Senior Full Stack Engineer (Back-End)

Sauna by Wordware; San Francisco (CA); On-site; USD 180,000 - 240,000; Full time

Benefits offered by this job

Health

Dental

401(k)

PTO

Gym budget

Lunch

Job summary

Sauna by Wordware, based in San Francisco, is hiring for a full-time, in-person backend/Full-Stack role. You will build end-to-end features across agent runtime, backend APIs, and web/desktop UI, operating a sandboxed environment and handling thousands of concurrent sessions.

You will join a small team near the Presidio, with strong emphasis on reliability and scale. You will work directly with the CTO, shipping new backend capabilities, tool integrations, and real-time workloads while shaping

Qualifications

• 5+ years of engineering experience building and operating backend systems in production.
• Fluency in TypeScript and comfort across the stack, with backend focus.
• Experience with real-time systems (WebSockets/SSE) in production.
• Distributed systems intuition and opinions on consistency tradeoffs.
• Shipped infrastructure used by real users, not just internal tooling.

Responsibilities

• Write and ship full-stack features end to end, from the agent runtime and backend APIs to the web/UI users interact with daily.
• Build and operate sandbox infrastructure for agents, with secure credential handling and scaling.
• Design deployment pipelines and migrations (Cloudflare Workers + Fly.io) with blue-green rollouts and canaries.
• Instrument real-time workloads end to end: streaming, queues, and model routing.
• Reduce operational toil with structured logging, tracing, monitoring, and incident response tooling.

Skills

Backend experience

TypeScript

Real-time systems

Distributed systems

Production infrastructure

On-call experience

Tools

Cloudflare Workers

Durable Objects

Postgres

Docker

Vercel

Job description

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

Minimum

Who You Are:

• 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