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 at heart. We 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 here!

About Lumo

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.

Our Mission: 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.

Our Technology: 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 OpenHands 32B, with full source code transparency.

Role Summary

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.

What You Will Do

AI Systems Development

• Build and maintain AI tool calling frameworks that enable secure integrations with external services
• Implement a privacy-preserving search infrastructure that doesn't expose user queries
• Develop AI model serving pipelines with encrypted data processing throughout
• Create intelligent query routing and result filtering systems optimized for AI consumption
• Build real-time AI conversation APIs that maintain zero-access encryption

Fullstack Infrastructure

• Design high-performance backend services in Rust for AI processing and PHP for web integration
• Build responsive web interfaces and admin dashboards using modern JavaScript frameworks
• Improve our microservice architecture with service mesh for scalable AI platform development
• Improve our automated deployment pipelines and infrastructure-as-code for reliable operations
• Develop monitoring and observability systems that preserve user privacy

Site Reliability & Operations

• Maintain highly available AI services with automated monitoring, alerting, and incident response
• Implement chaos engineering and performance testing for encrypted AI workloads
• Build auto-scaling systems for cost-effective GPU utilization and global traffic handling
• Conduct capacity planning and optimize system performance for millions of users

Core Technical Requirements

• 5+ years fullstack development experience with production AI/ML systems
• Expert proficiency in Rust for high-performance backend services
• Frontend development skills with modern JavaScript frameworks (React)
• Understanding of AI/ML model integration and tool calling architectures
• Experience with end-to-end encryption implementation and cryptographic protocols
• Knowledge of infrastructure automation and site reliability practices

AI & Privacy Expertise

• Experience with large language models, AI agents, and function calling systems
• Understanding of AI model serving frameworks (e.g. vLLM)
• Knowledge of privacy-preserving technologies and zero-knowledge protocols
• Experience building search systems and information retrieval pipelines
• Familiarity with vector databases and semantic search technologies

Infrastructure & Operations

• Knowledge of monitoring tools (Prometheus, Grafana) and incident response
• Experience with CI/CD pipelines and automated deployment systems

Professional Qualities

• Passion for privacy rights and user-centric AI technology
• Strong problem-solving skills with attention to security and reliability
• Self-motivated with ability to own complex technical challenges end-to-end
• Excellent communication skills for cross-functional collaboration

Preferred Qualifications

• Advanced degree in Computer Science, AI/ML, or related technical field
• Experience with privacy-focused or security-critical applications
• Contributions to open-source AI, privacy, or infrastructure projects

Technical Environment

• Backend: Rust (primary), PHP (integration)
• Frontend: React
• Infrastructure: Ansible, Docker
• Security: Zero-access encryption, PGP/AES protocols
• Monitoring: Prometheus, Grafana, distributed tracing

Why Join Lumo

You'll be joining a mission-driven team at Proton, trusted by over 100 million people worldwide and owned by the nonprofit Proton Foundation. This role offers the opportunity to shape the future of AI by building fullstack infrastructure that proves privacy, performance, and reliability aren't mutually exclusive.

As a Fullstack Applied AI Engineer at Lumo, you'll own the complete technical stack powering privacy-first AI experiences, ensuring millions of users can rely on Lumo for their most sensitive conversations with complete confidence in both AI capabilities and privacy protection.

What We Offer

• Office First: Collaboration is easier and more effective in person, which is why we have offices in Geneva, Zurich, Prague, Barcelona, Paris, London, Vilnius, Skopje, and Taipei. You can also enjoy working from home up to 30% of the time, while enjoying great company during our three core days in the office. 
• Technology: We provide all the devices and software you need to excel in your role, ensuring you have the best tools at your disposal to achieve your goals.
• Food: Lunch and snacks are provided by Proton every day at our offices.
• Transport: We will always support our employees with transport costs through subsidizing public transport, bike allowances, or parking spaces based on your office location.
• Stock Options: At Proton, we are all owners of the company and you get stock options when you join us.
• Flexible Working: You can define your own working hours as long as it works with team meetings.
• Learning and Development: We are committed to your professional growth. Proton offers various learning opportunities, including training programs, conferences and events, and continual learning.
• Employee Benefits: Comprehensive health insurance plans, competitive retirement savings options, generous vacation and leave policies, and wellness programs.
• Work that Matters: Proton is a community-first organization, started with the support of a crowdfunding campaign and built with community input. To this day, Proton’s only source of revenue is user subscriptions. Over 100 million people trust and support Proton, and we put our users and community first in everything we do. Read more about our impact here.

Our Commitment to Diversity and Inclusion

At Proton, we believe diversity drives innovation and strengthens our mission to provide privacy as a default for all. We are committed to fostering an inclusive environment where all individuals, regardless of race, ethnicity, gender, age, sexual orientation, physical ability, or socio-economic background, feel valued and empowered. We strive to create equal opportunities, promote open dialogue, and support continuous learning to ensure every voice is heard and respected.

If you need any extra support or reasonable adjustments during the hiring process, please let your talent partner know.

Candidate Privacy Notice

When you apply for a position, refer a candidate, or are considered for a role at Proton Technologies AG (Proton, we, us, or our), your information is stored in Greenhouse, in accordance with their Service Privacy Policy. This information is used to evaluate your suitability for the posted position. We also retain this information for consideration for future roles that you may apply for or that we believe may align with your background and skills.

If we no longer have a legitimate business need to process your information, we will either delete or anonymize it. Should you have any inquiries about how we use or manage your information, or if you wish to access, correct, or delete your data, please contact our privacy team at careers@proton.ch.

Proton does not accept unsolicited resumes from any sources other than directly from candidates. We will not pay a fee for any placement resulting from an unsolicited offer, even if the candidate is subsequently hired by Proton.

To learn more about our privacy policy, please visit our privacy policy page.

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