Fullstack Applied AI Engineer; Lumo

Join Proton and build a better internet where privacy is the default

At Proton, we believe that privacy is a fundamental human right and the cornerstone of democracy. Since our inception in 2014, founded by a team of scientists from CERN, we have dedicated ourselves to providing free and open-source technology to millions worldwide, ensuring access to privacy, security, and freedom online.

Our journey began with Proton Mail, the largest secure email service globally, and has since expanded to include Proton VPN, Proton Calendar, Proton Drive, and Proton Pass. These tools empower individuals and organizations to take control of their personal data, break away from Big Tech’s invasive practices, and defeat censorship. Our work impacts hundreds of millions of lives, from activists on the front lines defending freedom to leaders in governments protecting sensitive information.

In some cases, Proton’s services have even been instrumental in saving lives by enabling secure and private communications in high-risk situations.

Proton is a profitable company that does not rely upon VC funding, supporting over 100 million user accounts with a growing team of over 500 people from over 50 different countries, from the world's top companies and universities. We value intelligence, learning potential, and ambition in our hiring process. Adaptability is key as we navigate uncharted territories and redefine how business is conducted online.

Hiring at Proton is highly selective, with less than 1% of candidates hired. We believe smaller teams of exceptional talent will always prevail over larger teams with lower talent density. You will have the opportunity work with many of the world's top minds in their fields, ranging from former international math and science olympiad winners to chess champions.

We have a global mindset and big ambitions but remain a start‑up  value empowerment and flexibility and keep our structure flat to keep moving fast and avoid unnecessary politics. Tired of blending into the crowd? Join us and do work you can truly be proud of. Check our open‑source projects!

Lumo is Proton's privacy‑first AI assistant that fundamentally reimagines how AI should work - empowering users without exploiting their data. Unlike traditional AI platforms that harvest user conversations for training and profit, Lumo operates with zero‑access encryption, keeps no server‑side logs, and ensures that conversations remain completely confidential.

Built by the team behind Proton Mail, Proton VPN, and backed by the nonprofit Proton Foundation, Lumo represents a paradigm shift in AI development. We believe the benefits of AI are too great to miss, but the privacy risks of current implementations are too serious to ignore. Lumo is based on open‑source language models, operates from Proton's European datacenters, and provides unprecedented transparency in the AI space.

To deliver the full power of artificial intelligence while maintaining user privacy as an uncompromising core principle. We're building an AI that only works for you, not the other way around - where your conversations remain confidential and your data stays fully under your control, never shared, sold, or stolen.

Lumo implements multiple layers of encryption throughout the entire pipeline, from device‑to‑server communication through to long‑term storage, creating a privacy architecture that's simply much stronger than anything else on the market. The platform runs on open‑source models including Mistral's Nemo and Nvidia's Open Hands 32B, with full source code transparency.

We are seeking a Fullstack Applied AI Engineer to build and maintain the complete AI infrastructure powering Lumo's privacy‑first platform. You'll own the full stack from database to frontend, implementing AI tool calling systems, privacy‑preserving search, and encrypted services while ensuring 99.9% uptime for millions of users.

This role combines AI/ML engineering, backend development, site reliability, and frontend integration using Rust, PHP, and modern web technologies to deliver scalable, encrypted AI experiences.