Google Makes Gemini 4 Hydrogen the Default Model in AI Mode Worldwide

Google has switched AI Mode to Gemini 4 Hydrogen as the default model in every market. The company is also using the same model for the most difficult questions that trigger AI Overviews.

Why it matters: Search marketers tracking AI visibility should expect changes in how AI Mode and AI Overviews answer and cite sources, so they should re-check visibility and citation performance on complex queries.