Product / UX / UI & API

Proton Lumo

Privacy-first AI assistant from Proton with zero-access encryption, a no-logs policy, and a "ghost mode" that discards chats on close. Runs on open-weight models from Proton's European data centers, excluding third-party providers like OpenAI from inference. Web and mobile clients are open source (GPLv3), though the backend service, routing layer, and model serving are not public. The differentiator is confidentiality - no account is required and conversations are never used for training.

Launched July 2025; Lumo 1.1 added advanced reasoning. Clients are GPLv3 (web client lives in ProtonMail/WebClients; iOS/Android in ProtonLumo), but the service, models, and routing are not open sourced, so the "fully open source" marketing claim is contested.

Openness

2 high confidence

2.0

source: partial(GPLv3 clients only
clients: open(GPLv3 - web in ProtonMail/WebClients, iOS/Android in ProtonLumo)
service: closed(backend, routing, model-serving not public)
license: GPLv3(clients)

Open clients (GPLv3) over a proprietary hosted service: the backend, routing and model-serving layer are not published. Marketed as "fully open source", but support pages and third-party reviews note that only the clients are open. Corrected from 3/open_core on 2026-07-30, and both values were wrong: the ladder has no rung at 3, and a published client standing in for an unpublished engine is source:partial, which it scores 2/source_available. open_core would mean an OSI core with a paid tier withheld.

https://github.com/ProtonLumo/ios-lumo recorded 2026-06-17
iOS client source under GPLv3
https://isitreallyfoss.com/projects/lumo/ recorded 2026-06-17
only the Lumo mobile/web apps are open; service + model interaction code not public

Adoption

3 medium confidence

3.0

Launched July 2025 with Lumo 1.1 following; distributed across Proton's large account base (100M+ Proton accounts) and available on web + iOS + Android with no account required. No Lumo-specific usage numbers disclosed, so reported_traction at a mid level.

https://proton.me/blog/lumo-ai recorded 2026-06-17
Proton's launch announcement for Lumo

Capability

3 medium confidence

3.0

Capable privacy assistant with file upload, web search, and a reasoning mode, but confined to open-weight models and the Proton ecosystem; lighter on multimodal/plugins than frontier consumer apps. Mid-tier on the chat-UI feature matrix.

https://proton.me/blog/lumo-1-1 recorded 2026-06-17
Lumo 1.1 adds faster, advanced reasoning

Unchanged since 2026-07-30 (last edited, not re-checked)