AI Engineer

Barcelona - Onsite

Pillar was founded in 2025. Today, we are 90+ people, serve 1000+ customers, raised €15.2M (pre-seed and seed round) and are expanding internationally.

We are building the financial operating system for construction: bringing AI, automation and modern software to an enormous industry still full of slow, fragmented processes.

We are looking for an AI Engineer who has already put AI in production in a startup or scaleup, knows what breaks when agents meet real customers and wants to build the AI core of Pillar.

The mission

Build production-grade AI systems that solve real customer problems: reliable, measurable and deeply integrated into Pillar.

What you will do

• Own AI features end to end, from the customer problem to production.

• Build agentic workflows with tool use, structured outputs and multi-step reasoning.

• Turn invoices, reports and forms into structured data our customers can trust.

• Build RAG and semantic search with embeddings, hybrid search and re-ranking.

• Set up evals, tracing and quality checks, so we know when AI gets better or worse.

• Work across our TypeScript stack (Next.js, Supabase, Postgres, Mastra) when a feature needs it.

Who we are looking for

• You have worked in a startup or scaleup, as part of a real team of engineers, product and design.

• You have shipped at least one LLM or agent system to production and kept it running: hallucinations, latency and missing context are problems you have already solved.

• You start from the problem: what success looks like, how much error is acceptable, what it is worth for the customer.

• You know when not to use an LLM: deterministic logic first, models where they add real value.

• You think about cost, latency and an MVP before a v2.

• You build evals early and design systems that improve over time.

• You are strong with SQL and data models (Postgres, pgvector) and productive in TypeScript, or quick to get there.

• You have worked with frameworks like Mastra, LangChain or CrewAI.

• You challenge ideas, accept trade-offs and make the people around you better

• Professional English. Based in Barcelona or willing to relocate

How we work

• Small squads, high autonomy, no unnecessary layers.

• AI-first, in the product and in the way we build.

• Bottom-up: initiative is expected, not delegated.

• Pillar is not for you if your AI work has mostly stayed at POC or pre-sales stage, or if you prefer to work alone.

Hiring process

01 CV screening

02 30-min People call with Marta

03 1-hour conversation with our AI engineers

04 1.5 to 2-hour working session in person on a real Pillar problem (no coding test)

05 Final conversation with our CTO

What we offer

• Gross salary 65.000-80.000 €, based on experience

• Real ownership: you will build core parts of Pillar's AI, from architecture to features customers use every day

• A company that moves fast: 90+ people and 1000+ customers in under two years

• An AI-native team: AI is part of the product and of how we build it

• Close to customers: direct exposure to the problems we solve, with Product, AI and Engineering

• People who care: a team that celebrates wins together, gives honest feedback and has fun along the way.