Backend Engineer

About Cala AI

From the creators of Vilynx - a Barcelona AI startup acquired by Apple - comes Cala AI: a bold new venture redefining how information is verified and represented at massive scale. Based in Barcelona's vibrant tech hub near Passeig de Gràcia, Cala AI is building innovative AI systems focused on trust, accuracy, and impactful technology that challenges industry norms.

Recently, Cala AI was named by Creandum to their #EuroSeed50 list - highlighting the most promising early-stage startups in Europe - an honor that reflects the strong belief in our mission and team. We are a small, ambitious group dedicated to building real solutions with grit, heart, and a culture of authenticity.

We are now growing our engineering team with an experienced Backend Engineer who enjoys working across boundaries - backend, data, infrastructure, and applied AI.

About the role 💡

We're looking for an experienced backend engineer with depth.

You'll come from a Backend Engineering background - Python, APIs, distributed systems - but what matters most is your motivation to build across layers and solve complex problems end-to-end. Backend is your anchor, but this is a high-impact engineering position for someone who enjoys working with multiple parts of the system rather than in a narrow specialization.

You'll work closely with our core team to design, build, and scale the backend systems that power large-scale AI-driven information verification and representation.

What you'll do 🛠️

Design and build backend services using Python (FastAPI)

Architect data storage and retrieval systems using SQL and NoSQL technologies (Postgres, Redis, Cassandra, graph databases)

Develop and maintain scalable pipelines (batch and streaming)

Work with cloud infrastructure on AWS and containerized environments (Kubernetes)

Experiment with emerging AI engineering tooling (coding agents, MCP ecosystems, etc.)

Collaborate on system design and cross-functional architectural decisions

Contribute to a culture of clean, pragmatic, high-quality engineering

Things we value 🔎

Strong background in:

Backend Engineering (Python, APIs, distributed systems)

Technical stack we commonly work with:

Python

FastAPI or similar frameworks

AWS

Kubernetes

SQL and NoSQL databases (Postgres, Redis; Cassandra or graph databases are a plus)

Search systems or information retrieval is a nice to have

DevOps practices

Profile:

4+ years of hands-on backend engineering experience, with real depth - you've gone deep, not wide and shallow

Able to reason about and justify your technical decisions: pros, cons, why A over B

Builders at heart: hackathons, side projects, open-source contributions, active GitHub are all highly appreciated

Curious about how things work end-to-end, including the parts adjacent to your own - infrastructure, data, the systems your code runs on

Curious about the AI ecosystem and modern developer tooling

Comfortable in a fast-moving startup environment

C1+ level in either English or Spanish (fluency in either is acceptable)

Diversity & Inclusion 🌍

We are intentionally building a diverse team. We strongly encourage applications from women, underrepresented groups in tech, and individuals from non-traditional or less represented backgrounds. Diverse perspectives are critical to building responsible AI systems.

If you're excited about the role but don't meet every requirement, we'd still love to hear from you.

Compensation & Work Model 💼

Competitive salary

Stock options

Hybrid model: 3 days per week onsite

New office on Gran Via (Barcelona), with a full dedicated space for Cala AI

Flexible benefits covering transport, meals, and health insurance

Why Cala AI? ✨

Work alongside founders with a proven track record in AI startups

Build foundational AI systems with an "AI for good" focus

High ownership, high autonomy, real technical challenges

Join at an early stage and help shape both technology and culture

A supportive, inclusive, and horizontal team environment

Hiring Process – Conversation-Based (No Coding Tests) 🤝

Initial chat with team member focused on experience and projects

System design interview with CTO (onsite preferred)

Cultural fit conversation with CEO

Offer