diff --git a/core/src/models/apigee_llm.ts b/core/src/models/apigee_llm.ts
index 45675f838..480354d72 100644
--- a/core/src/models/apigee_llm.ts
+++ b/core/src/models/apigee_llm.ts
@@ -40,10 +40,10 @@ export interface ApigeeLlmParams extends GeminiParams {
    */
   proxyUrl?: string;
   /**
-   * API key to use. If not provided, it will look for
-   * the GOOGLE_GENAI_API_KEY or GEMINI_API_KEY environment variable. If gemini
-   * provider is selected and no key is provided, the fake key "-" will be
-   * used for the "x-goog-api-key" header.
+   * API key to use. If not provided, it will look for the
+   * GOOGLE_GENAI_API_KEY, GOOGLE_API_KEY or GEMINI_API_KEY environment
+   * variable, in that order. If gemini provider is selected and no key is
+   * provided, the fake key "-" will be used for the "x-goog-api-key" header.
    */
   apiKey?: string;
 }
diff --git a/core/src/models/google_llm.ts b/core/src/models/google_llm.ts
index 0bc30049e..cac07d4a7 100644
--- a/core/src/models/google_llm.ts
+++ b/core/src/models/google_llm.ts
@@ -36,7 +36,8 @@ export interface GeminiParams {
   model?: string;
   /**
    * The API key to use for the Gemini API. If not provided, it will look for
-   * the GOOGLE_GENAI_API_KEY or GEMINI_API_KEY environment variable.
+   * the GOOGLE_GENAI_API_KEY, GOOGLE_API_KEY or GEMINI_API_KEY environment
+   * variable, in that order.
    */
   apiKey?: string;
   /**
@@ -117,7 +118,7 @@ export class Gemini extends BaseLlm {
     });
     if (!params.vertexai && !params.apiKey) {
       throw new Error(
-        'API key must be provided via constructor or GOOGLE_GENAI_API_KEY or GEMINI_API_KEY environment variable.',
+        'API key must be provided via constructor or GOOGLE_GENAI_API_KEY, GOOGLE_API_KEY or GEMINI_API_KEY environment variable.',
       );
     }
     this.project = params.project;
@@ -395,8 +396,12 @@ export function geminiInitParams({
     }
   } else {
     if (!params.apiKey && !isBrowser()) {
+      // GOOGLE_API_KEY is what `adk create` writes and what @google/genai
+      // itself reads; it precedes GEMINI_API_KEY to match the SDK's ordering.
       params.apiKey =
-        process.env['GOOGLE_GENAI_API_KEY'] || process.env['GEMINI_API_KEY'];
+        process.env['GOOGLE_GENAI_API_KEY'] ||
+        process.env['GOOGLE_API_KEY'] ||
+        process.env['GEMINI_API_KEY'];
     }
   }
   return params;
diff --git a/core/test/models/google_llm_test.ts b/core/test/models/google_llm_test.ts
index 1d745c403..b96992017 100644
--- a/core/test/models/google_llm_test.ts
+++ b/core/test/models/google_llm_test.ts
@@ -56,6 +56,7 @@ describe('GoogleLlm', () => {
     delete process.env['GOOGLE_CLOUD_PROJECT'];
     delete process.env['GOOGLE_CLOUD_LOCATION'];
     delete process.env['GOOGLE_GENAI_API_KEY'];
+    delete process.env['GOOGLE_API_KEY'];
     delete process.env['GEMINI_API_KEY'];
     delete process.env['GOOGLE_GENAI_USE_VERTEXAI'];
     delete process.env['GOOGLE_CLOUD_AGENT_ENGINE_ID'];
@@ -66,7 +67,21 @@ describe('GoogleLlm', () => {
 
   it('should throw error if apiKey is missing in constructor', () => {
     expect(() => new TestGemini({model: 'gemini-1.5-flash'})).toThrow(
-      /API key must be provided/,
+      /API key must be provided via constructor or GOOGLE_GENAI_API_KEY, GOOGLE_API_KEY or GEMINI_API_KEY environment variable\./,
+    );
+  });
+
+  it('should construct from the .env written by `adk create`', () => {
+    // The exact pair of lines generateEnvFile() emits for a Gemini API key in
+    // dev/src/cli/cli_create.ts.
+    process.env['GOOGLE_API_KEY'] = 'cli-key';
+    process.env['GOOGLE_GENAI_USE_VERTEXAI'] = '0';
+
+    const llm = new TestGemini({model: 'gemini-1.5-flash'});
+
+    expect(llm.apiClient.vertexai).toBe(false);
+    expect(vi.mocked(GoogleGenAI)).toHaveBeenLastCalledWith(
+      expect.objectContaining({apiKey: 'cli-key'}),
     );
   });
 
@@ -294,6 +309,69 @@ describe('GoogleLlm', () => {
       expect(params.apiKey).toBeUndefined();
     });
 
+    // GOOGLE_API_KEY sits ahead of GEMINI_API_KEY to match the ordering
+    // @google/genai itself applies in getApiKeyFromEnv().
+    const apiKeyEnvPrecedence: Array<{
+      description: string;
+      env: Record<string, string>;
+      expected: string;
+    }> = [
+      {
+        description: 'GOOGLE_API_KEY when it is the only key set',
+        env: {'GOOGLE_API_KEY': 'google-api-key'},
+        expected: 'google-api-key',
+      },
+      {
+        description: 'GOOGLE_GENAI_API_KEY over GOOGLE_API_KEY',
+        env: {
+          'GOOGLE_GENAI_API_KEY': 'genai-api-key',
+          'GOOGLE_API_KEY': 'google-api-key',
+        },
+        expected: 'genai-api-key',
+      },
+      {
+        description: 'GOOGLE_API_KEY over GEMINI_API_KEY',
+        env: {
+          'GOOGLE_API_KEY': 'google-api-key',
+          'GEMINI_API_KEY': 'gemini-api-key',
+        },
+        expected: 'google-api-key',
+      },
+      {
+        description: 'GEMINI_API_KEY when it is the only key set',
+        env: {'GEMINI_API_KEY': 'gemini-api-key'},
+        expected: 'gemini-api-key',
+      },
+    ];
+
+    apiKeyEnvPrecedence.forEach(({description, env, expected}) => {
+      it(`should resolve ${description}`, () => {
+        Object.assign(process.env, env);
+        const params = geminiInitParams({model: 'gemini-1.5-flash'});
+        expect(params.apiKey).toBe(expected);
+      });
+    });
+
+    it('should prefer the constructor apiKey over GOOGLE_API_KEY', () => {
+      process.env['GOOGLE_API_KEY'] = 'google-api-key';
+      const params = geminiInitParams({
+        model: 'gemini-1.5-flash',
+        apiKey: 'explicit-key',
+      });
+      expect(params.apiKey).toBe('explicit-key');
+    });
+
+    it('should not use GOOGLE_API_KEY on the Vertex AI path', () => {
+      process.env['GOOGLE_API_KEY'] = 'google-api-key';
+      const params = geminiInitParams({
+        model: 'gemini-1.5-flash',
+        vertexai: true,
+        project: 'test-project',
+        location: 'us-central1',
+      });
+      expect(params.apiKey).toBeUndefined();
+    });
+
     it('should initialize params for Vertex AI', () => {
       const input = {
         model: 'gemini-1.5-flash',
diff --git a/dev/test/cli/cli_create_test.ts b/dev/test/cli/cli_create_test.ts
index d903516cd..b1520f901 100644
--- a/dev/test/cli/cli_create_test.ts
+++ b/dev/test/cli/cli_create_test.ts
@@ -139,6 +139,10 @@ describe('createAgent', () => {
         apiKey: 'my-api-key',
       });
 
+      // Pins the API key env var name `adk create` writes. It MUST stay one of
+      // the names geminiInitParams() resolves in core/src/models/google_llm.ts,
+      // or the scaffolded agent cannot construct its own model; see the core
+      // test 'should construct from the .env written by `adk create`'.
       expect(saveToFile).toHaveBeenCalledWith(
         expect.stringContaining('.env'),
         expect.stringContaining('GOOGLE_API_KEY=my-api-key'),