Google is testing a new “Lecture” mode for its AI-powered research assistant, NotebookLM, as part of an expansion of its Audio Overviews feature aimed at deeper, long-form learning.
According to details spotted by TestingCatalog during an app teardown, the new Lecture format differs markedly from existing Audio Overview styles such as “Deep Dive” and “Debate”. Instead of a conversation between two AI-generated hosts, the Lecture mode uses a single narrator to deliver a continuous and structured explanation of a topic.
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When combined with the app’s “Long” duration setting, the Lecture mode can produce audio sessions lasting up to 30 minutes. The format is designed to connect ideas across multiple user-provided sources, offering a more cohesive and scholarly narrative rather than a brief summary or simulated discussion.
The moment you’ve ACTUALLY been waiting for… Introducing Deep Research!
Rolling out now, Deep Research browses hundreds of sites to craft an organized report AND gives you an annotated list of sources for deeper exploration, all of which you can add directly to your notebook. pic.twitter.com/RK5RCXcOlk
— NotebookLM (@NotebookLM) November 13, 2025
The tone of the Lecture format is described as calm and explanatory, making it suitable for extended listening. This approach is intended to benefit students, researchers and professionals who want to absorb complex material during activities such as commuting or exercising, without needing to read from a screen.
TestingCatalog has reportedly generated a full 30-minute lecture using the feature, indicating that the format is likely a planned addition to NotebookLM rather than a limited internal experiment. If launched, it would become the fifth Audio Overview mode available in the app.
Alongside the Lecture format, Google is also preparing to introduce British English narration voices in 2026. The company hinted at the update on X, formerly Twitter, using the phrase “you’ll be absolutely chuffed”.
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A preview of the British voice technology is already available through a Featured Notebook titled “Archive 1945”, developed in collaboration with The Economist. While the Lecture mode remains in testing and has no confirmed release timeline, the presence of working demonstrations suggests Google is actively preparing the feature for wider use.