Leyton CognitX, the AI & Technology consulting arm of Leyton Group, is expanding its team of 200+ AI & Tech experts into Spain. We are looking for a Senior AI Engineer to take technical ownership of complex LLM systems on high-value missions for major international accounts, within a multidisciplinary team of engineers, data scientists and consultants.

What you will do

- Own complex features and LLM systems end to end: advanced RAG, LangGraph agents, evaluation and running in production
- Set code-review and testing standards
- Mentor AI Engineers
- Scope needs with clients and present technical results clearly
- Work across the full stack: front end (React, Angular, Next.js) and back end (Python, Node.js, Java / Spring)
- Deploy through CI/CD (Git flow, PR reviews) applying SOLID, design patterns, clean code and TDD
- Integrate models (OpenAI, Anthropic, open-source)

What we are looking for

- 4–6 years of experience
- Several AI / LLM projects in production
- Ability to pick the right pattern and architecture, and explain why
- Advanced in software engineering, LLM & GenAI (LLM APIs, prompt engineering, RAG, agents, evaluation) and backend, APIs & data (REST, GraphQL, gRPC, SQL and NoSQL, pipelines, search)
- Proficient in DevOps & cloud (CI/CD, Docker, Kubernetes,



AWS / Azure, monitoring) and in architecture, leadership & client delivery
- Master’s degree or engineering school in Computer Science, Mathematics or Data Science, or equivalent
- Fluent English (client interactions and code reviews)
- Location: Sant Cugat del Vallés

Tech stack

Python, TypeScript / Node.js, Java / Spring, FastAPI, React, Angular, Next.js · LangChain, LangGraph, RAG (chunking, embeddings, vector stores), FAISS, Elasticsearch, PyTorch, TensorFlow, Hugging Face · PostgreSQL, Redis, MongoDB, Django, Kafka / RabbitMQ, GraphQL, gRPC, Docker, Kubernetes, Jenkins, Terraform, Ansible, GitHub Actions, AWS / Azure

What we offer

- Challenging, real-world projects with major international clients, with autonomy and ownership
- A technical reference role: mentor AI Engineers and shape engineering standards
- Collaboration with lead engineers and access to cutting-edge technologies
- A dynamic, collaborative and innovation-driven environment
- Opportunities to take on greater responsibility within an international organization
- A high-performance culture: regular feedback and a strong focus on delivering tangible value

📌 Senior AI Engineer (San Cugat del Vallés)
🏢 Leyton
📍 San Cugat del Vallés