Lumo
Proton's AI that promises to never read your conversations.
By Thiago Lourenço Martins
An AI chat that treats your question like a sealed letter
Lumo is the chat assistant from Proton — the same Swiss company behind Proton Mail and Proton VPN, known for taking privacy seriously. It works like any AI chat: you type, it answers, summarizes text, translates, helps draft an email, reviews code. The difference is what happens to the conversation afterward: it's stored with zero-access encryption, meaning not even Proton itself can open what you wrote. It's the difference between a postcard, which any mail carrier can read along the way, and a sealed letter only the recipient can open.
The screenshot that turns into a confidentiality headache
A lawyer pastes a clause from a filing into any AI chat to "just get a quick summary." Someone in finance drops a spreadsheet with client data to "just organize it." Nobody stops to think whether that text becomes training material for another company's model — until someone asks.
That's the number of people at Proton who can open the saved history of your conversations with Lumo, according to the zero-access encryption the company documents publicly. Zero — not even employees.
Five ways to open Lumo without a second thought
Uploads a draft contract or filing as a PDF and asks for the risk points, without that uneasy feeling of not knowing where the text ends up.
Asks about a real employee or client case without typing a single name into a chat that might reuse the conversation to train someone else's AI.
Turns on "Tools" to enable web search and asks something current — without becoming an ad target based on the topic searched.
Asks for an image to illustrate a post or a presentation cover, knowing that idea won't become training material to inspire someone else's image.
Opens the site and just asks — no account, no login. Pure guest mode, for a quick test without leaving a trace.
Is Lumo worth trusting day to day?
rating 3.8 out of 5
I tested it with a fictional service agreement (no real client data) and asked for the risk points — the answer came back organized, in seconds. What tips the scale isn't the model's raw intelligence, which still trails ChatGPT and Claude on complex tasks — it's the privacy architecture, documented in rare technical detail. It's not magic: during processing, Proton's server still sees your message in readable text for a moment to generate the reply, and the company is transparent about that. For anyone handling sensitive information all day, it's still a level of care the competition doesn't offer.
Checked against official sources on July 26, 2026.
In favor
- Chat history protected by zero-access encryption — Proton publicly documents how it works, the same scheme used in Proton Mail and Drive
- You can use it with no account and no card — it opens and you're chatting right away in guest mode
- According to Proton, your conversations are never used to train models, sold, or shared with advertisers
- Covers the basics well: summarizing, translating, editing text, answering questions, generating images, and current-events web search
Where it falls short
- Not full end-to-end encryption: to generate a reply, Proton's server processes your message in readable text for a moment (the company calls it "user-to-Lumo" encryption and explains the difference in detail on its own technical blog)
- Free-plan limits aren't published as numbers — Proton just says "limited" for messages, images, and Max-model usage, without saying how much
- Interface (buttons, menus) was still English-only when checked for this review — only the chat replies come in whatever language you write
- Still a young product (Lumo 2.0 shipped in June 2026): for complex writing or reasoning tasks, ChatGPT and Claude still deliver more polish
From blank screen to first answer, no account needed
- Go to lumo.proton.me
The chat opens straight into the "How can I help?" screen — no login, no card.
- Type your request in the "Ask anything..." box
You can write in Portuguese, English, or Spanish normally; the reply comes back in the same language.
- Want to attach a file?
Click the "+" icon to the left of the text box and pick a PDF or image before you ask.
handy for summarizing a contract, filing, or report - Need up-to-date information?
Click "Tools" and turn on web search before sending your question.
- Send and read the answer
Press Enter or click the send button — the reply appears within seconds, streaming word by word.
- Want to keep the history?
Click "Create a free account" in the top-right corner — without it, the conversation won't be there next time.
A ready-made request to paste in the chat box
Summarize this contract (or legal filing) in up to 6 bullet points, highlighting risk clauses, deadlines, and each party's obligations. Then, in plain language, point out the 3 items that deserve the most attention before I sign or file it. Do not invent any clause that isn't in the text.
Paste the document text before the request, or attach the PDF via the "+" icon. The reply comes back with the 6 bullet points and the 3 attention items separated at the end.
Tips & mistakes from someone who tested it
Do this
- Write in your own language freely — the English is only in the interface, not the conversation
- Use "Projects" to separate chats by case or client — it only shows up once you have a free account
- Turn on "Tools" only when you actually need current data — the reply is faster without it
Avoid
- Assuming it's classic end-to-end encryption — processing briefly passes through the server in readable text
- Uploading a real, sensitive client document before you understand how Lumo works — test with something fictional first
- Expecting saved history without an account — in guest mode, closing the tab makes the conversation disappear
A Portuguese-language tutorial to go further
* Independent pick, chosen for content quality. In Portuguese; we have no relationship or sponsorship with the channel.
How much Lumo costs
Yes, it's free — usable with no card, with or without an account. The paid plan exists for people who hit the free plan's limits and want near-unlimited use.
US$ 0 — no account, no card. Limited access, no history saved between visits.
US$ 0 — limited Max-model usage, limited messages and history, limited image generation, 1 Project.
US$ 12.99/month — more Max-model usage, more messages and history, more images, unlimited Projects and Custom Lumos.
US$ 9.99/month — billed US$ 119.88 every 12 months (23% off the monthly rate), with a 30-day money-back guarantee.
Important detail: Proton charges in US dollars (also accepts euro and Swiss franc, depending on your country) — we don't convert to reais because the value shifts with the exchange rate. Official prices checked in July 2026 (subject to change).
Who Lumo makes sense for
Worth it if you…
- Are a lawyer or any professional handling confidential information (health, finance, HR) and don't want that text becoming AI training data
- Already use Proton Mail or Proton VPN and want to keep everything inside the same privacy ecosystem, with one account
- Want an everyday AI chat — summarizing, translating, editing text — without signing up for one more ad-driven platform
Think twice if you…
- Need the sharpest answer on complex writing, coding, or reasoning tasks — ChatGPT and Claude still lead in that area
- Need to cross-reference dozens of documents at once with page citations — that's a job for NotebookLM, not Lumo
- Work exclusively in Brazilian law and need case law with validated sources — Jus IA was built exactly for that
When another tool serves you better
When the work is 100% legal and you need case law with validated sources, not just a private chat
When you want the most battle-tested model for complex tasks, and extra privacy isn't the priority
When what comes out on screen — the quality of the writing and analysis — matters more than the encryption model behind it
When you need to cross-reference several documents at once, with the exact page cited in every answer
Test it now with any text
Grab any paragraph you wouldn't mind losing — an old email, a news article — and paste it into Lumo with this lesson's prompt. Never start by testing with a real, sensitive client document.
It worked if you get organized bullet points and attention items back, in seconds, without needing to create an account.
What beginners want to know
Is Lumo really free?
Yes. You can open lumo.proton.me and start chatting right away, with no account (guest mode, limited access). Creating a free Proton account gets you more messages and saved history, still with limits — Proton doesn't publish the exact numbers. For near-unlimited use there's the paid Lumo Plus plan.
Do I need a credit card?
No. Not for guest access, not for the free account. A card is only needed if you decide to subscribe to Lumo Plus, which comes with a 30-day money-back guarantee.
Does it work in Portuguese or other languages?
Yes — in testing, Lumo answered in Portuguese without any issue; it responds in whatever language you write in. What's still in English is the interface itself (buttons and menus like "New chat", "Tools"), at least as checked for this review.
Does it work on mobile?
Yes, there are official apps for iPhone (App Store) and Android (Google Play), and it also works directly in your phone's browser.
Is it really more private than ChatGPT?
For stored history, yes: Proton uses zero-access encryption, so not even Proton can open your saved conversations. But the fine print matters: while the model is generating a reply, Proton's server processes your message in readable text for a moment — the company itself calls this "user-to-Lumo" encryption, which is not the same as full end-to-end encryption. Still, it's a stricter privacy model than most competitors, which log conversations and may use them to train AI.
Can I use it without creating an account?
Yes. Just open lumo.proton.me and start typing — the chat works immediately in guest mode. The catch is that without an account you don't keep chat history or organize chats into Projects.
Who makes Lumo?
It's a product from Proton, the Swiss company behind Proton Mail and Proton VPN, known for its privacy focus. Lumo is built on open-source language models and runs on Proton's own European data centers.
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