Staff Software Engineer, Core AI Platforms

About Halcyon Labs At Halcyon Labs, we're on a mission to grow the small business economy. We handle the hard stuff — payroll, health insurance, 401(k)s, and HR — so owners can focus on their craft and their customers. With teams in Denver, San Francisco, and New York, we support more than 500,000 small businesses nationwide and are building a workplace that reflects the people we serve. All full-time employees receive competitive base pay, benefits, and equity (RSUs) — because everyone who helps build Halcyon Labs should share in its success. Offer amounts are determined by role, level, and location. Learn more about our Total Rewards philosophy . AI is a fundamental part of how work gets done at Halcyon Labs. We expect all team members to actively engage with AI tools relevant to their role and grow their fluency as the technology evolves. AI experience requirements vary by role and will be assessed during the interview process. About the Role: We're looking for seasoned full-stack software engineers to join the teams behind Halcyon Labs's AI product platforms — the shared systems that our product teams build upon — to serve small business owners every day. As a Staff Software Engineer, you'll operate across the full lifecycle of foundational systems: deliver production AI agent systems — multi-agent orchestration, tool/workflow registries, agent-to-agent handoffs, human-in-the-loop escalation, and long-running conversation state, shaping architecture early in the design process, building self-service internal features and APIs, and owning their performance long after launch. That means engineering the core business engine, enabling product teams with reliable backend services, and setting the engineering standard for those around you. If you're drawn to work that combines technical craft with real-world impact — helping power the livelihoods of millions using Halcyon Labs products — join us! Here’s what you’ll do day-to-day: Design and maintain evaluation frameworks across offline and online environments — including golden datasets, LLM-as-judge pipelines, and production replay — while establishing regression gates and end-to-end observability and tracing for agent runs Design, build, and test Halcyon Labs core platform services – communications, reporting, dashboards, access, workflows, risk, payments, and compliance capabilities, among others Mentor other engineers to help solve some of the hardest technical problems out there in very complex domains and at a large scale Help scale one of the largest Ruby/Rails and Javascript/React applications in the world Collaborate with our Product Engineering, Product Management, Data, and Design teams to understand customer pain points, come up with solutions, and then prototype, iterate, and launch daily Build platforms that engineering teams rely on, and trust to deliver products that our customers genuinely love Here’s what we're looking for: Successful applicants typically have 8+ years of software development experience Hands-on experience taking AI/LLM capabilities to production — agent orchestration, tool integration, retrieval, and evaluation/feedback loops that keep AI improving safely AI fluency: fluent, daily use of AI coding assistants (e.g., Claude Code, or equivalent AI harness) across the development lifecycle — writing, reviewing, debugging, and documenting code — with strong judgment on when to apply them, how to evaluate output quality, and how to stay current as the tooling evolves Passion for creating scalable, efficient platforms for users Curiosity and experimentation with emerging AI frameworks, applying and sharing best practices to evaluate and scale AI use safely across teams Others: Experience in, or interest working in, Ruby on Rails Appreciation for a collaborative, test-driven environment Ability to build well-structured, maintainable, well-documented code Ability to effectively communicate across engineering teams and with business stakeholders Do you prefer heavy feature development instead? Check out our Staff Software Engineer, Core Products job listing. Please note that a two day travel to a Halcyon Labs office for onboarding is required for this position. If you have any questions regarding this requirement, please share with your recruiter. Our cash compensation amount for this role is targeted at $163,000–$204,000 in Denver & most remote locations, and $197,000–$247,000 for San Francisco & New York. Stock equity is additional. Final offer amounts are determined by multiple factors including candidate experience and expertise and may vary from the amounts listed above. Halcyon Labs has physical office spaces in Denver, San Francisco, and New York City. Employees who are based in those locations will be expected to work from the office on designated days approximately 2-3 days per week (or more depending on role). The same office expectations apply to all Symmetry roles, Halcyon Labs's subsidiary, whose physical office is in Scottsdale. Note: The San Francisco office expectations encompass both the San Francisco and San Jose metro areas. When approved to work from a location other than a Halcyon Labs office, a secure, reliable, and consistent internet connection is required. This includes non-office days for hybrid employees. Our customers come from all walks of life and so do we. We hire great people from a wide variety of backgrounds, not just because it's the right thing to do, but because it makes our company stronger. If you share our values and our enthusiasm for small businesses, you will find a home at Halcyon Labs. Halcyon Labs is proud to be an equal opportunity employer. We do not discriminate in hiring or any employment decision based on race, color, religion, national origin, age, sex (including pregnancy, childbirth, or related medical conditions), marital status, ancestry, physical or mental disability, genetic information, veteran status, gender identity or expression, sexual orientation, or other applicable legally protected characteristic. Halcyon Labs considers qualified applicants with criminal histories, consistent with applicable federal, state and local law. Halcyon Labs is also committed to providing reasonable accommodations for qualified individuals with disabilities and disabled veterans in our job application procedures. We want to see our candidates perform to the best of their ability. If you require a medical or religious accommodation at any time throughout your candidate journey, please fill out this form and a member of our team will get in touch with you. Halcyon Labs takes security and protection of your personal information very seriously. Please review our Fraudulent Activity Disclaimer . Personal information collected and processed as part of your Halcyon Labs application will be subject to Halcyon Labs's Applicant Privacy Notice .