Senior Full Stack Engineer (Back-End)

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

Benefits offered by this job

Health insurance

Dental insurance

401(k)

Generous PTO

Gym budget

Lunch

Job summary

Sauna by Wordware in San Francisco (Presidio) is seeking a senior backend engineer to own the sandbox, backend APIs, and web UI accessibly by users. You will help scale and harden the system to handle thousands of concurrent sessions and evolving workloads.

You will design deployment pipelines for Cloudflare Workers and Fly.io, instrument real-time workloads, and ship new backend capabilities while reducing toil for a small, dedicated team.

Qualifications

• 5+ years of engineering experience building and operating backend systems in production.
• Fluent in TypeScript; comfortable across the stack with backend focus.
• Experience with real-time systems (WebSockets, SSE, event streaming, or queues).

Responsibilities

• Build and operate sandbox infrastructure where agents run code with isolation and secure credentials.
• Design deployment/migration pipelines for Cloudflare Workers + Fly.io with blue-green and canary patterns.
• Instrument end-to-end real-time workloads: SSE streaming, queues, model routing.
• Ship backend capabilities, tool integrations, and scheduled tasks used by real users.
• Reduce toil with structured logging, tracing, monitoring, and incident response tooling.

Skills

Backend engineering

TypeScript

On-call experience

Real-time systems

Distributed systems

Tools

Cloudflare Workers

Durable Objects

Postgres

Docker

Vercel

SST

Job description

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. Based in the Bay Area or willing to relocate before starting. US work authorisation required, but 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:

• 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] 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

Visa sponsorship is not available for this role.