What AI model does it use?

What AI model does NotebookLM use?

Search for NotebookLM in September 2026 and you'll land on something with a different name. Google renamed it Gemini Notebook on July 16, and Josh Woodward, who runs Google Labs and the Gemini app, wrote that it "remains a standalone product focused on being your premier research tool, but it will now do more across the Google ecosystem." The model question has a clear answer from a month before that.

Gemini 3.5 plus Antigravity, since June 8

On June 8, 2026, Trond Wuellner, who leads product for NotebookLM, announced: "we're upgrading NotebookLM to run on Gemini 3.5 and Antigravity." Antigravity is Google's agent system (the name is shared with its coding tool for developers). The same post says each notebook "is now equipped with a secure cloud computer", so NotebookLM can write and run code on your sources.

Google measured the upgrade against its previous setup. It reported an average win rate of "over 65%" across its top five evaluation areas, with 69.9% on large document analysis and 78.2% on web research and finding sources. Those are Google's own side-by-side tests (a win rate here being how often the new system's answer was preferred), so read them as Google's claim.

Gemini 3.1 Pro, for paid plans only

There's a second model for subscribers. When Google released Gemini 3.1 Pro on February 19, 2026, it added that "3.1 Pro is also now available on NotebookLM exclusively for Pro and Ultra users." So Google AI Pro and Ultra subscribers have a Pro-tier model available that free users don't.

Why "Gemini 3.5" isn't a full answer

Gemini 3.5 is a family, with Flash and Flash-Lite versions among others, and Google's post doesn't say which one NotebookLM uses. The help center is vaguer still; it promises "Gemini's advanced reasoning" with no number at all.

It's also been a busy summer for Gemini. Google has shipped newer Flash models since June, up to 3.8 Flash on September 2, which went into the Gemini app and AI Mode in Search for paying subscribers. I found no post moving NotebookLM to any of them, so 3.5 is the last model Google has named for it. That gap is exactly what this page's monthly source check is there to catch.

Still unanswered

Which Gemini 3.5 variant is the default, whether free and paid users share it, and which models make Audio Overviews (the podcast-style summaries NotebookLM became known for) and the other generated formats.