Software Engineer, Agents

About this role

About Sim
Sim is the open-source platform to build, deploy, and orchestrate AI agents. Over 70,000 developers — from early-stage startups to the U.S. Department of Defense — use Sim to turn ideas into production-grade agentic workflows on a visual, Figma-like canvas. We connect to 1,000+ apps and LLMs, and our Copilot is the state of the art for building workflows with natural language.


We're a team of 5, YC X25, and backed by a $7M Series A led by Standard Capital with participation from Paul Graham, Perplexity, SV Angel, and Y Combinator. We're based in San Francisco and build in-person every day.


Our mission is simple: agents will run the world, and Sim is the primary means by which that happens.


About The Role
You'll own end-to-end development of our core agentic workflow engine and Copilot — the AI assistant that helps developers build and debug workflows using natural language, turning high-level intent into executable, reliable agents. This spans our backend (Next.js), orchestration layer, and all integrations with LLMs and external APIs.


Copilot is currently the best-in-class tool for building workflows with natural language. Your job is to keep it there and push it further — making it faster, more reliable, and capable of handling increasingly complex agentic architectures.


This is a foundational role. You'll set architecture decisions, reliability standards, and coding patterns that define how the core product works. On a team of 5, your work ships to tens of thousands of developers on fast release cycles.


What You'll Do

• Own the agentic workflow engine: the runtime that executes multi-step, tool-using agent workflows in production
• Build and evolve Copilot — our natural language interface for creating, editing, and debugging workflows
• Design and maintain integrations with LLM providers (OpenAI, Anthropic, Google, local models via Ollama) and external APIs
• Architect the orchestration layer that turns...