Senior Full-Stack Engineer — Multi-Tenant AI SaaS (FastAPI + Next.js + Postgres)

We're a productized AI service running an agent runtime — one isolated instance per customer — on a stack of FastAPI, Next.js 14, Postgres, and Docker. We're past MVP and into production hardening: real customers, real revenue, real SLAs. Inherit and improve the existing FastAPI control plane (routes, async SQLAlchemy 2.0 + asyncpg, Pydantic, JWT, Stripe billing, APScheduler) Tighten the Next.js 14 / React 18 / Tailwind / Clerk auth frontend Improve security posture: per-tenant row-level security in Postgres, input validation, rate limiting Performance pass: SSE streaming, DB query optimization, caching layer Work alongside an AI agent engineer and a Twilio specialist (separate hires) Required: 7+ years full-stack production experience Deep FastAPI + async Python (NOT a Flask/Django person retrofitting) Next.js 14 App Router + TypeScript at production scale Postgres at scale — async drivers, RLS, query planning Docker, comfortable with Render or similar managed infra Comfortable inheriting a working codebase — you read before you rewrite Nice to have: Multi-tenant SaaS architecture experience Stripe metered billing Clerk or similar managed auth Sentry, observability Have inherited and improved an AI/LLM-adjacent platform before How we work: This is an ongoing engagement, not a one-off. 20–30 hrs/week. Async-friendly but US time zones strongly preferred for sync calls. We pay $80–150/hr depending on seniority. We are not the lowest bidder's client. Paid 4–8 hour trial task (real codebase work) before any retainer.