Software Engineer, Agents

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. Government — 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 visual flows into reliable, observable agent executions
• Set technical standards for the codebase — reliability, testing, code quality, and architecture patterns
• Work across the stack in our Next.js monorepo, shipping to production daily
• Debug hard problems at the intersection of LLMs, distributed systems, and developer tooling

What We're Looking For

• Strong generalist engineer who has shipped complex distributed systems or developer tools to production
• Deep experience with TypeScript/JavaScript and Bun; comfort working in a Next.js monorepo
• Track record of owning and operating production systems — you've been paged, you've debugged the weird ones, you've made things reliable
• Experience integrating with LLMs or building on top of foundation model APIs
• High agency and ownership — on a team this small, you define the roadmap as much as you execute it
• Strong opinions on architecture, loosely held — you care about building things right but move fast
• Experience with AWS infrastructure is a plus
• Contributions to open-source projects are a plus

Why Sim

• Foundational impact. You're not joining a team — you're building one. Every decision you make shapes the product and the company.
• Real users, real scale. 70,000+ developers use Sim today. Your work ships fast and matters immediately.
• World-class backers. Series A - Standard Capital, Paul Graham, Perplexity, SV Angel, and Y Combinator believe in what we're building.
• Open source at the core. We've been open source from day one and we're proud of it. 26,000+ GitHub stars and growing.
• Competitive salary + meaningful equity. Early team, significant ownership.
• Full benefits. Comprehensive health insurance, relocation.
• Visa sponsorship available.