How many sources can NotebookLM hold?

In more detail

The per-notebook source limit is the constraint most research projects hit first. Google currently documents 50 sources per notebook on the standard service and 100 notebooks per account, with a per-source ceiling of 500,000 words or 200 MB. Paid Google plans raise the source ceiling, but Google has repackaged these tiers more than once and availability differs by region, so confirm the current number on Google's Gemini Notebook help page. If you are working past the limit, the practical answers are to split a project across several notebooks by theme and to curate tightly — a focused source set usually produces better answers than an exhaustive one.