Senior Full Stack Engineer (Back-End)

About the role

We are looking for a senior full-stack engineer to design, build and ship end-to-end features for Sauna, an AI-powered coworker platform. You will work closely with the CTO in a fast-moving, 20-person startup, delivering both backend services and user-facing interfaces for our first paying customers.

Key responsibilities

• Design and operate sandbox infrastructure that runs agent code with isolation, resource limits and secure credential handling across thousands of concurrent sessions.
• Build deployment and migration pipelines for a Cloudflare Workers + Fly.io architecture, implementing blue-green rollouts and canary releases.
• Instrument real-time workloads, including SSE streaming, task queues and multi-model LLM routing.
• Develop new backend capabilities such as tool integrations, scheduled tasks, memory indexing and expose them to users within weeks.
• Reduce operational toil by creating structured logging, tracing, monitoring and incident-response tooling that scales.
• Collaborate on UI components using React and Vite, ensuring a seamless experience for desktop and web users.

Required profile

• 5+ years of production engineering experience, including on-call responsibilities.
• Deep expertise in TypeScript and a strong bias toward backend development.
• Proven experience building real-time systems (WebSockets, SSE, event streaming or message queues).
• Solid understanding of distributed systems trade-offs and consistency models.
• Track record of shipping infrastructure that serves external users, not just internal tools.

Required skills

• TypeScript
• Cloudflare Workers
• Durable Objects
• Hono
• Drizzle ORM
• PostgreSQL
• Zod
• SST
• Vercel AI SDK
• Docker
• React
• Vite

What we offer

• Full-time, on-site role in San Francisco with a competitive equity package.
• US work authorization required; O-1 or J-1 visa sponsorship available for exceptional candidates.
• Opportunity to shape core product architecture and impact thousands of users.