Senior Full-Stack Software Engineer, Applied AI

Role Description

The Applied AI 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 who is 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
• Building infrastructure for LLM inference

While deep AI specialization or expertise isn't required, we care about some hands-on experience building AI features. Beyond that, we’re looking for a strong experimentation mindset. If you're excited about rapidly testing ideas, running A/B experiments, and iterating on real production use cases of LLMs, this role is for you.

The Applied AI team is composed of different backgrounds. Some team members joined with deep Rails experience and solid AI fundamentals, while others joined with deep AI experience and ramped up on Rails. Either path works as long as you bring hands-on experience with both Rails and AI and have genuine curiosity to grow.

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.

Qualifications

• 6+ years experience working as a full-stack engineer on high-traffic production applications.
• Strong proficiency in Ruby on Rails, MySQL / Postgresql, ReactJS.
• Hands-on experience building AI features in production — whether RAG systems, AI agents, or LLM-powered tools.
• Strong experimentation mindset — comfortable designing and running A/B tests, measuring results, and iterating quickly.
• A desire to work in an environment which values speed of iteration and individual autonomy.
• Comfortable in a fast-paced environment with a certain level of ambiguity.
• Strong alignment with our values.
• Proficient in English (spoken, written, and reading) at a CEFR Level C2 / ILR Level 5.

Requirements

• Experience dealing with the challenges that come with scale — query optimization, careful migrations, performance bottlenecks.
• You've shipped at least one real AI use case, not just prototypes.

Benefits

• $130,000 - $140,000 USD per year.
• U.S.-benchmarked compensation globally.
• Equity in the company with ongoing refresh grants.
• 35 days of paid time off each year.
• Incredible flexibility and autonomy.
• A benefits package that supports health, wellbeing, and professional growth.