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.

Equal Opportunity

Sim is committed to creating an inclusive environment for all employees. We celebrate diversity and are committed to creating an inclusive environment for all team members. We do not discriminate on the basis of race, religion, color, national origin, gender, sexual orientation, age, marital status, veteran status, or disability status.