Google brings Gemini 4 Hydrogen to Search, makes it the default in AI Mode

Google is bringing Gemini 4 Hydrogen to Search, which it describes as the biggest model upgrade to Search yet. Google announced this on its blog. The model is now available globally to all users.

Robby Stein also posted about it on X, wrote: “The biggest model upgrade to Search yet has landed. Gemini 4 Hydrogen is here and brings cutting-edge intelligence to all Search users. It’s now the new default model in AI Mode & being used for your hardest questions in AI Overviews.”

Here is how it looks.

Google listed several improvements in its blog post:

• Better understanding of intent: Search can handle more nuanced and complicated questions, including questions with multiple parts, hard-to-understand typos, or highly specific requests. With deeper instruction following and tool calling, Search follows what you want more precisely and addresses each part of your question.
• Improved query fan-out and linking: Hydrogen’s advanced reasoning improves Google’s query fan-out technique, connecting users to a broader range of helpful links. By understanding the question more thoroughly and running simultaneous queries across all the relevant subtopics, Search can help users find sites they might not have discovered before.
• More visual responses: Responses are more adaptive, visual, and easy to scan, with more images, structured responses, comparison tables, and custom tools.
• Richer language understanding: Responses should be more nuanced and helpful across all supported AI Mode languages.

For site owners and publishers, the improved query fan-out and linking is particularly interesting. Google says the model connects users to a broader range of helpful links. However, it is too early to know how this change will affect organic clicks and website traffic.