diff --git a/src/agents/model-auth-env.ts b/src/agents/model-auth-env.ts
index 71e5a44d593..5c1d8800f3d 100644
--- a/src/agents/model-auth-env.ts
+++ b/src/agents/model-auth-env.ts
@@ -70,7 +70,9 @@ export function resolveEnvApiKey(
         return resolved;
       }
     }
-    return null;
+    if (normalized !== "google-vertex") {
+      return null;
+    }
   }
 
   if (normalized === "google-vertex") {
diff --git a/src/agents/model-auth.profiles.test.ts b/src/agents/model-auth.profiles.test.ts
index 23819b70cca..99baf9c435e 100644
--- a/src/agents/model-auth.profiles.test.ts
+++ b/src/agents/model-auth.profiles.test.ts
@@ -827,6 +827,29 @@ describe("getApiKeyForModel", () => {
     });
   });
 
+  it("resolveEnvApiKey('google-vertex') keeps ADC fallback when manifest env candidates are empty", async () => {
+    const tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "openclaw-google-adc-candidates-"));
+    const credentialsPath = path.join(tempDir, "adc.json");
+    await fs.writeFile(credentialsPath, "{}", "utf8");
+
+    try {
+      const resolved = resolveEnvApiKey(
+        "google-vertex",
+        {
+          GOOGLE_APPLICATION_CREDENTIALS: credentialsPath,
+          GOOGLE_CLOUD_LOCATION: "us-central1",
+          GOOGLE_CLOUD_PROJECT: "vertex-project",
+        } as NodeJS.ProcessEnv,
+        { candidateMap: { "google-vertex": ["GOOGLE_CLOUD_API_KEY"] } },
+      );
+
+      expect(resolved?.apiKey).toBe("gcp-vertex-credentials");
+      expect(resolved?.source).toBe("gcloud adc");
+    } finally {
+      await fs.rm(tempDir, { recursive: true, force: true });
+    }
+  });
+
   it("resolveEnvApiKey('anthropic-vertex') accepts GOOGLE_APPLICATION_CREDENTIALS with project_id", async () => {
     await expectVertexAdcEnvApiKey({
       provider: "anthropic-vertex",