Senior Full Stack Engineer (Back-End)

About the role

⚠️ PLEASE READ FIRST

- This is a full-time, in-person role based in San Francisco (Presidio) - we work from the office 5 days a week.

- You must be based in the Bay Area or willing to relocate before starting.

- We require US work authorisation, but are open to O-1 or J-1 visa sponsorship for exceptional candidates.

ABOUT SAUNA BY WORDWARE

Every tool you use was built as an island, so you became the glue between them: a name from Gmail into the CRM, a time from the CRM into Calendly, a note from Calendly into a doc. AI showed up and mostly became an eleventh window to paste into.

Sauna is a hybrid of AI and software standing on one shared brain. It holds your context and hands you real software built on top of it, so an ordinary Calendly becomes one that writes the invite itself and knows which of your busy hours bend, and for whom. Software for the path you repeat, AI for the edge that never repeats.

Wordware is the team behind it, 15 people backed by Spark Capital, Felicis, and Y Combinator with a $30M seed, the largest in YC's history. We build from an office in the Presidio, fifty metres from Crissy Field beach, and we work absurdly hard because we can see and feel the outcome every day.

ABOUT THE ROLE:

You'll write and ship full-stack features end to end, from the agent runtime and backend APIs, to the web and desktop UI that users interact with every day.

We're still ~20 people and shipping to our first paying users. You won't just be building features, you'll be making the decisions that determine whether this system holds at 1000x the current load.

What You'll Do:

You'll work directly with our CTO. Here are a few examples of the kinds of things you might work on:

- Build and operate the sandbox infrastructure where agents execute code, process isolation, resource limits, secure credential handling across thousands of concurrent sessions.

- Design the deployment and migration pipeline for a Cloudflare Workers + Fly.io http://Fly.io http://Fly.io architecture, including blue-green rollouts and canary patterns.

- Instrument real-time workloads end to end: SSE streaming, task queues, and multi-model LLM provider routing.

- Ship new backend capabilities, tool integrations, scheduled task execution, memory indexing, and see them used by real people the same week.

- Reduce operational toil for a small team: structured logging, tracing, monitoring, and incident response tooling that actually works at our scale.

- Plus whatever you see that needs building.

Stack:

TypeScript, Cloudflare Workers, Durable Objects, Hono, Drizzle ORM, Postgres, Zod, Vercel AI SDK, Docker, React, Vite

Who You Are:

Minimum:

- You have 5+ years of engineering experience building and operating backend systems in production. You've been on-call.