BaseChatModel):
 
     anthropic_api_key: SecretStr = Field(
         alias="api_key",
-        default_factory=lambda: SecretStr(
-            (
-                os.getenv("LANGSMITH_GATEWAY_API_KEY")
-                if _resolve_gateway_base_url() is not None
-                else None
-            )
-            or secret_from_env("ANTHROPIC_API_KEY", default="")().get_secret_value()
-        ),
+        default_factory=lambda: (
+            _resolve_gateway_api_key()
+            if _resolve_gateway_base_url() is not None
+            else None
+        )
+        or secret_from_env("ANTHROPIC_API_KEY", default="")(),
     )
     """Automatically read from env var `ANTHROPIC_API_KEY` if not provided.
 
-    If `LANGSMITH_GATEWAY` is enabled, `LANGSMITH_GATEWAY_API_KEY` takes precedence.
+    If `LANGSMITH_GATEWAY` is enabled, `LANGSMITH_GATEWAY_API_KEY`,
+    `LANGSMITH_API_KEY`, and `LANGCHAIN_API_KEY` take precedence.
     """
 
     anthropic_proxy: str | None = Field(
diff --git a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
index 420ee57159..d6bffbd517 100644
--- a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
+++ b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
@@ -3608,6 +3608,47 @@ def test_langsmith_gateway_api_key(monkeypatch: pytest.MonkeyPatch) -> None:
     assert llm.anthropic_api_key.get_secret_value() == "gateway-key"
 
 
+@pytest.mark.parametrize(
+    ("env_var", "expected"),
+    [
+        ("LANGSMITH_API_KEY", "langsmith-key"),
+        ("LANGCHAIN_API_KEY", "langchain-key"),
+    ],
+)
+def test_langsmith_gateway_api_key_langsmith_fallbacks(
+    monkeypatch: pytest.MonkeyPatch, env_var: str, expected: str
+) -> None:
+    monkeypatch.setenv("LANGSMITH_GATEWAY", "true")
+    monkeypatch.delenv("LANGSMITH_GATEWAY_API_KEY", raising=False)
+    monkeypatch.delenv("LANGSMITH_API_KEY", raising=False)
+    monkeypatch.delenv("LANGCHAIN_API_KEY", raising=False)
+    monkeypatch.delenv("ANTHROPIC_API_KEY", raising=False)
+    monkeypatch.setenv(env_var, expected)
+    llm = ChatAnthropic(model=MODEL_NAME)
+    assert llm.anthropic_api_key.get_secret_value() == expected
+
+
+def test_langsmith_gateway_api_key_precedence(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv("LANGSMITH_GATEWAY", "true")
+    monkeypatch.setenv("LANGSMITH_GATEWAY_API_KEY", "gateway-key")
+    monkeypatch.setenv("LANGSMITH_API_KEY", "langsmith-key")
+    monkeypatch.setenv("LANGCHAIN_API_KEY", "langchain-key")
+    monkeypatch.setenv("ANTHROPIC_API_KEY", "provider-key")
+    llm = ChatAnthropic(model=MODEL_NAME)
+    assert llm.anthropic_api_key.get_secret_value() == "gateway-key"
+
+
+def test_langsmith_gateway_explicit_api_key_takes_precedence(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv("LANGSMITH_GATEWAY", "true")
+    monkeypatch.setenv("LANGSMITH_GATEWAY_API_KEY", "gateway-key")
+    llm = ChatAnthropic(model=MODEL_NAME, api_key="explicit-key")
+    assert llm.anthropic_api_key.get_secret_value() == "explicit-key"
+
+
 def test_langsmith_gateway_api_key_not_used_without_gateway(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
diff --git a/libs/partners/fireworks/langchain_fireworks/chat_models.py b/libs/partners/fireworks/langchain_fireworks/chat_models.py
index af530d254d..f8020bd023 100644
--- a/libs/partners/fireworks/langchain_fireworks/chat_models.py
+++ b/libs/partners/fireworks/langchain_fireworks/chat_models.py
@@ -110,6 +110,11 @@ logger = logging.getLogger(__name__)
 _MODEL_PROFILES = cast("ModelProfileRegistry", _PROFILES)
 
 _LANGSMITH_GATEWAY_DEFAULT_URL = "https://gateway.smith.langchain.com/fireworks"
+_LANGSMITH_GATEWAY_API_KEY_ENV_VARS = (
+    "LANGSMITH_GATEWAY_API_KEY",
+    "LANGSMITH_API_KEY",
+    "LANGCHAIN_API_KEY",
+)
 
 
 def _resolve_gateway_base_url() -> str | None:
@@ -121,6 +126,10 @@ def _resolve_gateway_base_url() -> str | None:
     return raw
 
 
+def _resolve_gateway_api_key() -> SecretStr | None:
+    return secret_from_env(_LANGSMITH_GATEWAY_API_KEY_ENV_VARS, default=None)()
+
+
 def _get_default_model_profile(model_name: str) -> ModelProfile:
     default = _MODEL_PROFILES.get(model_name) or {}
     return default.copy()
@@ -768,27 +777,26 @@ class ChatFireworks(BaseChatModel):
 
     fireworks_api_key: SecretStr = Field(
         alias="api_key",
-        default_factory=lambda: SecretStr(
-            (
-                os.getenv("LANGSMITH_GATEWAY_API_KEY")
-                if _resolve_gateway_base_url() is not None
-                else None
-            )
-            or secret_from_env(
-                "FIREWORKS_API_KEY",
-                error_message=(
-                    "You must specify an api key. "
-                    "You can pass it an argument as `api_key=...` or "
-                    "set the environment variable `FIREWORKS_API_KEY`."
-                ),
-            )().get_secret_value()
-        ),
+        default_factory=lambda: (
+            _resolve_gateway_api_key()
+            if _resolve_gateway_base_url() is not None
+            else None
+        )
+        or secret_from_env(
+            "FIREWORKS_API_KEY",
+            error_message=(
+                "You must specify an api key. "
+                "You can pass it an argument as `api_key=...` or "
+                "set the environment variable `FIREWORKS_API_KEY`."
+            ),
+        )(),
     )
     """Fireworks API key.
 
     Automatically read from env variable `FIREWORKS_API_KEY` if not provided.
 
-    If `LANGSMITH_GATEWAY` is enabled, `LANGSMITH_GATEWAY_API_KEY` takes precedence.
+    If `LANGSMITH_GATEWAY` is enabled, `LANGSMITH_GATEWAY_API_KEY`,
+    `LANGSMITH_API_KEY`, and `LANGCHAIN_API_KEY` take precedence.
     """
 
     fireworks_api_base: str | None = Field(
diff --git a/libs/partners/fireworks/tests/unit_tests/test_chat_models.py b/libs/partners/fireworks/tests/unit_tests/test_chat_models.py
index a8ef4a6431..18eecfac67 100644
--- a/libs/partners/fireworks/tests/unit_tests/test_chat_models.py
+++ b/libs/partners/fireworks/tests/unit_tests/test_chat_models.py
@@ -1621,6 +1621,47 @@ def test_langsmith_gateway_api_key(monkeypatch: pytest.MonkeyPatch) -> None:
     assert llm.fireworks_api_key.get_secret_value() == "gateway-key"
 
 
+@pytest.mark.parametrize(
+    ("env_var", "expected"),
+    [
+        ("LANGSMITH_API_KEY", "langsmith-key"),
+        ("LANGCHAIN_API_KEY", "langchain-key"),
+    ],
+)
+def test_langsmith_gateway_api_key_langsmith_fallbacks(
+    monkeypatch: pytest.MonkeyPatch, env_var: str, expected: str
+) -> None:
+    monkeypatch.setenv("LANGSMITH_GATEWAY", "true")
+    monkeypatch.delenv("LANGSMITH_GATEWAY_API_KEY", raising=False)
+    monkeypatch.delenv("LANGSMITH_API_KEY", raising=False)
+    monkeypatch.delenv("LANGCHAIN_API_KEY", raising=False)
+    monkeypatch.delenv("FIREWORKS_API_KEY", raising=False)
+    monkeypatch.setenv(env_var, expected)
+    llm = ChatFireworks(model=MODEL_NAME)  # type: ignore[call-arg]
+    assert llm.fireworks_api_key.get_secret_value() == expected
+
+
+def test_langsmith_gateway_api_key_precedence(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv("LANGSMITH_GATEWAY", "true")
+    monkeypatch.setenv("LANGSMITH_GATEWAY_API_KEY", "gateway-key")
+    monkeypatch.setenv("LANGSMITH_API_KEY", "langsmith-key")
+    monkeypatch.setenv("LANGCHAIN_API_KEY", "langchain-key")
+    monkeypatch.setenv("FIREWORKS_API_KEY", "provider-key")
+    llm = ChatFireworks(model=MODEL_NAME)  # type: ignore[call-arg]
+    assert llm.fireworks_api_key.get_secret_value() == "gateway-key"
+
+
+def test_langsmith_gateway_explicit_api_key_takes_precedence(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv("LANGSMITH_GATEWAY", "true")
+    monkeypatch.setenv("LANGSMITH_GATEWAY_API_KEY", "gateway-key")
+    llm = ChatFireworks(model=MODEL_NAME, api_key="explicit-key")  # type: ignore[call-arg]
+    assert llm.fireworks_api_key.get_secret_value() == "explicit-key"
+
+
 def test_langsmith_gateway_api_key_not_used_without_gateway(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
diff --git a/libs/partners/openai/langchain_openai/chat_models/base.py b/libs/partners/openai/langchain_openai/chat_models/base.py
index 4588a2527f..1dedec3ccd 100644
--- a/libs/partners/openai/langchain_openai/chat_models/base.py
+++ b/libs/partners/openai/langchain_openai/chat_models/base.py
@@ -179,6 +179,11 @@ def _get_ssrf_safe_client() -> httpx.Client:
 _MODEL_PROFILES = cast(ModelProfileRegistry, _PROFILES)
 
 _LANGSMITH_GATEWAY_DEFAULT_URL = "https://gateway.smith.langchain.com/openai/v1"
+_LANGSMITH_GATEWAY_API_KEY_ENV_VARS = (
+    "LANGSMITH_GATEWAY_API_KEY",
+    "LANGSMITH_API_KEY",
+    "LANGCHAIN_API_KEY",
+)
 
 
 def _resolve_gateway_base_url() -> str | None:
@@ -190,6 +195,10 @@ def _resolve_gateway_base_url() -> str | None:
     return raw
 
 
+def _resolve_gateway_api_key() -> SecretStr | None:
+    return secret_from_env(_LANGSMITH_GATEWAY_API_KEY_ENV_VARS, default=None)()
+
+
 def _get_default_model_profile(model_name: str) -> ModelProfile:
     default = _MODEL_PROFILES.get(model_name) or {}
     return default.copy()
@@ -1212,10 +1221,11 @@ class BaseChatOpenAI(BaseChatModel):
         sync_api_key_value: str | Callable[[], str] | None = None
         async_api_key_value: str | Callable[[], Awaitable[str]] | None = None
 
-        if self.openai_api_key is None and _base_url_from_gateway:
-            gateway_api_key = os.getenv("LANGSMITH_GATEWAY_API_KEY")
+        explicit_api_key = bool({"api_key", "openai_api_key"} & self.model_fields_set)
+        if _base_url_from_gateway and not explicit_api_key:
+            gateway_api_key = _resolve_gateway_api_key()
             if gateway_api_key is not None:
-                self.openai_api_key = SecretStr(gateway_api_key)
+                self.openai_api_key = gateway_api_key
 
         if self.openai_api_key is not None:
             # Because OpenAI and AsyncOpenAI clients support either sync or async
diff --git a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
index dc38e603c5..c47eaa8a37 100644
--- a/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
+++ b/libs/partners/openai/tests/unit_tests/chat_models/test_base.py
@@ -4531,6 +4531,50 @@ def test_langsmith_gateway_api_key(monkeypatch: pytest.MonkeyPatch) -> None:
     assert llm.openai_api_key.get_secret_value() == "gateway-key"
 
 
+@pytest.mark.parametrize(
+    ("env_var", "expected"),
+    [
+        ("LANGSMITH_API_KEY", "langsmith-key"),
+        ("LANGCHAIN_API_KEY", "langchain-key"),
+    ],
+)
+def test_langsmith_gateway_api_key_langsmith_fallbacks(
+    monkeypatch: pytest.MonkeyPatch, env_var: str, expected: str
+) -> None:
+    monkeypatch.setenv("LANGSMITH_GATEWAY", "true")
+    monkeypatch.delenv("LANGSMITH_GATEWAY_API_KEY", raising=False)
+    monkeypatch.delenv("LANGSMITH_API_KEY", raising=False)
+    monkeypatch.delenv("LANGCHAIN_API_KEY", raising=False)
+    monkeypatch.delenv("OPENAI_API_KEY", raising=False)
+    monkeypatch.setenv(env_var, expected)
+    llm = ChatOpenAI(model=OPENAI_TEST_MODEL)
+    assert isinstance(llm.openai_api_key, SecretStr)
+    assert llm.openai_api_key.get_secret_value() == expected
+
+
+def test_langsmith_gateway_api_key_precedence(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv("LANGSMITH_GATEWAY", "true")
+    monkeypatch.setenv("LANGSMITH_GATEWAY_API_KEY", "gateway-key")
+    monkeypatch.setenv("LANGSMITH_API_KEY", "langsmith-key")
+    monkeypatch.setenv("LANGCHAIN_API_KEY", "langchain-key")
+    monkeypatch.setenv("OPENAI_API_KEY", "provider-key")
+    llm = ChatOpenAI(model=OPENAI_TEST_MODEL)
+    assert isinstance(llm.openai_api_key, SecretStr)
+    assert llm.openai_api_key.get_secret_value() == "gateway-key"
+
+
+def test_langsmith_gateway_explicit_api_key_takes_precedence(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv("LANGSMITH_GATEWAY", "true")
+    monkeypatch.setenv("LANGSMITH_GATEWAY_API_KEY", "gateway-key")
+    llm = ChatOpenAI(model=OPENAI_TEST_MODEL, api_key="explicit-key")
+    assert isinstance(llm.openai_api_key, SecretStr)
+    assert llm.openai_api_key.get_secret_value() == "explicit-key"
+
+
 def test_langsmith_gateway_api_key_not_used_without_gateway(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None: