Senior Fullstack Engineer

MEET SIENA Siena is the Agent of Record for consumer brands. One agent that owns the entire customer journey, running on a shared intelligence layer no point tool can replicate. Consumer brands run ten or more disconnected tools to manage their customers. We collapse that stack into a single agent. It started with support, the hardest surface a brand has, and it expands from there: Shopping Agent, Social Agent, Siena working alongside a brand's own operators. One agent across every surface, with shared memory, shared context, and shared tools. Hundreds of brands already run real customer volume on Siena in production. This is built, working, and growing, and we are racing to build what comes next. THE TEAM We are a small, fully distributed, global team. We have built leverage into how we work, which is what lets a team this size move at the speed we do. We hire athletes. Everyone here owns real outcomes, defaults to writing over meetings, communicates with directness, and acts the moment they see something worth acting on. Low ego, high standards, fast clock. If you want to own real problems rather than close tickets, keep reading. ABOUT THE ROLE As a Senior Full Stack Engineer, you will own meaningful parts of the platform end to end. You will take ambiguous problems, work out the right approach, and ship reliable, high-performance systems that real brands depend on every day. You will work closely with product to shape scope and roadmap, make real architectural decisions within your area, and do your best work without being managed task by task. This role is for engineers who want ownership and can carry it. WHAT YOU'LL DO - Own features and systems across the full stack, frontend, backend, and infrastructure, from problem definition through production. - Partner with product to break down ambiguous scope and ship in iterative, high-impact releases. - Make real architectural and design decisions in your area, and explain the reasoning so the team can build on it. - Take cutting-edge language models into enterprise customer workflows, where reliability and safety actually matter. - Solve hard engineering problems: API performance, microservices, scaling across channels and brands. - Maintain and improve our AWS infrastructure with a DevOps mindset. - Raise the bar around you. Share what you know, review thoughtfully, and help teammates level up. WHO YOU ARE - 5+ years of software engineering, with real ownership of systems you have shipped and run in production. - Strong full-stack engineer in our core stack: Node.js, React, TypeScript, Express. - Solid with AWS (Fargate, Lambda, EC2, SQS) and with PostgreSQL and Redis. - Comfortable with CI/CD pipelines (CodePipeline, GitHub Actions, or similar). - Experienced with microservices and scalable systems. - Product-focused. You think past the code to customer outcomes and business impact. - You have shipped LLM-powered features to production. This is a must, not a bonus. You know what breaks when models meet real users. - High-ownership and direct. You take initiative, fix problems without waiting to be told, and say openly when something is not working. BONUS POINTS - Next.js. - Infrastructure as Code (CDK, Terraform). - Python. - Event-driven architecture. - Background in customer support or CX software. WHY SIENA? - Real ownership. You will own problems, not tasks, with the autonomy to solve them your way and the trust to do it without a manager in your inbox. - Work that ships and matters. What you build reaches real consumer brands fast. - A category we are creating. The Agent of Record is new ground, with unsolved problems and cutting-edge models, not a crowded field to compete in. - A team that respects your judgment. Globally distributed, async-first, low bureaucracy. We hire adults and treat you like one. - Great salary plus equity or stock grants. Own a piece of what you build. - Learning budget. If you are growing, so are we. - AI-fluency by default. Few places will pu