Lumo

What Is Lumo?

Proton makes a claim that no major US AI company can match: not even Proton itself can read your conversations. That is not marketing copy. It is a mathematical guarantee backed by zero-access encryption — the same architecture Proton has used for Proton Mail since 2013, now applied to AI chat.

Lumo is Proton's AI assistant, launched in July 2025 and reaching 10 million users by June 2026. It is built on open-source language models, hosted on Proton's European infrastructure in Geneva, Switzerland, and encrypted client-side before any data reaches Proton's servers. When you close a conversation, the content is unreadable to everyone except you. No model training. No server-side logs. No exceptions under Proton's control.

Proton AG is the Geneva-based company behind Proton Mail, Proton VPN, Proton Drive, and Proton Pass. The company launched Lumo as the AI product its existing 100 million-plus user base was asking for — private AI, not AI that happens to have a privacy policy. The company is owned by the nonprofit Proton Foundation and has operated on European infrastructure since its founding. Lumo 2.0, released on 30 June 2026, added image generation and recognition, advanced reasoning modes, user-controlled memory, and Projects workspaces, closing the feature gap with mainstream competitors.

Key Features

Zero-Access Encryption

Every conversation in Lumo is encrypted on your device before it leaves for Proton's servers. The encryption keys stay with you. Proton's infrastructure receives and stores only ciphertext it cannot decode. This is the same model that made Proton Mail the world's largest encrypted email provider — now applied to AI.

The practical consequence: if a government requests your conversation history from Proton, Proton has nothing readable to hand over. If Proton's servers were compromised, attackers would find encrypted blobs with no useful content. Against ChatGPT's approach — where OpenAI retains conversations for up to 30 days by default and can use them for training — this is a structurally different privacy architecture, not a slightly better policy.

Open-Source Codebase and Models

Lumo's code is fully open source and auditable on GitHub. The language models powering it are open-source models rather than proprietary systems, which means independent researchers can inspect both the application layer and the underlying AI. For organisations that need to verify security claims — rather than trust them — this matters enormously. Proton has a track record of publishing security audits and allowing independent verification of its encryption implementations.

The open-source architecture also provides resilience against vendor lock-in concerns. Proton cannot subtly change what models process your data in ways that would go undetected.

Lumo 2.0 Feature Set

The June 2026 Lumo 2.0 release significantly expanded capability beyond basic chat. Image generation and recognition are now fully integrated — users can generate images from text prompts, recognise objects and scenes in uploaded photos, and convert sketches to images. The Advanced Thinking mode applies deeper reasoning chains to complex questions in mathematics, logic, and research synthesis.

A user-controlled memory system stores facts you choose to share (preferences, context, ongoing projects) and applies them across sessions. This is opt-in and transparent — Lumo does not decide unilaterally what to remember. Projects workspaces organise related conversations and linked Proton Drive files, functioning like persistent work contexts for ongoing tasks.

Performance in Lumo 2.0 is 127% higher on benchmark scores for the Lite model and 240% higher for the Max model compared to the original Lumo launch, with response times up to 76% faster.

Proton Ecosystem Integration

Lumo connects directly to Proton Drive for document context, enabling users to reference files in their encrypted storage without uploading them to a separate service. The broader Proton suite — Mail, VPN, Pass, Calendar — shares authentication, so existing Proton subscribers have immediate access. For users already inside the Proton ecosystem, Lumo is a natural extension rather than a new service to evaluate.

The Tor integration for anonymous access is unusual among AI assistants. Users who want to interact with Lumo without any IP tracing can do so via Tor browser, which Proton explicitly supports — a niche but meaningful option for journalists, activists, and high-risk users.

Custom Lumos

Lumo Plus subscribers can create Custom Lumos: AI assistants pre-configured with specific instructions, personas, and knowledge contexts. A research analyst might build a Lumo primed with specific frameworks. A legal professional might create one instructed to apply a jurisdiction-specific lens. These configurations persist across sessions and behave like purpose-built assistants, reducing the prompt engineering overhead for recurring tasks.

Pricing

Lumo's free tier is genuinely usable: limited AI chat with zero-access encryption, one project workspace, limited image generations, and web search with citations. The encryption and privacy guarantees apply identically to free users — Proton does not tier privacy by subscription level.

Lumo Plus at $12.99/month (or $120/year, equivalent to $10/month) adds unlimited chats, expanded chat history, advanced image generation and recognition, priority access to the fastest and most capable models, unlimited projects, unlimited Custom Lumos, and a 30-day money-back guarantee. At $12.99/month, Lumo Plus sits roughly 15% below Mistral's Le Chat Pro (€14/month at current EUR/USD rates) and 35% below ChatGPT Plus ($20/month).

The question for potential subscribers is whether the privacy guarantee justifies the premium over Le Chat Pro. For users who would otherwise use ChatGPT or Claude — services that retain conversations by default — switching to Lumo Plus actually represents a cost saving alongside a privacy improvement. For users comparing Lumo Plus to Le Chat Pro, the decision turns on whether verified zero-access encryption is worth €3–4/month extra.

A Lumo Professional tier for teams is available at custom pricing, with admin controls and secure collaboration features. Specific pricing requires contacting Proton directly.

EU Compliance & Privacy

Lumo operates under Swiss law — specifically the Federal Act on Data Protection (FADP), which Switzerland revised in September 2023 to align with GDPR standards. The FADP covers the same core principles as GDPR: lawfulness of processing, data minimisation, purpose limitation, data subject rights, and breach notification. The Swiss Federal Data Protection and Information Commissioner (FDPIC) enforces it.

The key nuance: Switzerland is not an EU member state. EU GDPR does not apply directly to Proton AG. For most users, this distinction is immaterial — Swiss FADP provides equivalent protection and Switzerland has an EU adequacy decision for data transfers. For organisations with legal clauses requiring EU-jurisdiction data processing specifically (some German and French public-sector contracts, for example), this warrants a legal review.

Where Lumo goes beyond GDPR compliance is in the technical architecture. Zero-access encryption is not a compliance tick-box — it makes compliance disputes moot for conversation content. No server-side logs means no data to subject to access requests or law enforcement orders. Open-source code means the encryption implementation can be independently verified rather than taken on trust. For journalists, lawyers, healthcare providers, and human rights workers, this architecture is meaningfully safer than policy-based privacy guarantees.

Who It's Best For

Privacy-first individuals and professionals who need AI assistance but are not willing to trade conversation privacy for capability. Journalists, lawyers, healthcare workers, and activists who handle sensitive information daily are the clearest use case.

Existing Proton users who want AI integrated into an ecosystem they already trust. The native Proton Drive integration and shared authentication make Lumo a low-friction addition for Proton Mail or Proton VPN subscribers.

Organisations in regulated sectors that need verifiable privacy claims rather than policy promises. Lumo's open-source architecture and zero-access encryption provide the independent verification that a privacy policy cannot.

If you need frontier model performance matching GPT-4o or Claude Sonnet for complex reasoning tasks, Lumo's open-source models currently fall short. If you need an extensive third-party integration ecosystem or a developer API, Lumo does not offer either — it is a Proton-ecosystem product, not a platform.

The Verdict

Lumo solves a real problem that no US AI assistant can solve: private AI where the service provider genuinely cannot access your conversations. The zero-access encryption architecture is technically sound, independently verifiable, and backed by Proton's decade-long track record in privacy infrastructure. Lumo 2.0 closed enough of the capability gap to make it a credible daily driver for most users. The weak points are real — frontier model performance still trails Anthropic and OpenAI, and the integration ecosystem is limited to the Proton suite. For users who prioritise privacy and are already in the European software ecosystem, Lumo is the only AI assistant that earns an unqualified recommendation on both dimensions.

Frequently Asked Questions

Is Lumo GDPR compliant?

Lumo operates under Swiss law (Federal Act on Data Protection — FADP), which is widely considered equivalent to GDPR. Switzerland is not an EU member state, so EU GDPR does not apply directly. For most purposes the distinction is immaterial; organisations requiring explicit EU data residency should verify Swiss FADP adequacy status with their compliance team. Lumo does not log conversations server-side and applies zero-access encryption to all stored chats.

Can Proton read my Lumo conversations?

No. Lumo uses zero-access encryption, meaning conversations are encrypted client-side before reaching Proton's servers. Proton does not hold decryption keys and cannot read your chats. Any conversations you save are stored in a format only decryptable on your own device. This has been independently verified through Proton's open-source codebase.

How does Lumo compare to ChatGPT?

Lumo's core advantage over ChatGPT is verifiable privacy: zero-access encryption and no server-side logging, versus ChatGPT conversations that OpenAI retains by default and may use for training. ChatGPT has a larger plugin ecosystem, stronger frontier model performance, and more enterprise integrations. At $12.99/month versus $20/month, Lumo Plus is also cheaper. Lumo wins on privacy architecture and price; ChatGPT wins on raw capability and ecosystem breadth.

What is the difference between Lumo Free and Lumo Plus?

Lumo Free includes limited AI chat with full zero-access encryption, one project workspace, limited image generations, and web search. Lumo Plus at $12.99/month adds unlimited chats, expanded history, advanced image generation and recognition, priority access to the fastest models, unlimited projects, and unlimited Custom Lumos. Both tiers apply identical zero-access encryption — privacy is not gated by subscription.

Where is Lumo data stored, and is it in the EU?

Lumo data is stored on Proton's European infrastructure in Switzerland. Switzerland is not an EU member state, so data falls under Swiss FADP rather than EU GDPR directly. For most privacy purposes this distinction is immaterial — Switzerland holds a GDPR adequacy decision. Organisations with explicit EU-jurisdiction data residency clauses should seek legal review.