diff --git a/app.py b/app.py
index 463f7e1..063bdd5 100644
--- a/app.py
+++ b/app.py
@@ -289,7 +289,10 @@ def _openai_client_for(provider: str, base_url: str | None):
     from openai import OpenAI
 
     final_base_url = resolve_provider_base_url(provider, base_url)
-    api_key = os.environ.get("OPENAI_API_KEY", "dev-local")
+    if provider and provider.lower() == "lmstudio":
+        api_key = os.environ.get("OPENAI_API_KEY") or "lmstudio-local"
+    else:
+        api_key = os.environ.get("OPENAI_API_KEY", "dev-local")
     return OpenAI(api_key=api_key, base_url=final_base_url)
 
 
diff --git a/tests/contracts/test_control_plane_endpoints.py b/tests/contracts/test_control_plane_endpoints.py
index d991b33..a83bfcc 100644
--- a/tests/contracts/test_control_plane_endpoints.py
+++ b/tests/contracts/test_control_plane_endpoints.py
@@ -1,6 +1,7 @@
 import pytest
+from types import SimpleNamespace
 
-from app import app
+from app import app, _openai_client_for
 
 pytestmark = pytest.mark.contracts
 
@@ -36,3 +37,64 @@ def test_ai_test_provider_mock():
         r = client.post("/api/ai/test_provider", json={"provider": "mock", "model": "mock-model"})
     assert r.status_code == 200
     assert r.get_json()["ok"] is True
+
+
+def test_ai_test_provider_lmstudio_allows_empty_env_api_key(monkeypatch):
+    captured = {}
+
+    class _FakeModels:
+        @staticmethod
+        def list():
+            return SimpleNamespace(data=[SimpleNamespace(id="local-model")])
+
+    class _FakeCompletions:
+        @staticmethod
+        def create(**_kwargs):
+            return SimpleNamespace(
+                choices=[SimpleNamespace(message=SimpleNamespace(content="ok"))]
+            )
+
+    class _FakeChat:
+        completions = _FakeCompletions()
+
+    class _FakeOpenAI:
+        def __init__(self, api_key, base_url):
+            captured["api_key"] = api_key
+            captured["base_url"] = base_url
+            self.models = _FakeModels()
+            self.chat = _FakeChat()
+
+    monkeypatch.setenv("OPENAI_API_KEY", "")
+    monkeypatch.setattr("openai.OpenAI", _FakeOpenAI)
+
+    with app.test_client() as client:
+        r = client.post(
+            "/api/ai/test_provider",
+            json={
+                "provider": "lmstudio",
+                "base_url": "http://localhost:1234/v1",
+                "model": "local-model",
+            },
+        )
+    assert r.status_code == 200
+    assert r.get_json()["ok"] is True
+    assert captured["api_key"] == "lmstudio-local"
+
+
+@pytest.mark.parametrize("provider", ["openai", "ollama", "openrouter"])
+def test_openai_client_for_non_lmstudio_keeps_existing_env_behavior(
+    monkeypatch, provider
+):
+    captured = {}
+
+    class _FakeOpenAI:
+        def __init__(self, api_key, base_url):
+            captured["api_key"] = api_key
+            captured["base_url"] = base_url
+
+    monkeypatch.setenv("OPENAI_API_KEY", "")
+    monkeypatch.setattr("openai.OpenAI", _FakeOpenAI)
+
+    _openai_client_for(provider, None)
+
+    assert captured["api_key"] == ""