Intermediate Backend Engineer (Ruby), AI Engineering, Custom Models

An overview of this role

As an Intermediate Backend Engineer on the Custom Models team, you'll help build and evolve Duo Self-Hosted, a key part of GitLab Duo that lets customers run AI-powered features in fully private environments and connect GitLab to their own AI models. You'll work across a mature codebase using Ruby on Rails, JavaScript, and Python to ship features that give our largest customers control, customization, and reliability as they adopt AI in sensitive and regulated contexts. You'll collaborate asynchronously with backend, frontend, product, and UX teammates across time zones, contributing to everything from new features to production issue resolution. Over your first year, you'll grow into owning projects from proposal through production. As the team returns to evaluating large language models (LLMs) and advancing AI capabilities, you'll also have the chance to deepen your impact at the intersection of AI, DevSecOps, and reliability for customers.

Some examples of our projects:

• Extending Duo Self-Hosted so customers can securely plug in their own LLMs and AI providers
• Improving performance and stability for large enterprise GitLab instances using AI capabilities

What you’ll do

• Contribute to Duo Self-Hosted features using Ruby on Rails, JavaScript, and Python, focusing on secure, reliable integrations between GitLab and customer AI models.
• Collaborate with backend, frontend, product, and UX teammates across time zones to design, scope, and deliver end-to-end solutions in an async-first environment.
• Develop, test, and maintain backend services and APIs (REST and/or GraphQL) with attention to scalability, maintainability, and backward compatibility.
• Write maintainable, well-tested code and participate in code reviews, giving and receiving feedback that improves code quality and team practices.
• Diagnose, troubleshoot, and resolve production issues, contributing to on-call or incident workflows and sharing learnings to prevent recurrence.
• Maintain and improve application quality and stability by addressing bugs, refining tests, and contributing to quality assurance efforts.
• Apply performance-minded thinking to identify and fix bottlenecks in the application and data layer, including SQL queries and background jobs.
• Take ownership of projects from proposal through deployment, iterating based on usage data and feedback from customers and internal stakeholders.

What you’ll bring

• Experience building and maintaining production applications with Ruby on Rails, including work with background jobs, APIs, and data models.
• Comfortable working across the stack in a mature codebase, contributing primarily to backend Ruby while also working with JavaScript and Python where needed.
• Proficiency in designing or extending REST and/or GraphQL APIs with attention to scalability, maintainability, and backward compatibility.
• Hands-on experience integrating large language models (LLMs) into applications, including prompt design and building features powered by generative AI.
• Strong SQL skills and familiarity with relational databases such as PostgreSQL, including writing efficient queries and understanding data modeling.
• Ability to identify and address performance bottlenecks at the application and, where relevant, infrastructure layers.
• Openness to learning, collaborating in an async-first, distributed team, and applying transferable skills from related technologies or domains.

About the team

We’re a distributed Custom Models team with GitLab team members across several European countries, Australia, and Canada. We collaborate closely with the AI Framework, MLOps, and Model Validation teams in an async-first way to deliver end-to-end AI capabilities. Together, we focus on creating a reliable, configurable experience for some of GitLab’s largest customers while exploring new opportunities in large language model evaluation and advancing GitLab’s AI-powered features.