Senior Platform Engineer

Location: San Francisco, CA (On-site, 5 days/week)
Employment: Full-time
Seniority: Mid-Senior Level
Salary: $180,000 – $240,000
Visa: US work authorization required. 

About the company
Y Combinator-backed, early-stage AI startup (~15 people) building a hybrid AI and software platform centered on a shared context engine.

The role
You’ll build and own the core execution engine (agent runtime) that manages session state, tool calls, and long-running processes — the backbone that lets AI agents operate reliably over extended sessions.

Core stack: TypeScript, Cloudflare Workers, Durable Objects, Postgres, Docker, Distributed Systems

Required

• Production experience building and operating stateful backend systems — work that outlasts the initial request


• Professional experience writing production backend code in TypeScript


• Based in the San Francisco Bay Area, or willing to relocate

Nice to have

• Experience building an agent runtime or agent harness


• Production experience with Cloudflare Workers, Durable Objects, or other actor-based runtimes


• Experience deploying long-running processes that persist across code releases


• Background at next-gen AI/agentic companies or design-first product orgs

Interview process

• Application review (resume + short questions)


• 15-min intro call


• 45-min technical interview


• System design interview


• Paid work trial (~5 days)

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