Staff Software Engineer, Gustie Assist

Gusto's mission is to grow the small business economy by handling payroll, health insurance, 401(k)s, and HR for small businesses. They support more than 500,000 small businesses nationwide with teams in Denver, San Francisco, and New York.

Gustie Assist builds Otto, the AI agent that Gusto's support advocates rely on to solve customers' hardest payroll, benefits, and compliance problems. As a Staff Software Engineer, you'll own an LLM agent runtime and the full stack around it, including the tool layer, Rails/GraphQL backend, advocate-facing frontend, and eval system.

• Design and build across the Otto platform, including the runtime and agent graph, tool/action layer, Rails/GraphQL backend, and advocate-facing experience, owning a meaningful slice end-to-end.
• Expand what the agent can safely do: autonomous, tool-using actions with human-in-the-loop approval, built on a secure, auditable identity and permissions model.
• Build the eval and observability systems (LLM-as-judge + deterministic scorers, offline gates and online production monitoring) to enable weekly production changes without regressing correctness.
• Work directly with LLMs, including prompting, tool/function design, retrieval, and feedback loops.
• Partner with Product, Data, Design, and CX teams to turn advocate and customer pain into shipped capabilities.
• Mentor engineers and set the bar for building agentic systems responsibly and at scale.

• Typically 8+ years of software engineering experience, owning systems end-to-end.
• Experience building and shipping LLM-powered or agentic systems in production, including tool-calling/agents, retrieval, or evals.
• Strong full-stack range, comfortable moving between backend services, LLM runtime, and customer-facing product.
• Experience owning multi-quarter projects that make measurable user impact at scale.
• Sound judgment about safety and blast radius when software takes real actions on real accounts.
• Ability to mentor engineers and raise the bar around you.

• Experience with agent frameworks, evals/LLM-as-judge, retrieval, or MCP-style tool architectures.
• Experience with Ruby on Rails and/or JavaScript/React, or the ability to ramp quickly.
• Familiarity with GraphQL and federated backends.

All full-time employees receive competitive base pay, benefits, and equity (RSUs). Offer amounts are determined by role, level, and location.

This role is hybrid in Denver, CO; New York, NY; or San Francisco, CA. Employees based in those locations are expected to work from the office on designated days approximately 2-3 days per week.

Apply through the provided Greenhouse link.