1 files changed, 75 insertions, 0 deletions
diff --git a/packages/cli/src/utils/modelCheck.ts b/packages/cli/src/utils/modelCheck.ts
new file mode 100644
index 00000000..1634656e
--- /dev/null
+++ b/packages/cli/src/utils/modelCheck.ts
@@ -0,0 +1,75 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {
+  DEFAULT_GEMINI_MODEL,
+  DEFAULT_GEMINI_FLASH_MODEL,
+} from '../config/config.js';
+
+export interface EffectiveModelCheckResult {
+  effectiveModel: string;
+  switched: boolean;
+  originalModelIfSwitched?: string;
+}
+
+/**
+ * Checks if the default "pro" model is rate-limited and returns a fallback "flash"
+ * model if necessary. This function is designed to be silent.
+ * @param apiKey The API key to use for the check.
+ * @param currentConfiguredModel The model currently configured in settings.
+ * @returns An object indicating the model to use, whether a switch occurred,
+ *          and the original model if a switch happened.
+ */
+export async function getEffectiveModel(
+  apiKey: string,
+  currentConfiguredModel: string,
+): Promise<EffectiveModelCheckResult> {
+  if (currentConfiguredModel !== DEFAULT_GEMINI_MODEL) {
+    // Only check if the user is trying to use the specific pro model we want to fallback from.
+    return { effectiveModel: currentConfiguredModel, switched: false };
+  }
+
+  const modelToTest = DEFAULT_GEMINI_MODEL;
+  const fallbackModel = DEFAULT_GEMINI_FLASH_MODEL;
+  const endpoint = `https://generativelanguage.googleapis.com/v1beta/models/${modelToTest}:generateContent?key=${apiKey}`;
+  const body = JSON.stringify({
+    contents: [{ parts: [{ text: 'test' }] }],
+    generationConfig: {
+      maxOutputTokens: 1,
+      temperature: 0,
+      topK: 1,
+      thinkingConfig: { thinkingBudget: 0, includeThoughts: false },
+    },
+  });
+
+  const controller = new AbortController();
+  const timeoutId = setTimeout(() => controller.abort(), 2000); // 500ms timeout for the request
+
+  try {
+    const response = await fetch(endpoint, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body,
+      signal: controller.signal,
+    });
+
+    clearTimeout(timeoutId);
+
+    if (response.status === 429) {
+      return {
+        effectiveModel: fallbackModel,
+        switched: true,
+        originalModelIfSwitched: modelToTest,
+      };
+    }
+    // For any other case (success, other error codes), we stick to the original model.
+    return { effectiveModel: currentConfiguredModel, switched: false };
+  } catch (_error) {
+    clearTimeout(timeoutId);
+    // On timeout or any other fetch error, stick to the original model.
+    return { effectiveModel: currentConfiguredModel, switched: false };
+  }
+}