About usWe are a venture-backed startup in stealth, building data infrastructure for the age of AI agents. A small, senior founding team, already working with design partners and early enterprise customers. We value judgment over process and ownership over hand-holding, and we build things that hold up under real load. We will tell you what we are building in conversation, under NDA.The roleYou will own the architecture of the core engine at the heart of our product, hands-on, from the first line of code. This is a principal role that is equal parts research and engineering: many of the hard problems are still open, and your job is to turn them into prototypes, decide with evidence what holds up, and then build production-grade backend systems in Go.We are an AI-first engineering organisation. Engineers orchestrate coding agents for coding, testing, documentation and operations, and stay fully accountable for the result. You will help set the bar for how that works in the most demanding part of our stack.You report to our Head of Engineering and will be one of the first principal engineers on the team .What you bringTen or more years building backend systems, several of them at staff or principal level owning the architecture of a core service.Expert in Go: concurrency, performance profiling, memory behaviour and idiomatic design of large codebases. Strong distributed-systems fundamentals.Hands-on experience building search, query or data-intensive systems at scale, and a deep understanding of how retrieval works for LLM applications.Research ability: you can take an open-ended problem from literature review to working prototype to measured result, and you have a track record of original technical work others built on, whether papers, patents, open source or internal systems.You already orchestrate coding agents as your default way of working, can show concrete examples, and can tell us what you did not trust them with.Systems thinking, high standards, low ego. You disagree hard, then commit fully. Comfort with ambiguity and with the discretion stealth requires.How we work and what we offerWe measure results and ownership, not hours, and we believe in-person time brings out our best work. Hybrid in Madrid, three office days a week together. Agents do the orchestrated work and humans stay accountable. Every iteration puts working software in front of a real user, security is built in, and every non-trivial decision gets an ADR. No assholes, radical transparency on metrics, roadmap and risks, and intensity in seasons rather than permanent burnout.Generous equity: we want early people to share properly in a major success. High-end laptop, private health insurance, 22 working days of holiday. Compensation: a base salary at the top of the Madrid market for principal-level backend engineers, set by how far your experience goes beyond the bar above, plus an early-employee equity grant well above what is usual for the role.How we hireWe hire for the bar, not the gap. An intro conversation, where under NDA we share what we are building. A hands-on session with a real repo and a coding agent. A research deep-dive on a hard problem you took from open question to result. Founder conversations on customers, trade-offs and values, then references.If this role excites you but you don't match every line, apply anyway.

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Principal Engineer. AI-first Engineering