Principal Software Engineer React + Node Remote EU or USA

pubGENIUS is a React.js and Next.js development agency and ad-tech startup. We build websites and apps for clients across the US and Europe, specializing in decentralized finance (DeFi, crypto, NFT, blockchain), fintech, and healthcare, with occasional work in e-commerce and other verticals.Beyond client work, we operate our own high-revenue web product with a website, mobile app, and machine learning systems powering our ad-tech optimization engine. Performance is not a preference here, it is a core requirement.We are looking for a Principal Software Engineer, who will be the technical authority, responsible for all development, architecture decisions, and long-term technical strategy across a website, mobile app, and ML-powered ad-tech optimization systems.This is a full-time independent contractor engagement. You will work hands-on at a senior level where site speed and server performance are core success metrics. You will work directly with stakeholders to set technical direction, remove bottlenecks, and ship production-grade code.Engagement Details: Type: Full-time independent contractor or EOR Hours: Full-time commitment expected Location: Remote Clients: US and Europe Rate: Competitive, based on experience What You'll Own End-to-end technical ownership of a high-revenue web platform and mobile app Architecture design and long-term technical strategy Server-side rendering pipeline using Node.js, Fastify 5, and React 19 Data layer across MySQL and BigQuery GCP infrastructure including Cloud Run, Cloud Build, and Global Load Balancer Ad-tech integrations including Google Ad Manager, GTM, GTag, and GPT.js Performance optimization at scale, where every millisecond counts ML pipeline maintenance and optimization for ad-tech performance RequirementsMust-Have QualificationsThese are non-negotiable. Please only apply if you have strong, production-proven experience in all of the following: Node.js with TypeScript in production React in a server-side rendering context MySQL including database design, query optimization, and ORM usage BigQuery for querying and managing large-scale datasets GCP with hands-on experience in Cloud Run, Cloud Build, Cloud SQL, and Load Balancing. GCP certification is a significant bonus Nice-to-Have Experience Ad-tech industry experience including ad serving, yield optimization, and programmatic advertising Affiliate marketing experience, particularly with Anura and Everflow Cloudflare including CDN configuration, caching strategies, and Workers Fastify, especially Fastify 5 patterns Flutter for mobile app contribution Golang or Rust for high-performance service work Machine learning applied to ad-tech optimization (not LLMs or agents) Experience in DeFi, crypto, NFT, blockchain, fintech, or healthcare verticals Benefits Fully remote work Flexible hours Paid vacation and sick days Application Process We do not review applications via LinkedIn DMs or email. Please apply through the application link We do not work with staffing agencies or third-party recruiters. Direct applicants only pubGENIUS is an Equal Opportunity Employer; employment with pubGENIUS is governed on the basis of merit, competence, and qualifications and will not be influenced in any manner by race, age, colour, gender, religion, national origin/ethnicity, veteran status, sexual orientation, marital status, gender identity, mental or physical disability, or any other legally protected status.