Senior Full-Stack Software Engineer, Applied AI

What you'll be doing

• Ship full-stack AI projects end-to-end on a product built in Ruby on Rails backend and React frontend.
• Design and run experiments (including A/B tests, AI evaluations, or others) to validate AI features, measure impact, and guide iteration.
• Build and integrate components for AI infrastructure and optimize them for performance and reliability to support production-level inferencing.
• Improve processes, tools, and systems to scale AI features into production-ready solutions.
• Help us stay up-to-date with the cutting-edge AI research, techniques, and tools.
• Work closely with Circle's leaders and designers throughout the feature design process.
• Foster a bias for action by prioritizing speed of iteration, experimentation, and learning, while maintaining high standards of code quality and user experience.

What you'll need to be successful

• 6+ years experience working as a full-stack engineer on high-traffic production applications. You've dealt with the challenges that come with scale — query optimization, careful migrations, performance bottlenecks.
• Strong proficiency in Ruby on Rails, MySQL / Postgresql, ReactJS. Familiarity with both frontend and backend is necessary, but a high degree of proficiency in both is not a requirement.
• Hands-on experience building AI features in production — whether RAG systems, AI agents, or LLM-powered tools. You've shipped at least one real AI use case, not just prototypes.
• Strong experimentation mindset — you’re comfortable designing and running A/B tests, measuring results, and iterating quickly to discover what works and what doesn’t.
• A desire to work in an environment which values speed of iteration and individual autonomy, while also embracing personal accountability and the ability to collaborate effectively as part of a dynamic team.
• Comfortable in a fast-paced environment with a certain level of ambiguity, especially when learning and picking up new technologies when projects require it.
• Strong alignment with our values.
• You are proficient in English (spoken, written, and reading) at a CEFR Level C2 / ILR Level 5.

Compensation $130,000 - $140,000 USD per year Circle offers U.S.-benchmarked compensation globally, equity in the company with ongoing refresh grants, and 35 days of paid time off each year.