Senior Staff API Engineer - Agent & Partner Platform

As a Senior Staff Software Engineer on the Agent & Partner Experiences team, you'll be a key technical leader responsible for influencing the team and broader organization as we build and scale our platform. You'll do this through a combination of hands-on development in our complex Ruby on Rails codebase and guiding others to deliver a high quality platform experience. You’ll sit at the bridge between our API and AI world - turning a payroll platform built for developers into one that agents can reason about and act through.  

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 our Total 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 Team:

Gusto Agent & Partner Experiences is a platform that allows developers to embed payroll directly into their own software using our APIs and allows AI agents to act on payroll on a customer’s behalf. We've taken Gusto’s robust payroll infrastructure and made it available beyond Gusto itself - to third party developers and to the agents acting on their customers’ behalf. Our vision is to enable anyone to build the best payroll product for their end customers - powering payroll for small and medium businesses across a variety of industries, from vertical SaaS to fintech and neobanks to AI-native products.

Learn more about Gusto Agent & Partner Experiences here.

Here’s what you’ll do day-to-day:

• Identify and solve high-impact problems involving technical and organizational complexity that requires understanding and coordination across multiple domains.
• Design the API contracts and agent facing tools our partners and AI agents build on, including what a good interface looks like when the caller is an agent model.
• Engage directly with our developer-customers and internal agent partner to deliver a remarkable payroll product.
• Ship code. Clean, tested, and performant.
• Level up the craft of software engineering across the organization by providing technical guidance and mentoring.
• Inform and maintain best practices for reliability and observability for the team.
• Troubleshoot and resolve production issues.

Here’s what we're looking for:

• Experience: 12+ years of professional software development experience. You have been a technical owner for organization-wide engineering initiatives and have played a role in scaling engineering organizations.
• Technical Expertise: You are a Ruby and Rails expert. You have navigated massive Rails applications, worked with Ruby across multiple codebases, and are comfortable working at multiple layers of abstraction.
• Platform Thinker: You've designed and built platforms and public-facing APIs, and have a strong understanding of how to build for reliability and performance at scale.
• Bar Raiser: You've spent time mentoring and raising the technical bar for the entire organization. Others look to you for guidance on how to tackle ambiguous problems and handle competing priorities.
• Effective Communicator: You think in terms of business priorities and know about how to orient your team around the right technical goals for the business as well as how to convey technical constraints and needs to business leaders.

And a few things that would be bonus - genuinely optional:

• Payroll domain experience: Payroll, tax or fintech experience is a real head start. It’s also learnable, and we’ll teach it.
• Agent facing tooling: Experience designing interfaces consumed by a model - MCP servers, tool and function definitions or an integration path for AI providers. We care how you think about turning an API into a navigable tool surface.
• GraphQL at scale: You’ve been a client of GraphQL - writing efficient queries, building the query construction and data mapping layer around them, and reasoning about performance when you don’t own the resolvers. You have enough schema fluency to influence the design of APIs other teams own.