Staff Software Engineer, Core AI Platforms

About Gusto

At Gusto, 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 Gusto should share in its success. Offer amounts are determined by role, level, and location. Learn more about ourTotal Rewards philosophy.

AI is a fundamental part of how work gets done at Gusto. 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 Gusto'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 Gusto 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 Gusto 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