Senior Full-Stack Software Engineer, AI Core - Circle

About Us

Circle is building the world’s leading AI-powered, all-in-one platform for digital businesses. We make it possible for creators, coaches, educators, and businesses to bring together their audience with engaging discussions, live streams, events, chat, courses, and payments — all in one place, all under their own brand.

We’re proud to be a fully remote company of around 270 team members from 30+ countries around the world. We collaborate across time zones, are highly async, and twice a year we bring the whole company together for international offsites.

About the Role

The AI Core team at Circle is at the forefront of leveraging AI to drive innovation for our customers through transformative applications of large language models (LLMs).

We're looking for a strong full-stack engineer proficient in web frameworks, backend development, and infrastructure to spearhead the development of full-stack AI solutions across Circle. You will work on exciting projects such as AI agents, Retrieval-Augmented Generation, AI evaluations and observability, and building infrastructure for LLM inference.

What You'll Be Doing

• Ship full-stack AI projects end-to-end on a product built with a 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 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, dealing with scale challenges like query optimization and performance bottlenecks.
• Strong proficiency in Ruby on Rails, MySQL / PostgreSQL, and ReactJS.
• Hands-on experience building AI features in production — whether RAG systems, AI agents, or LLM-powered tools.
• Strong experimentation mindset with comfort designing and running A/B tests and iterating quickly.
• Desire to work in an environment that values speed of iteration, individual autonomy, and personal accountability.
• Comfort in a fast-paced environment with a certain level of ambiguity.
• Proficiency in English (spoken, written, and reading) at a CEFR Level C2 / ILR Level 5.