Megan Ellis / Android Authority
TL;DR NotebookLM has removed its biggest bottleneck, boosting custom chat prompts from 500 to 10,000 characters.
Users can now define detailed personas, tones, rules, and context without fighting the character limit.
For anyone who’s been using NotebookLM to digest massive PDFs or brainstorm via the Audio Overview feature, you probably ran into a big limitation: the chat customization field. Until now, if you wanted to tell Google’s research tool how to talk to you, you were boxed into a meager 500 characters.
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That changes now. Google has expanded the limit to a massive 10,000 characters, 20 times the previous limit. Now you have plenty of space to set tone, context, goals, constraints, and personality without butchering your instructions. The NotebookLM team confirmed the update on X.
This update affects the “Configure notebook” settings in the chat interface, where you set the AI’s goal, style, and role. In late October 2025, Google polished the underlying engine to improve context understanding, but that power was often bottlenecked by the short instruction leash. With this restriction lifted, the model’s improved reasoning capabilities can actually stretch their legs.
This change lands on the heels of a major upgrade cycle NotebookLM has been pushing through over the past months. The service recently improved how long conversations are retained, how much context the model can handle, and how coherent responses remain over time.
Those improvements already laid a stronger foundation, but the 10,000-character limit seems like the missing piece. Before, Custom mode was too limited for anyone working on long projects. If you wanted to build a steady editorial assistant, set rules for a research partner, or create a writing companion with a unique voice, there just wasn’t enough space.
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