Founding Engineer - Backend & AI Systems

Join to apply for the Founding Engineer – Backend & AI Systems role at Relixir (YC X25) Join to apply for the Founding Engineer – Backend & AI Systems role at Relixir (YC X25) Get AI-powered advice on this job and more exclusive features. This range is provided by Relixir (YC X25). Your actual pay will be based on your skills and experience — talk with your recruiter to learn more. Base pay range $150,000.00/yr - $250,000.00/yr Location: In-person, SF Requirement: BS in Computer Science from Top US Unverisity (Stanford, Berkeley, MIT, GeorgiaTech, etc.) Stack: Python, FastAPI, PostgreSQL, AWS (ECS, Fargate), Qdrant, TypeScript Backend Infrastructure What You’ll Work On Building and scaling services in Python (FastAPI) with PostgreSQL as our primary database. Managing AWS infrastructure — primarily ECS/Fargate, Lambda, S3, and related services. Designing APIs for our frontend (TypeScript) and partner integrations. AI/ML Engineering Building agentic workflows and pipelines for large-scale LLM calls (OpenAI, Gemini, Perplexity). Designing and maintaining RAG (Retrieval-Augmented Generation) systems using Qdrant for vector search. Optimizing prompt engineering, retrieval strategies, and evaluation systems. The ROLE You are not just an employee – you are a builder of the company. You’ll be at the core of shaping Relixir’s product, technology, and trajectory – from hands-on backend and AI engineering, to collaborating on the big decisions that define our future. Strategic Impact – Work directly with the founders to influence technical and product direction, deciding how we scale our platform and what bets we make in AI search automation. End-to-End Ownership – Take ideas from rough concept to production-ready systems – APIs, infrastructure, AI agents, and everything in between. You’ll own critical backend modules and ensure they’re fast, reliable, and a joy to use. AI Systems Engineering – Design and deploy large-scale AI workflows – multi-agent pipelines, RAG architectures with Qdrant, and high-volume LLM call orchestration. Customer-Driven Development – Talk to customers, dig into their needs, and turn feedback into technical solutions that directly impact their growth. About You Deeply Curious — You actively seek to understand complex systems, customer problems, and the latest technical possibilities. Curiosity drives your best work. Relentlessly Driven — You thrive in early-stage chaos. You move quickly, test bold ideas, and turn uncertainty into working solutions. True Owner — You don’t just “complete tickets.” You take full responsibility for delivering outcomes — finding a path forward even with incomplete information. Collaborative & Humble — You share ideas openly, listen actively, and care more about the best solution than being right. You’re confident in your skills but always learning. Must-Haves In-person SF High-agency 3 years of experience building backend & AI software for VC-backed startups Strong proficiency in Python and TypeScript Experience with Docker, FastAPI, PostgreSQL, and AWS Built and deployed a complex agentic/LLM-backed (context engineering, RAG with vector db) into production to customers Have completed at least one 0 -> 1 journey of a functional product Nice-to-haves Experience working with any of AWS ECS SQS Fargate, QDrant, LangChain Entrepreneurial Mindset: Ex-founder or future founder Why This Role is Special We're Growing 166% MoM, Onboarding Monster Logos (Rippling, Airwallex, Hackerrank, Etc.), Supporting Global Marketing Teams, And On Our Way To Series A By EOY. This August, I'm Looking For The Most Cracked Top 1% Founding Engineers And Founding Customer Success/ops To Join Our Rocketship Here's My Pitch To You Our product is far ahead of the competition. Companies are switching to us every week because they see the differentiation & immediate value. Revenue pipeline is already at $X,000,000 Customers now see Relixir as the unified solution to automate their entire SEO/GEO Growth Marketing function: a $400B market opportunity. We're backed by Y Combinator and legendary operating investors like z21 Ventures who have built unicorns from scratch. Lastly, our team is a group of nonchalant, hardworking, super chill college dropouts from Berkeley who have scaled and even exited previous companies for 7-figures. Seniority level Seniority levelMid-Senior level Employment type Employment typeFull-time Job function Job functionEngineering and Information Technology IndustriesSoftware Development Referrals increase your chances of interviewing at Relixir (YC X25) by 2x Get notified about new Back End Developer jobs in San Francisco, CA . 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