Gemini 4 Hydrogen Is Now the Default Model in Google AI Mode

Google made Gemini 4 Hydrogen the default model in AI Mode on November 12, and it now answers the hardest AI Overview questions too, according to a post on X from Google’s Robby Stein.

So the AI answers your pages show up in now come from Gemini 4 Hydrogen in AI Mode. Google calls it the biggest model upgrade to Search yet.

It landed two days into the November core update. Bad timing for your reports.

What changes in Search

Google’s Search announcement lists four changes for everyone who uses AI Mode:

• Your long, multi-part questions, typos and all, get an answer for each part.
• A stronger query fan-out, so Search runs more sub-searches at once and links to a wider range of sites.
• More images, comparison tables, structured answers and custom tools in the answers your visitors read.
• Better answers in every language AI Mode supports.

Stein, who runs product for Google Search, said Gemini 4 Hydrogen is “now the new default model in AI Mode”, The Verge reports.

But what counts as the hardest AI Overview questions? Google hasn’t said. And neither Google nor Stein gave a number for the extra links, Search Engine Journal notes.

Paying for Google AI Ultra? You can still pick Gemini 4 Carbon from the + menu.

It has daily limits, which Google’s AI Mode help page says can change with demand and your plan.

What the model is

Gemini 4 Hydrogen is the fast, cheaper model in the Gemini 4 family. Speed is the point.

Google built it for everyday coding and agent work, and leaves deep thinking to the frontier models, Carbon and Argon.

In Google’s model post, Gemini 4 Hydrogen scores 51 on the Artificial Analysis Intelligence Index against Argon’s 50. Google says it finishes tasks 2.5 times faster than Gemini 3.8 Flash.

Those are Google’s own numbers, though. You’ll find Gemini 4 Hydrogen in AI Mode, the Gemini app, the API, AI Studio and Sheets.

What we checked

On 13 November we read Google’s Gemini API pricing page. Gemini 4 Hydrogen costs $1.50 per million input tokens and $7.50 per million output, twice what Gemini 3.8 Flash costs you today.

• Gemini 3.8 Flash costs you the same as Gemini 4 Hydrogen from January 1. Gemini 4 Hydrogen has a free tier, and caching is automatic only.
• The Gemini 4 Hydrogen model card gives a March 2026 knowledge cutoff.
• Google’s Search Status Dashboard still showed the November core update as active, nearly three days in.

Why it matters

Do you track AI citations or AI Mode clicks? Then write down two dates.

November 10 for the start of the November core update. November 12 for Gemini 4 Hydrogen in AI Mode.

Compare clicks, citations and referrals from AI Mode before and after each date, or you’ll blame the wrong change when traffic moves and fix pages that were never the problem.

My read: the fan-out change matters more to you than any benchmark Google quoted, because it decides how many different sites can get pulled into a single answer.

So one narrow part of a question, answered well, can earn a link.

Still, more tables and custom tools inside the answer give people fewer reasons to click through to your site, and a wider range of sites is a claim until you see it in your own numbers.

So watch your inline links in AI Mode and your referrals from AI Mode. Weekly is fine.

Then there’s your reporting, which won’t make this easy:

• Search Console’s Generative AI report shows impressions only, and it won’t tell you which model answered.
• Gemini’s cited links seem to have lost their UTM tags, so some of your visits from Gemini land in Direct.

Meanwhile, if you build on the Gemini API, test Gemini 4 Hydrogen against your Gemini 3.8 Flash calls while Flash is still the cheaper of the two. The gap closes on January 1.

New to AI answers? Start with our guide to AI search and your website.

It’s short.

Common Questions

Is Gemini 4 Hydrogen the default model in Google AI Mode for everyone?

Yes. Google’s Robby Stein said on November 12, 2026 that Gemini 4 Hydrogen is the new default model in AI Mode, and Google says it’s available in Search for all users globally.

Does Gemini 4 Hydrogen power Google AI Overviews too?

Partly. Robby Stein said Gemini 4 Hydrogen is used for the hardest questions in AI Overviews, but Google hasn’t said which questions count as hardest or which model answers the rest.

How much does the Gemini 4 Hydrogen API cost?

$1.50 per million input tokens and $7.50 per million output tokens on the paid tier, with a free tier in Google AI Studio. Gemini 3.8 Flash costs half that until December 31, 2026.