Senior Full-Stack Developer - Freelance (Vitoria-Gasteiz)

About the Opportunity

We're partnering with a stealth AI company building infrastructure that powers reinforcement learning (RL) environments for some of the world's leading AI labs. Their systems operate directly within the AI training loop, helping evaluate, improve, and deploy next-generation AI models. This is highly applied, production-focused engineering work with real-world impact. We're looking for exceptional Full-Stack Software Engineers who thrive in fast-paced environments, take ownership, and can independently ship complete applications from idea to deployment.

Responsibilities

• Build full-stack applications end-to-end (frontend, backend, and infrastructure)
• Deliver high-quality software rapidly without sacrificing maintainability
• Own projects from specification to deployment with minimal oversight
• Use modern AI coding tools (Cursor, Claude Code, Codex, etc.)
• Work primarily through asynchronous communic...