Gemini 4 Hydrogen becomes the default model in Google’s AI Mode

Google says Hydrogen copes better with very specific requests, hard-to-read typos and questions in several parts. It splits a question into sub-topics and searches all of them at once, which Google says links to a broader range of sites. Answers also carry more visuals, with maps, graphs, comparison tables and images among them, The Verge notes. Search Engine Journal found no figure for how many more links or sites appear, in Google’s post or in Stein’s thread. The model also reached the Gemini API, AI Studio and the Gemini app the same day. In the API, Google prices it at $1.50 per million input tokens and $7.50 per million output tokens (tokens are the word fragments a model reads and writes), flat across its full 1-million-token window.

SEJ also flags the timing. Google’s November core update, a broad change to how Search ranks sites, began on 10 November and was still rolling out on the afternoon of the switch.

Paying Google AI Pro and Ultra subscribers also get Hydrogen in Google Antigravity, Google’s coding tool. On our price sheet, checked 12 November, Google AI Plus costs $4.99 a month, AI Pro $19.99 and Ultra $99.99.

Since the core update began on 10 November and AI Mode’s model changed on 12 November, a site’s AI Mode citations measured across this week mix two changes, and a shift can be pinned on either one only if both dates are logged.