Senior Full Stack Engineer (Back-End)

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

Most AI products hand you a coworker on day one and hope you trust it. Sauna is the coworker you raise: it starts by learning how you work, earns autonomy task by task, and ends up running hours of work on its own while you keep taste, review, and the final say. Wordware is the ~20-person team behind it, backed by Spark Capital, Felicis, and Y Combinator with a $30M seed, the largest in YC history. We build from a San Francisco office in the shadow of the Golden Gate Bridge, 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 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, SST, 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.

• You're fluent in TypeScript and comfortable working across the stack, but your instinct is to go deeper on the backend.

• You've built real-time systems: WebSockets, SSE, event streaming, or message queues in production.

• You have distributed systems intuition, you understand consistency tradeoffs and have opinions about them.

• You've shipped infrastructure to real users, not just internal tooling.

Bonus (but not required):

• You've worked with Cloudflare Workers, Durable Objects, or serverless compute at the edge.

• You've built agent systems, model routing layers, or tool-use architectures with LLMs.

• You've been a founder or early-stage engineer and care deeply about product.

Compensation & Benefits:

Base salary: $180K-$240K + meaningful early-stage equity + health, dental, 401(k), considerable PTO, gym budget, lunch. x

The Process:

We keep our process simple. Exceptional candidates go from first touch to offer within 2 weeks.

1. Application: Submit your resume and answer a few short questions.

2. 15-minute intro call: Quick check to align on location, motivation, and logistics. If it's a go, we move fast from here.

3. 45-minute technical interview: You'll work through a real backend problem. We're looking for fluency, depth, and how you think about systems.

4. System design interview: A deep dive into how you architect systems. We'll walk through a real Wordware problem together.

5. Final conversation: We answer your questions and scope out the work trial.

6. Work trial: Paid trial to work on a real project in person with us, usually a few days to two weeks (flexible to do what works for you). See how we work and whether this feels like the right fit on both sides.