# Senior Full-Stack Software Engineer, AI Core

**Company:** [Circle](https://hotfix.jobs/companies/circle)
**Location:** Remote
**Role:** Fullstack Engineering
**Salary:** $130k – $140k/yr
**Experience:** 6+ years
**Skills:** Ruby on Rails, React, MySQL, Postgres, artificial intelligence, RAG, AI Agents, LLMs, A/B Testing, ai evaluations, query optimization, database migrations, Performance Optimization, AI Infrastructure, production inferencing
**Posted:** 2026-08-12

> Build and scale full-stack AI features across Ruby on Rails and React, from experimentation through reliable production deployment. The role requires 6+ years of experience with high-traffic applications, production AI use cases, and strong experimentation and performance optimization skills.

## Job Description

## Responsibilities
- 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 and AI evaluations, to validate AI features, measure impact, and guide iteration.
- Build and integrate AI infrastructure components 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.
- Stay current with AI research, techniques, and tools.
- Collaborate with leaders and designers throughout the feature design process.
- Prioritize speed of iteration, experimentation, and learning while maintaining high standards of code quality and user experience.

## Requirements
- 6+ years of experience as a full-stack engineer working on high-traffic production applications.
- Experience with query optimization, careful migrations, and performance bottlenecks at scale.
- Strong proficiency in Ruby on Rails, MySQL or PostgreSQL, and React.
- Hands-on experience building AI features in production, such as RAG systems, AI agents, or LLM-powered tools.
- At least one shipped production AI use case, beyond prototypes.
- Experience designing and running A/B tests, measuring results, and iterating based on findings.
- Ability to work autonomously and collaboratively in a fast-paced, ambiguous environment.
- English proficiency at CEFR Level C2 / ILR Level 5.

## Compensation and Benefits
- $130,000–$140,000 USD per year.
- Equity with ongoing refresh grants.
- 35 days of paid time off annually.
- Remote-only work arrangement.
- Twice-yearly company retreats.
- Benefits supporting health, wellbeing, and professional growth.

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