Proton integrates the Swiss language model Apertus into its AI assistant Lumo

Proton and the research team behind Apertus, the fully open language model developed by EPFL, ETH Zurich and partner institutions, are partnering to advance open and sovereign AI in Switzerland and Europe.

Proton, the Geneva-based technology company specializing in privacy-focused services, is integrating Apertus 1.5 into its AI assistant Lumo, making the model available as an option to tens of millions of users. As part of the partnership, Proton will share user feedback with the Apertus research team to help improve the model.

Apertus was created by researchers at EPFL and ETH Zurich together with partner institutions, and was launched in September 2025 as a fully open multilingual model. Trained on the Alps supercomputer at the Swiss National Supercomputing Centre (CSCS) and released under the Apache 2.0 open-source license, it documents its training data, source code and development process transparently, allowing researchers, public institutions and companies to inspect, adapt and further develop it. The model was trained on publicly available data, respects website opt-outs, including retroactively, and is designed to remove personal data from its training data at scale.

Feedback from real-world use

Feedback from millions of users is one of the main resources leading AI companies draw on to improve their models, while open models developed in academic settings rarely benefit from comparable input. Through the integration into Lumo, the Apertus team will for the first time gain access to voluntary feedback from real-world deployment, provided by users who have given their informed consent.

As with all conversations in Lumo, chats with Apertus 1.5 are protected by zero-access encryption and remain private. Users can actively choose to submit anonymized feedback on the model’s responses, which can then be shared with the research team to support its further development.

Since its launch, Apertus has increasingly moved from research into practical deployment. Organizations that have deployed Apertus 1.5 or integrated it into their offerings include Swisscom, Infomaniak, OnPrem.ai, Stepping Stone, Safe Swiss Cloud, Mono.chat, Helvetra, Featherless.ai, Public AI and AI Potluck.