NotebookLM vs Perplexity Spaces vs Claude Projects

All three will take your files. Only one of them promises to stay inside them.

That one is NotebookLM, which Google renamed Gemini Notebook in July and which most people still call NotebookLM. Perplexity Spaces and Claude Projects both let you build a folder of sources and ask questions against it, and on a vendor's feature page the three look interchangeable. In use they are not. The biggest disagreement is over where an answer is allowed to come from. The one that bites later is what happens once your pile of documents outgrows what the model can read at once.

We already compared NotebookLM and Perplexity on the question of what happens to a web source after you add it. This page is narrower. Picture the job a contracts lead actually has: a 140-page master services agreement, four amendments, a vendor's SOC 2 summary and thirty pages of negotiation notes, plus a boss who wants to know which amendment moved the liability cap. That is the test bed for everything below. The vendor limits are as of October 2026, and the behavior comes from each product's documentation and how it is built to answer.

The short answer

Limits come from each vendor's help center as of October 2026. Perplexity's own pages disagree on the per-file cap (25 MB for Spaces, 40 MB for uploads generally), so plan around the smaller number.

Citation accuracy

NotebookLM wins this, and the margin is wide.

Every claim in a NotebookLM answer carries a numbered marker, and clicking it opens the source scrolled to the exact paragraph. Ask which amendment changed the liability cap and you can check the answer in one click, against the clause itself. Ask about a data-residency clause that appears in none of the documents and it is built to say the sources do not cover it, because it has nowhere else to look. That refusal is worth more than any feature on the other two products.

Perplexity Spaces cites at the file level. You see "MSA_final.pdf" as source 2, and then you go find the clause yourself. With web search on, which is the default, an indemnification question can pull in a law firm's blog post about indemnification in general and cite it in the same style as your contract, right next to it. Read fast and you will not notice which sentence came from which.

Claude Projects is the odd one. It is the strongest reasoner of the three, and while the documents fit in its context it reads all of them at once, which is what you need to notice that two amendments set different notice periods. But it will happily answer without citing anything, and when it searches project files it names a file rather than a passage. Claude's general knowledge also sits underneath your documents. Ask it what "consequential damages" usually excludes and it will tell you, fluently, whether or not your contract says so.

Source grounding, and how to tighten it

You can close most of the gap with settings, and almost nobody does.

In Perplexity, turn web search off for the Space. Answers then come only from uploaded files, and the blog-post problem goes away. Leave it on for Spaces whose job is current research, like tracking a competitor's pricing.

In Claude Projects there is no switch. The fix is the project's custom instructions, and the one I would use reads: "Answer only from project files. Quote the clause and name the file and section for every claim. If the files do not cover it, say so." A verbatim quote is fast to check with a text search. An instruction is still not a boundary, though, and the place to watch is definitions, where Claude's training is strongest and most tempting to lean on.

NotebookLM needs nothing. That is the point of it.

Context limits: where each one runs out

This is the part vendors describe least clearly.

NotebookLM counts sources. Fifty on the free plan gets tight fast if the negotiation notes arrive as forty separate emails, and the fix is to merge them into one PDF, which is allowed as long as a file stays under 500,000 words.

Perplexity counts files too, around 50 per Space on Pro. The per-file cap is the one to plan for: a scanned 140-page agreement at a resolution you can actually read can run past 25 MB and needs compressing first. And because it answers from retrieved chunks, check any answer that should draw on two documents. Make sure both are cited.

Claude Projects counts tokens, and the behavior changes partway through. Project knowledge is loaded straight into Claude's 200,000-token context window while it fits, which is roughly 500 pages of plain prose. Past that, Anthropic switches the project to retrieval (RAG) mode and says capacity grows by up to ten times. Users have reported the switch happening much earlier than the docs imply, around a dozen files, and the interface does announce it with a line about looking up "specific information as needed." The difference matters. In full-context mode Claude reads everything and catches contradictions across documents; in RAG mode it reads what its search pulled back, and it behaves more like the other two. A contract set like the one above sits close to the edge, and adding one scanned report can tip it over without you noticing anything except a quieter, worse answer.

Which one to use

Use NotebookLM when someone will check your work against the documents. Legal review, compliance, anything that ends in "show me where it says that." The free plan is enough to find out.

Use Perplexity Spaces when your files are half the story and the other half is on today's web, and switch web search off in any Space where that is not true.

Use Claude Projects when you need the documents thought about, rather than just retrieved from: drafting a response memo, finding where two amendments collide, turning thirty pages of notes into a negotiation position. Keep the project small enough to stay out of RAG mode, write a strict instruction about citing, and verify every clause it quotes. If you are deciding between assistants more broadly, our Claude vs ChatGPT vs Gemini comparison covers the rest of what Claude is good and bad at.

The setup I would recommend to that contracts lead: NotebookLM holds the full contract set and answers every "where does it say" question. Claude gets a copy of the same files, trimmed to the documents that matter for the task at hand, and does the thinking. Perplexity stays outside both, for checking anything that might have changed since the PDF was saved. For a wider set of research tools, including Elicit and Consensus, see our AI research tools roundup.

Frequently Asked Questions

Which is most accurate at citing sources: NotebookLM, Perplexity Spaces or Claude Projects?

NotebookLM. It answers only from your sources and links each claim to the exact passage. Perplexity Spaces cites at the file or web page level, and Claude Projects often answers without a citation unless you instruct it to quote and name the file.

Can Perplexity Spaces answer only from uploaded files?

Yes. Turn web search off for the Space and answers come only from the files you uploaded. With web search on, which is the default, Perplexity mixes web results with your files in the same answer.

What is the Claude Projects knowledge limit?

Project knowledge loads directly into Claude's 200,000-token context window while it fits. Beyond that, Claude switches the project to retrieval (RAG) mode, which Anthropic says expands capacity by up to 10 times. Individual files can be up to 30 MB.

How many sources can NotebookLM hold in 2026?

The free plan allows 50 sources per notebook, Google AI Pro allows 300, and Google AI Ultra allows up to 600. Each file can be up to 500,000 words or 200 MB.