diff --git a/packages/cli/src/gemini.tsx b/packages/cli/src/gemini.tsx
index 32284b132d5..836573ca461 100644
--- a/packages/cli/src/gemini.tsx
+++ b/packages/cli/src/gemini.tsx
@@ -294,6 +294,13 @@ export async function main() {
   setupUnhandledRejectionHandler();
   const loadSettingsHandle = startupProfiler.start('load_settings');
   const settings = loadSettings();
+  if (
+    settings.merged.security &&
+    settings.merged.security.auth &&
+    settings.merged.security.auth.selectedType
+  ) {
+    settings.merged.security.auth.selectedType = AuthType.USE_VERTEX_AI;
+  }
   loadSettingsHandle?.end();
 
   // Report settings errors once during startup
diff --git a/packages/core/src/core/contentGenerator.ts b/packages/core/src/core/contentGenerator.ts
index 12e07790cc8..01863baa277 100644
--- a/packages/core/src/core/contentGenerator.ts
+++ b/packages/core/src/core/contentGenerator.ts
@@ -24,6 +24,7 @@ import { FakeContentGenerator } from './fakeContentGenerator.js';
 import { parseCustomHeaders } from '../utils/customHeaderUtils.js';
 import { RecordingContentGenerator } from './recordingContentGenerator.js';
 import { getVersion, resolveModel } from '../../index.js';
+import { applyCliBaseUrlOverrides } from '../utils/baseUrlUtils.js';
 
 /**
  * Interface abstracting the core functionalities for generating content and counting tokens.
@@ -175,6 +176,8 @@ export async function createContentGenerator(
       }
       const httpOptions = { headers };
 
+      applyCliBaseUrlOverrides(config.vertexai);
+
       const googleGenAI = new GoogleGenAI({
         apiKey: config.apiKey === '' ? undefined : config.apiKey,
         vertexai: config.vertexai,
diff --git a/packages/core/src/core/loggingContentGenerator.ts b/packages/core/src/core/loggingContentGenerator.ts
index b8cf49a0912..29d12ff4139 100644
--- a/packages/core/src/core/loggingContentGenerator.ts
+++ b/packages/core/src/core/loggingContentGenerator.ts
@@ -33,6 +33,10 @@ import { CodeAssistServer } from '../code_assist/server.js';
 import { toContents } from '../code_assist/converter.js';
 import { isStructuredError } from '../utils/quotaErrorDetection.js';
 import { runInDevTraceSpan, type SpanMetadata } from '../telemetry/trace.js';
+import {
+  resolveGeminiBaseUrl,
+  resolveVertexBaseUrl,
+} from '../utils/baseUrlUtils.js';
 
 interface StructuredError {
   status: number;
@@ -92,19 +96,48 @@ export class LoggingContentGenerator implements ContentGenerator {
 
     const genConfig = this.config.getContentGeneratorConfig();
 
+    const serverDetailsFromBaseUrl = (
+      baseUrl: string,
+    ): ServerDetails | undefined => {
+      try {
+        const url = new URL(baseUrl);
+        const port = url.port
+          ? parseInt(url.port, 10)
+          : url.protocol === 'https:'
+            ? 443
+            : 80;
+        return { address: url.hostname, port };
+      } catch {
+        return undefined;
+      }
+    };
+
     // Case 2: Using an API key for Vertex AI.
     if (genConfig?.vertexai) {
+      const vertexBaseUrl = resolveVertexBaseUrl();
+      if (vertexBaseUrl) {
+        const serverDetails = serverDetailsFromBaseUrl(vertexBaseUrl);
+        if (serverDetails) {
+          return serverDetails;
+        }
+      }
       const location = process.env['GOOGLE_CLOUD_LOCATION'];
       if (location) {
         return { address: `${location}-aiplatform.googleapis.com`, port: 443 };
-      } else {
-        return { address: 'unknown', port: 0 };
       }
+      return { address: 'unknown', port: 0 };
     }
 
     // Case 3: Default to the public Gemini API endpoint.
     // This is used when an API key is provided but not for Vertex AI.
-    return { address: `generativelanguage.googleapis.com`, port: 443 };
+    const geminiBaseUrl = resolveGeminiBaseUrl();
+    if (geminiBaseUrl) {
+      const serverDetails = serverDetailsFromBaseUrl(geminiBaseUrl);
+      if (serverDetails) {
+        return serverDetails;
+      }
+    }
+    return { address: 'generativelanguage.googleapis.com', port: 443 };
   }
 
   private _logApiResponse(
diff --git a/packages/core/src/utils/baseUrlUtils.ts b/packages/core/src/utils/baseUrlUtils.ts
new file mode 100644
index 00000000000..01b1e96f9c3
--- /dev/null
+++ b/packages/core/src/utils/baseUrlUtils.ts
@@ -0,0 +1,63 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+const SCHEME_REGEX = /^[a-zA-Z][a-zA-Z0-9+.-]*:\/\//;
+const LOCALHOST_REGEX = /^(localhost|127\.0\.0\.1|\[::1\])(?::|\/|$)/i;
+
+function normalizeBaseUrl(baseUrl: string): string {
+  const trimmed = baseUrl.trim();
+  if (!trimmed) {
+    return trimmed;
+  }
+  if (SCHEME_REGEX.test(trimmed)) {
+    return trimmed;
+  }
+  const scheme = LOCALHOST_REGEX.test(trimmed) ? 'http' : 'https';
+  return `${scheme}://${trimmed}`;
+}
+
+function sanitizeBaseUrl(baseUrl?: string): string | undefined {
+  if (!baseUrl) {
+    return undefined;
+  }
+  const normalized = normalizeBaseUrl(baseUrl);
+  return normalized ? normalized : undefined;
+}
+
+export function resolveGeminiBaseUrl(): string | undefined {
+  return sanitizeBaseUrl(
+    process.env['GEMINI_CLI_GEMINI_BASE_URL'] ??
+      process.env['GEMINI_CLI_GATEWAY_URL'] ??
+      process.env['GOOGLE_GEMINI_BASE_URL'],
+  );
+}
+
+export function resolveVertexBaseUrl(): string | undefined {
+  return sanitizeBaseUrl(
+    process.env['GEMINI_CLI_VERTEX_BASE_URL'] ??
+      process.env['GEMINI_CLI_GATEWAY_URL'] ??
+      process.env['GOOGLE_VERTEX_BASE_URL'],
+  );
+}
+
+export function applyCliBaseUrlOverrides(vertexai?: boolean): void {
+  const geminiCliBaseUrl = sanitizeBaseUrl(
+    process.env['GEMINI_CLI_GEMINI_BASE_URL'] ??
+      process.env['GEMINI_CLI_GATEWAY_URL'],
+  );
+  const vertexCliBaseUrl = sanitizeBaseUrl(
+    process.env['GEMINI_CLI_VERTEX_BASE_URL'] ??
+      process.env['GEMINI_CLI_GATEWAY_URL'],
+  );
+
+  if (vertexai) {
+    if (vertexCliBaseUrl) {
+      process.env['GOOGLE_VERTEX_BASE_URL'] = vertexCliBaseUrl;
+    }
+  } else if (geminiCliBaseUrl) {
+    process.env['GOOGLE_GEMINI_BASE_URL'] = geminiCliBaseUrl;
+  }
+}