SumizAI vs Lumo by Proton

What Lumo by Proton is

What Lumo is

Lumo is a private AI assistant from Proton, the company behind ProtonMail and ProtonVPN, built around zero-access encryption — Proton encrypts conversations so that even the company itself has no technical way to read them. It's a direct extension of Proton's privacy philosophy from email and VPN into conversations with a language model.

Key features

Messages are encrypted across Proton's entire network, including the company's internal pipeline, until they reach the language model, which itself keeps no logs of conversations — the reply travels back the same encrypted way, so content never crosses a network boundary unencrypted. Models run on servers Proton controls, with no data sent to third-party providers. Lumo's code is fully open source, letting anyone independently verify its privacy claims instead of just taking the company's word for it.

Who it's for

Lumo appeals to people already using the Proton ecosystem (mail, VPN, drive) who value a consistent privacy policy from one provider, and to anyone who treats the content of AI conversations as potentially sensitive and wants assurance it isn't used to train models.

Use cases

In practice, Lumo works well for professional or legal conversations where confidentiality matters, for work at companies with strict GDPR-compliant data protection policies, and as an extension of the rest of the Proton suite for people who already trust the company with their email.

Pricing and business model

Lumo runs on freemium — the free tier has usage limits, and paid plans, including business tiers for teams, unlock higher limits and extra features, consistent with the rest of Proton's subscriptions.

Limitations and what to watch for

Getting the full benefit of Lumo means trusting one company's infrastructure — Proton — so it's worth independently assessing whether its security model (zero-access encryption, European servers, GDPR compliance) meets your requirements.

The Proton ecosystem as a whole

Lumo joins the mail, VPN, cloud storage, and password manager already offered by Proton — for someone already paying for a Proton bundle, adding Lumo to the subscription is a natural extension rather than a decision to trust an entirely new company with sensitive conversations.

Own-run models versus third-party models

Unlike services that broker access to other companies' models, Lumo runs models on servers Proton controls directly — removing an extra link in the chain of trust, where data would otherwise have to pass through a third-party model provider's infrastructure.

Company history as context for trust

Proton has operated in digital privacy for over a decade and has gone through public security audits of its mail and VPN services — that history provides some context for evaluating Lumo's privacy claims, though the product itself is much younger than the rest of the company's portfolio.

Building a ai notes archive without breaking encryption

Because zero-access encryption covers a conversation's transport and storage inside Lumo, not its content once copied out, moving a fragment as a ai notes entry into an external notebook automatically steps outside Proton's protection — worth choosing the destination for that ai notes entry as deliberately as the chat app itself.

AI notes from encrypted conversations

Lumo offers no built-in, lasting notes archive — despite the zero-access encryption protecting a conversation's content, a worthwhile answer someone wants to keep as a ai notes entry still has to be copied by hand into a separate notes app once the chat session ends.

GDPR and FADP compliance as a foundation of trust

The service's European location and GDPR compliance aren't an afterthought — they've been part of Lumo's architecture from the start. For organizations in regulated industries, that's often a hard requirement when choosing an AI tool, not just a nice-to-have.

Open code as a verifiable guarantee

Because Lumo's code is publicly available, independent security researchers can verify whether the actual zero-access encryption implementation matches the marketing claims — a rarity among commercial AI assistants, which usually just ask you to take the provider's word for it.

What's worth checking before choosing

Before choosing Lumo, check the current free-tier limits and whether your organization needs formal confirmation of GDPR compliance beyond what's stated on the product page.

Availability across platforms

Lumo runs as a web app and as native mobile apps for Android and iOS, with the same encryption model on every platform — syncing conversation history between devices happens within that same encrypted Proton infrastructure, with no third-party service in between.

Comparison with competing privacy assistants

While many AI assistants claim to care about privacy only in their privacy policy, Lumo backs those claims with a verifiable, technical zero-access architecture and publicly available source code — the difference between a verbal promise and a mechanism that can be independently checked is what sets Lumo apart from many competing tools advertising "privacy" without technical backing.

Languages and interface localization

Lumo supports an interface in multiple European languages, consistent with the rest of Proton's products aimed at an international user base — a detail that matters for companies employing teams across different EU countries, where one consistent vendor supporting local languages simplifies rollout across an organization without training people in a foreign interface language, which in turn speeds up adoption among staff less comfortable working in English.

Bottom line

Lumo is a private, encrypted AI assistant from Proton, built on the same philosophy as the rest of the company's suite. Anyone who wants worthwhile, confidential answers to land automatically as ai notes in a searchable archive without manual copying should consider a tool built around that workflow.

Comparison with SumizAI

Lumo and SumizAI differ in scope — Lumo is an encrypted chat with no lasting archive, part of the wider Proton ecosystem. SumizAI focuses solely on the notes flow: answers worth keeping automatically become ai notes as Markdown files in a vault you own, with the AI model connected through your own API key to one of seven providers. Anyone who wants encrypted chat as part of the Proton suite will pick Lumo; anyone who wants these notes from AI conversations to build a lasting, searchable archive will find SumizAI the better-fitting tool.

That is our reading of the record. For AlternativeTo's own wording, see its page for Lumo by Proton — the facts above were read on 2026-08-16.

What SumizAI is

A note-taking application built around a conversation with an AI model. You ask a question, the answer streams back, and the answers worth keeping become Markdown notes — filed into a vault that is a folder on your own disk.

A vault is a directory holding base.md, a generated table of contents up to six levels deep, and a notes/ folder with one .md file per note. Before a note is written it is checked against the ones already there, so the fourth note about the same idea gets merged instead of added. Links between notes are ordinary Markdown links to files that exist.

The model is never ours: you bring your own API key to one of seven providers — Anthropic, OpenAI, Gemini, Groq, OpenRouter, a local Ollama or your own server — and pay that provider directly. A question sends the table of contents plus at most five relevant notes within a 24,000-character budget, and the app shows you which five it used.

Every answer kept this way becomes one of these ai notes, ready to search again months later without hunting back through old chats.

Side by side

Where they differ

• Lumo by Proton is a place to have the conversation. SumizAI is not a chatbot — the conversation is the input, not the product. What comes out of it is a .md file with a title, a place in base.md and a duplicate check against the notes already in the vault. If you only want to talk to a model, you do not need SumizAI.
• Lumo by Proton is open source (GPL-3.0), and SumizAI is not. If reading the source is what decides it for you, that is a real argument for Lumo by Proton. The guarantee SumizAI offers instead is structural rather than legal: the notes are Markdown files in a folder you chose, so they open in any editor whether or not the application is running.
• Lumo by Proton is freemium: there is a free tier and a paid one, and the line between them is the thing to read before committing. SumizAI has one plan at a dollar a month, so there is no feature held back for a higher tier — and an unpaid account still opens and exports every vault it already has.
• AlternativeTo's description of Lumo by Proton does not mention Markdown, so check what format your notes end up in before you fill it up. SumizAI writes standard .md files to a folder you picked, and an unpaid account can still export all of them.
• Lumo by Proton advertises encryption. SumizAI answers the same worry a different way: on the desktop the notes never leave your disk, and the material a question sends to the model is capped at the table of contents plus at most five notes — and the app shows you which five it used.
• Lumo by Proton runs in the browser. SumizAI is a desktop and mobile application, and on the desktop the vault is a folder on your own disk rather than a document in someone's cloud.

Which one to pick