Senior Full Stack Engineer (Back-End)

This is a role that TechTree is recruiting for on behalf of one of our clients.TechTree is an AI-driven recruitment platform working with high-growth companies.When you apply, our AI Agent matches you not just to this role, but to other relevant opportunities across our network, so one application can unlock multiple roles.Senior Full Stack Engineer (Back-End) — Own the backend of an AI agent runtime. San Francisco, on-site.We're a small, fast-moving team (~20 people) building a hybrid of AI and software standing on one shared brain — real software that acts on your context instead of waiting for you to paste it in. We're backed by top-tier VCs with a $30M seed, and we work from an office in San Francisco's Presidio.You'll write and ship full-stack features end to end — from the agent runtime and backend APIs to the web and desktop UI — while making the calls that decide whether the system holds at 1000x today's load.What You'll Do→ Build and operate the sandbox infrastructure where agents execute code — process isolation, resource limits, secure credential handling at scale→ Design the deployment/migration pipeline for a Cloudflare Workers + Fly.io architecture, including blue-green rollouts→ Instrument real-time workloads: SSE streaming, task queues, multi-model LLM provider routing→ Ship new backend capabilities — tool integrations, scheduled tasks, memory indexing — and see them used within the weekWhat We're Looking For→ 5+ years building and operating backend systems in production; you've been on-call→ Fluent in TypeScript, comfortable across the stack, but your instinct runs backend-deep→ You've built real-time systems (WebSockets, SSE, event streaming, or message queues) in production→ Distributed systems intuition — you have opinions on consistency tradeoffsBase salary $180K–$240K + meaningful early-stage equity, plus health, dental, 401(k), and considerable PTO.What is TechTree?TechTree combines AI agents with a human support team to give candidates a better, more transparent hiring experience.Our AI Agent gets to know your background, experience, and what you're optimising for. It continuously matches you to live roles across our network where there's genuine alignment, not just keyword overlap.Our Human Team is there to support you through the process — answering questions, adding context, and making sure you're never left guessing or ghosted.We only post real jobs. Every role on TechTree is a live, active hire.