Founding Software Engineer - YC Backed AI Startup

Day One Partners is working with a Y-Combinator backed AI startup that’s building a platform for product and engineering teams to integrate Large Language Models (LLMs) into their software. They are growing fast and looking for a Founding Full Stack AI Software Engineer to join their core team.

This role is fully in-person, working side-by-side with the CEO, CTO, and engineers at their Woodland Hills, Los Angeles office. It’s a hands-on, high-impact opportunity to help shape both the product and the company at an early stage.

About the Role

As a Founding Engineer, you’ll play a critical role in designing and building AI-powered tools for software teams. You’ll work across the stack, collaborating directly with leadership to deliver features that solve customer problems. This isn’t a role for someone who just takes tickets—this is for someone who cares about the user experience, wants to know how their code impacts customers, and is excited to build from scratch.

What You’ll Do
• Work closely with the CTO and founding team to design and develop core product features
• Build end-to-end systems across the stack (frontend, backend, and AI components)
• Develop AI-powered features using LLMs and frameworks like LangChain, Llama Index, and OpenAI
• Implement scalable architectures with a focus on reliability and performance
• Ship production-ready code with proper testing and documentation
• Directly impact product decisions and strategy based on customer feedback

What We’re Looking For
• Currently located in Los Angeles (required)
• 4+ years of software engineering experience, including at least 1 year at a senior level
• 2+ years of hands-on experience developing AI applications with LLMs, including retrieval-based methods, fine-tuning, or agent-based architectures
• Experience with AI frameworks such as LangChain, Llama Index, OpenAI, or similar
• Strong skills in Svelte, Python, TypeScript, and Postgres
• Excited to work in-office, Monday through Saturday, with a small, tight-knit team
• Comfortable in an early-stage startup environment where speed, ownership, and learning are core to success

Nice to Have
• Experience deploying, monitoring, and maintaining LLMs in production
• Previous startup experience, especially in fast-growth environments

Why Join
• Get in at the ground level of a Y-Combinator backed AI startup with a proven leadership team
• Work alongside highly experienced founders with track records scaling companies to $100M+ in revenue
• Build products that help teams bring AI-powered features to their users without the need for in-house AI expertise
• Have a major impact on the company’s success and growth
• Competitive salary and meaningful equity
• Be part of a fast-moving team that values hard work, customer focus, and continuous learning

If you’re an engineer passionate about AI and excited to help build a foundational platform, reach out to Day One Partners to learn more. For immediate consideration, email your resume to [email protected] with the subject Day One <> YC SWE

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