Senior Full Stack Engineer

Urgent hire. Backend-leaning full-stack engineer working directly with the CTO to build and scale core infrastructure for a $30M seed-stage AI platform. 5 days a week on-site at the Presidio, San Francisco. Full-time. What You'll Build Core backend infrastructure: agent runtimes, SSE streaming pipelines, task queues, and multi-model LLM provider routing, shipped to real external users. Edge compute layer using Cloudflare Workers and Durable Objects with Fly.io blue-green and canary deployments. Real-time systems at scale: WebSockets, SSE, event streaming, and message queues under production load. Distributed system architecture: consistency tradeoffs, failure modes, and operational runbooks for a 15-person team moving fast. On-call rotation: you carry a pager, respond to incidents, and own resolution end to end. Required 5+ years of production backend engineering, including on-call. Can name a specific incident, what broke, and how it was resolved. TypeScript fluent, backend-primary. Full stack across the production stack: TypeScript, Cloudflare Workers, Durable Objects, Hono, Drizzle ORM, Postgres, Zod, SST, Vercel AI SDK, Docker, React, Vite. Has shipped real-time systems to external users in production: WebSockets, SSE, event streaming, or message queues, with specific scaling bottlenecks they can describe. Has designed distributed systems and made concrete consistency tradeoffs. Can explain what they chose, what they gave up, and why. Has shipped infrastructure that real external users depended on, not internal tooling. Can name the system, the user load, and the operational responsibility they held. Has worked with LLM agent loops, model routing layers, or tool-use architectures. Does not need ML depth, but must not be starting from zero on agent interaction patterns. Based in San Francisco Bay Area or willing to relocate before the start date for 5-days-a-week on-site work at the Presidio. Visa and relocation: US work authorization required. O-1 or J-1 sponsorship considered for exceptional candidates only. H-1B is not on the table. Europeans eligible for O-1 are considered. US-based candidates are prioritized. Disqualifiers No US work authorization and not O-1 or J-1 eligible. Unwilling to work on-site 5 days a week in San Francisco. Not negotiable. Pure frontend background with no substantial production backend or distributed systems experience. No exposure to agent loops or model interaction patterns. The ramp from zero is too large for this hire. Built only internal tooling, never shipped infrastructure to external users. Needs written specs and fully async communication to function. The office is small, open, and high-energy. Information flows through direct, impromptu conversation. Strong plus Production experience with Cloudflare Workers, Durable Objects, or serverless edge compute. Has built agent runtimes, model routing layers, or tool-use architectures with LLMs in production. Ex-founder or ex-CTO. Most of the current team are former founders or CTOs. Signals high agency and comfort with ambiguity. Early engineer at an AI-native startup. The existing team came almost entirely from small AI-native companies. Actively building or experimenting with AI outside of work, not just following the space. Has tried the product before interviewing. Open to a paid in-person work trial of a few days up to two weeks. Roughly 70% of trial candidates convert to full-time. Accommodation and flights covered for relocating candidates.