Senior Full-stack Engineer, Applied AI

Circle

Location: United States
Job Type: full-time
Salary: $130,000 - $140,000
Posted: July 19, 2025

Job Description

About Us

Circle is building the world’s leading all-in-one platform for online communities. 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 180 (and growing!) team members from 30+ countries around the world. We seek exceptional individuals around the world, set them up to do the best work of their lives, and in turn, create a meaningful impact in their own lives. We don't track hours, but we do manage for high expectations very closely. We collaborate across time zones, are highly async, and like to document a lot.

Twice a year, we bring the whole company together in beautiful places around the world for our company offsites. So far, we’ve hosted offsites in Turkey, Portugal, Mexico, Thailand, Colombia, Italy, Ireland, and more, with still more to come!

About the role

The Applied AI team at Circle is at the forefront of leveraging AI to drive innovation across our company.

We're looking for a Senior Full-stack Engineer, Applied AI, to help drive the development of AI solutions that enhance user experiences across our platform, both internally and externally.

If you're passionate about working on real production use cases of large language models (LLMs) and want to contribute to transformative AI applications, this role is for you.

What you'll be doing

Work autonomously on a product built in Ruby on Rails backend and React front-end.
Ship full-stack AI projects end to end --exciting projects such as AI Agents, Retrieval-Augmented Generation (RAG), Structured Extraction, internal tooling for customer-facing teams, and build infrastructure for LLM inference.
Work closely with Circle's leaders throughout the feature design process.
Work closely with our designers to create a world-class user experience.
Help guide the end-to-end architecture and technical strategy for AI solutions.
Improve processes, tools, and systems to scale AI solutions across Circle.
Optimize AI infrastructure for performance, reliability, and cost-efficiency.
Help us stay up-to-date with the cutting-edge AI research, techniques, and tools.
Foster a bias for action, prioritizing speed of iteration without compromising on the quality of code or user experience.

What you'll need to be successful

6+ years experience working as a full-stack engineer on complex web applications with significant scale (100k+ rpm, 100GB+ databases).
Strong proficiency in at least one programming language commonly used for AI development (Python, JavaScript, TypeScript).
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.
Strong understanding of NLP, ML, and LLM fundamentals - including modern LLM technologies, RAG, and prompt engineering techniques.
Hands-on experience with AI frameworks and tools, such as OpenAI, Anthropic, Hugging Face, LangChain, and vector databases.
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, find our values on our career page if you haven’t read up on them yet.
You are proficient in English (spoken, written, and reading) at a CEFR Level C2 / ILR Level 5.

Bonus points

You have deployed at least one AI Agent to production, with a deep understanding of the entire development lifecycle --from initial concept to final deployment with customer feedback loops.

$130,000 - $140,000 USD per year

The cash compensation range shown is a starting point. In addition to equity, benefits and perks, your cash compensation is subject to an annual review and increase on a once per year basis.

The fun stuff

Fully remote: work from anywhere in the world!
Autonomy and trust to do your job: we care about outcomes over everything else.
Paid time away: all employees are given 35 days of PTO annually. We also offer a paid sabbatical after 5 years.
Generous U.S. benchmarked compensation and startup equity no matter where you are in the world.*
Awesome medical coverage with 100% coverage for you and your family, or medical reimbursement options where applicable!*
Parental leave for parents expanding their family, or just starting one.
Home office stipend to help you get up and running.
Learning & development stipend to help you level up your professional skills.
Annual bonus potential for roles that don't already receive variable income or commission.
Company retreats: Twice a year, the Circle team gets together for a fully paid company retreat in incredible places around the world! We’ve had past retreats in Colombia, Portugal, and Mexico, with more planned on the horizon.

*Your role, location and unique circumstance may affect this.

Diversity, Equity & Inclusion

As a fully-remote international company, diversity is baked into our DNA. Here’s how our CEO, Sid Yadav, frames our hiring mission: “let’s find talent in underserved and under-represented corners of the world, set them up to do the best work of their lives, and in turn, change their life.” To achieve this hiring mission, we offer competitive U.S. benchmarked compensation no matter where someone’s located in the world, and we proactively seek candidates who expand representation of backgrounds, cultures and lived experiences in our teams.

Equal Employment Opportunity

Circle is an equal opportunity employer and as such, we do not discriminate on the basis of race, color, religion, sex, sexual orientation, gender identity, national origin, age, disability, or any other characteristic protected by applicable laws. If you require any accommodations during the recruitment process, please let us know and we will work with you to meet your needs.

How We Use Candidate Data

At Circle, we are committed to protecting your personal information. As a job applicant, the personal data you provide to us is collected and processed in accordance with the General Data Protection Regulation (GDPR) in the EU and the California Consumer Privacy Act (CCPA). This notice outlines the types of personal information we collect, the purpose for collecting it, and your rights.

Information We Collect: We collect the following categories of personal information from job applicants:

Contact information (such as name, email address, phone number)
Employment history and qualifications
Education history
References and any other information you choose to share with us during the application process

Purpose of Collection: We collect this information for the following purposes:

To assess your qualifications and suitability for the position
To communicate with you during the recruitment process
To comply with legal and regulatory obligations

Your Rights Under GDPR and CCPA: You have the following rights regarding your personal information:

The right to request access to the personal information we hold about you.
The right to request the deletion of your personal information, subject to certain legal exceptions.
The right to opt out of the sale of your personal information (Note: We do not sell personal information).

🎯 Who is this job for?

This role is ideal for a Senior Fullstack Engineer with 6+ years of experience in Ruby on Rails, React, and Postgres/MySQL, along with strong proficiency in AI/ML tools and frameworks like OpenAI, LangChain, and vector databases. Candidates should have a solid understanding of LLM concepts, prompt engineering, and infrastructure optimization for AI-driven applications. It's perfect for engineers excited to own end-to-end AI projects in a fast-paced, highly autonomous, remote-first environment.

💬 Potential Interview Questions

How do you approach building and deploying full-stack AI projects end-to-end?
I focus on designing scalable architecture, implementing backend services (Ruby on Rails), developing responsive frontend interfaces (React), and integrating AI components like LLM inference, followed by continuous iteration based on user feedback.
What experience do you have with Large Language Models (LLMs) and related AI frameworks?
I have hands-on experience with LLM tools such as OpenAI, Anthropic, Hugging Face, and LangChain, including working on Retrieval-Augmented Generation (RAG) and prompt engineering to enhance AI-driven user experiences.
How do you balance rapid iteration with maintaining code quality and user experience?
By prioritizing a bias for action, I emphasize fast prototyping with solid testing, code reviews, and collaboration with designers to ensure high-quality, performant, and user-friendly products.
Describe your proficiency with Ruby on Rails, React, and databases like MySQL/PostgreSQL in large-scale applications.
I have extensive experience building robust backend APIs with Ruby on Rails, creating dynamic React frontends, and optimizing relational databases for performance and scalability handling high throughput and large datasets.
How do you stay current with emerging AI research and incorporate new techniques into production?
I actively follow AI research papers, experiment with new models and tools, and assess their applicability in production systems to continuously improve AI features and infrastructure.
What strategies do you use to optimize AI infrastructure for performance and cost-efficiency?
I employ techniques such as model caching, batching inference requests, using efficient vector databases, and scaling infrastructure dynamically to balance latency, throughput, and cloud costs.
Have you worked autonomously on AI product features? How do you manage communication and collaboration?
Yes, I own end-to-end feature delivery while maintaining close communication with product leaders and designers through asynchronous documentation, regular syncs, and feedback loops to align goals and progress.
Explain your experience with Retrieval-Augmented Generation (RAG) and structured data extraction in AI.
I’ve built systems that combine LLMs with external knowledge bases to retrieve relevant information dynamically, and developed pipelines for extracting structured insights from unstructured data for better decision-making.
What challenges have you faced working with fast-paced, ambiguous AI projects and how did you overcome them?
Ambiguity is tackled by rapid prototyping, incremental delivery, close collaboration with stakeholders for validation, and adapting quickly to feedback and shifting priorities.
What makes you a good fit for a fully remote, highly autonomous engineering team?
I’m self-motivated, highly organized, communicate clearly across time zones, embrace asynchronous workflows, and take ownership of my work while contributing proactively to team success.

📋 Job Summary

Circle is seeking a Senior Full-stack Engineer, Applied AI, to build and scale AI-powered features on their platform supporting creators and communities. You’ll work remotely, shipping full-stack projects with Ruby on Rails backend and React frontend, focusing on cutting-edge AI applications like LLMs, Retrieval-Augmented Generation, and AI Agents. This role requires 6+ years of experience in full-stack development, strong Ruby on Rails, React, and AI/ML knowledge, plus hands-on experience with AI tools like OpenAI, Hugging Face, and LangChain. Circle offers competitive US-based salary (\$130K-\$140K), equity, generous PTO, fully remote work, paid sabbaticals, excellent medical benefits, and biannual global retreats.