Google makes Gemini 4 Hydrogen the default model in AI Mode worldwide
Google has made Gemini 4 Hydrogen the default model in AI Mode for every user worldwide, starting today. Robby Stein, VP of Product for Google Search, said on X that Hydrogen is also handling "your hardest questions in AI Overviews", and Google's Search post confirms the model is live globally for all users.
Hydrogen is built for speed and efficiency, unlike Gemini 4 Carbon and Argon, which Google designed for longer-running deep thinking. Carbon went out to AI Mode for Ultra subscribers on Nov. 10, and Argon arrived as a paid option on Oct. 13. Google says Hydrogen copes better with multi-part questions, typos, highly specific queries and follow-up commands, and improves query fan-out, the process of running several searches at once across an inquiry's subtopics. Google claims this connects users to a wider range of helpful links, including sites they might never have found, though it gave no figures for links or sites.
The switch landed two days into the November core update, which began Nov. 10 and was still rolling out. For anyone tracking how often AI Mode or AI Overviews cite their site, this month's data now spans a model change on Nov. 12 as well as the update, so logging both dates separately lets you compare before and after each one rather than treating November as a single event. Google has not said which AI Overview questions count as the hardest, so it is worth watching for that detail to judge how much of your tracking reflects the change.
Reported by Search Engine Journal ↗
Topics: AI Mode, AI Overviews, Google Search