Senior Full-Stack Engineer - Stealth Company - Founding Engineer - Vertical AI

Antai Ventures is a Barcelona-based venture studio with presence across Southern Europe and Latam. Since 2012 we have co-founded 35+ companies including Glovo, Wallapop, Piper, PlatanoMelon, and Vitaance. Our ventures have raised more than $1.5B in funding, have generated more than $3B in shareholder value, and currently employ more than 3,000 people. At Antai, we partner up and invest in the best co-founders to build global companies willing to disrupt multi-billion dollar industries. In the last 12 years, we have gained experience in a variety of business models (E-Commerces/DNVBs, B2B SaaS, Marketplaces) operating in a wide range of industries including Edutech, Grocery, Healthtech, Fintech, Insurtech, Proptech, Autotech, among others. We are looking for a Senior Full-Stack Engineer to join the founding team of one of our portfolio companies — a B2B SaaS platform that helps service companies manage the complex, day-to-day operations of their distributed frontline workforce. Think scheduling, real-time coordination, coverage resolution, time tracking, and client communication — all powered by an AI agent that can make phone calls, contact workers, and take autonomous action to keep operations running smoothly. The vision is ambitious: build the operating system for an entire industry — starting with day-to-day operations, then expanding into deeper integrations across finance, HR, and everything else these companies need to run their business. AI isn't a feature we're bolting on — it's embedded from day one as a core capability that fundamentally changes how these companies operate. THE ROLE You’ll be one of the first engineers on a small, high-ownership team building a product from the ground up. This isn’t a role where you’ll be handed tickets — you’ll be researching customer problems, crafting detailed specs, designing solutions, writing code, and shipping features end-to-end. You’ll work directly with the founders and be expected to bring strong judgment about what to build, how to build it, and when to keep things simple. We need someone who is genuinely full-stack: comfortable across backend, database, frontend, mobile (web-based via Capacitor), and cloud infrastructure. You don’t need to be an expert in every layer, but you need the confidence and curiosity to work through problems across the entire stack, learn what’s needed, and find the right solution for the context. 📍 Location: Barcelona, hybrid (some office days) 📝 Employment: Full-time 🎤 Languages: Proficient English required. Spanish not required, but a basic level is a plus. 💰 Compensation: €50–70K + equity WHAT YOU’LL WORK ON - Study customer problems deeply and translate insights into detailed functional and technical specs — then turn those specs into working software. - Design and build core backend systems powering workforce scheduling, real-time coordination, and operational workflows. - Build clean, well-structured APIs and data models that support web, mobile, and internal tools. - Develop the worker-facing mobile experience (web-based, via Capacitor) with a focus on simplicity for low-tech-savviness users. - Contribute to the AI agent’s backend — the infrastructure that lets it resolve coverage incidents, contact workers, and take autonomous actions. - Manage and evolve cloud infrastructure, CI/CD pipelines, and developer tooling. - Improve reliability, observability, and performance across the system. - Build integrations with other business software the industry already uses — accounting, payroll, and other operational tools. - Participate in design reviews and product decisions, bringing engineering perspective to what gets built and how. YOUR FIRST 3–6 MONTHS You’ll ramp up fast. Here’s what that might look like: - Immerse yourself in the domain — studying how service companies actually run their operations day-to-day, reviewing processed customer insights, and building a mental model of the problems we’re solving. - Pick up existing specs,…