Lumo

Details

The service provided does not appear to be open source, or source available. The web client and mobile clients are provided under GPLv3 licenses. Source for the service itself, including where it directly interacts with large-language-models, could not be found in our review.

The European Open Source AI Index website came to a similar conclusion, stating:

The only open source code we have found is for the Lumo mobile and web apps. Proton calling the Lumo AI assistant open source based on that is a bit like Microsoft calling Windows open source just because there’s a github repository for Windows Terminal.

On the project’s privacy page they state:

Lumo is powered by open-source large language models (LLMs) […] The models we’re using currently are Nemo, OpenHands 32B, OLMO 2 32B, GPT-OSS 120B, Qwen, Ernie 4.5 VL 28B, Apertus, and Kimi K2. These run exclusively on servers Proton controls so your data is never stored on a third-party platform.

This backs-up the idea that the model handling logic/work is performed server-side, and not in the FOSS client applications. It should also be noted that they call the models used “open-source” which many would consider incorrect, with open-weights being the more appropriate term since not all of those models can be reproduced and modified from source.

The project is openly advertised as open source. For example, their about page states:

Unlike other AI assistants, my code is fully open source, so anyone can verify that it’s private and secure — and that we never use your data to train the model.

When the project was initially announced, the above quoted statement was used but even the client code was not made available at that time. This was reportedly queried by a Privacy Guides user, with Proton apparently stating that this “reflects our long-term intention and the values we stand for, not necessarily the instantaneous state upon launch.”.

Proton services are operated by Proton AG, a Swiss corporation whose primary shareholder is the non-profit Proton Foundation.

The project appears to funded from donations, grants, merchandise and from its paid hosted services.