fix(patch): cherry-pick 37f128a to release/v0.28.0-pr-18478 (#18821)

Co-authored-by: matt korwel <matt.korwel@gmail.com>

packages/core/src/config/models.test.ts

@@ -8,6 +8,7 @@ import { describe, it, expect } from 'vitest';
 import {
   resolveModel,
   resolveClassifierModel,
+  isGemini3Model,
   isGemini2Model,
   isAutoModel,
   getDisplayString,
@@ -25,6 +26,29 @@ import {
   DEFAULT_GEMINI_MODEL_AUTO,
 } from './models.js';
 
+describe('isGemini3Model', () => {
+  it('should return true for gemini-3 models', () => {
+    expect(isGemini3Model('gemini-3-pro-preview')).toBe(true);
+    expect(isGemini3Model('gemini-3-flash-preview')).toBe(true);
+  });
+
+  it('should return true for aliases that resolve to Gemini 3 when preview is enabled', () => {
+    expect(isGemini3Model(GEMINI_MODEL_ALIAS_AUTO, true)).toBe(true);
+    expect(isGemini3Model(GEMINI_MODEL_ALIAS_PRO, true)).toBe(true);
+    expect(isGemini3Model(PREVIEW_GEMINI_MODEL_AUTO)).toBe(true);
+  });
+
+  it('should return false for Gemini 2 models', () => {
+    expect(isGemini3Model('gemini-2.5-pro')).toBe(false);
+    expect(isGemini3Model('gemini-2.5-flash')).toBe(false);
+    expect(isGemini3Model(DEFAULT_GEMINI_MODEL_AUTO)).toBe(false);
+  });
+
+  it('should return false for arbitrary strings', () => {
+    expect(isGemini3Model('gpt-4')).toBe(false);
+  });
+});
+
 describe('getDisplayString', () => {
   it('should return Auto (Gemini 3) for preview auto model', () => {
     expect(getDisplayString(PREVIEW_GEMINI_MODEL_AUTO)).toBe('Auto (Gemini 3)');

packages/core/src/config/models.ts

@@ -137,6 +137,20 @@ export function isPreviewModel(model: string): boolean {
   );
 }
 
+/**
+ * Checks if the model is a Gemini 3 model.
+ *
+ * @param model The model name to check.
+ * @returns True if the model is a Gemini 3 model.
+ */
+export function isGemini3Model(
+  model: string,
+  previewFeaturesEnabled = false,
+): boolean {
+  const resolved = resolveModel(model, previewFeaturesEnabled);
+  return /^gemini-3(\.|-|$)/.test(resolved);
+}
+
 /**
  * Checks if the model is a Gemini 2.x model.
  *