Senior Software Engineer (AI Agents)

A high-growth startup is building the infrastructure to measure how LLMs actually perceive and process data, giving teams visibility into model behavior that's historically been a black box. They're looking for a Senior Software Engineer to join their founding team. This is a 0→1 opportunity to architect the core product alongside a small, technical founding team. You'll move fluidly between frontend, backend, and applied AI work, including building and orchestrating AI agents end-to-end, with high ownership in a fast-paced, autonomous environment.

This is an onsite role in San Francisco, CA.

What you'll do

• Own full stack architecture decisions from day one, spanning TypeScript/React on the frontend and Python on the backend
• Design and build systems that evaluate and quantify LLM perception of structured and unstructured data
• Build and orchestrate agentic workflows for automated evaluation, data processing, and model behavior analysis
• Work directly with LLMs and model outputs to build novel measurement and evaluation frameworks
• Ship product end to end, from data pipelines to user-facing interfaces
• Set technical standards and engineering culture as one of the first hires

What we're looking for

• Strong full stack experience with TypeScript, React, and Python in production environments
• Hands-on experience building with or around LLMs, whether that's evals, fine-tuning, RAG, or applied AI product work
• Founding engineer, Founder, or very early startup experience, comfortable with ambiguity and fast iteration (must have)
• Bias toward shipping over perfecting, balanced with genuine technical depth
• Excitement about being deeply hands-on at every layer of the stack

Why this role

You'd be one of the first engineering hires at a high growth, well-backed startup tackling a problem that's becoming increasingly critical as LLMs get embedded everywhere. Huge ownership, huge technical surface area, and a seat at the table for foundational product decisions