Senior AI Software Engineer

Senior Software Engineer – AI & Tech

About Leyton CognitX

Leyton CognitX is the AI & Tech Advisory of Leyton, bringing together a dynamic team of over 200 tech experts and data scientists. We specialize in delivering innovative AI and technology solutions that transform how organizations operate and compete.

Our approach combines strategic advisory services with custom development, enabling businesses to harness the power of AI and advanced technologies. We work closely with each client to design intelligent, streamlined solutions that address their specific challenges and align with their strategic objectives.

At Leyton CognitX, we believe that technology is more than just tools; it's a catalyst for meaningful organizational and technological transformation. Our mission is to empower companies to leverage AI and cutting-edge tech, turning complex challenges into opportunities for growth, efficiency, and innovation.

Leyton's Tech team builds the software solutions our consultants and clients use every day. These include business platforms, a client-facing portal and a growing set of AI products. The team is young, motivated and moving fast into AI engineering with LangChain, LangGraph, agents and MCP. We're now looking for an experienced engineer to help it reach the next level.

Your role

You'll be the technical reference of the team. You'll design and build software solutions end to end, bring AI into them through agents, RAG and MCP integrations, take the lead when production gets difficult and help junior developers grow. You'll work on open problems where good judgement matters as much as good code.

Responsibilities

• Architecture & development: design and build scalable software solutions end to end, covering APIs, business logic, front end, databases and security.
• AI integration: build and run AI features in production: RAG pipelines, LLM agents, MCP servers and tool integrations, prompt and context engineering, plus evaluation and cost control.
• Cloud & infrastructure: deploy and run solutions on the cloud, including AI services and GPU-backed inference when it makes sense.
• Critical situations: own production incidents. Diagnose fast, coordinate the fix and run blameless postmortems.
• Code quality: set and apply standards (SOLID, Clean Architecture, design patterns) and lead thorough, constructive code reviews.
• Testing & delivery: define the testing strategy (unit, integration, e2e, evals for AI features) and keep CI/CD pipelines reliable.
• Mentoring: coach junior developers and interns through pairing, reviews and regular feedback.
• Tech watch: follow the AI and software engineering ecosystem, test new tools on real use cases and share what works with the team.
• Collaboration: work with product, DevOps, security and business teams, and explain technical choices in plain language.

Required skills

Software engineering

• Full mastery expected
• Back-end: strong experience with Python (FastAPI or Django) and/or PHP (Laravel) and/or TypeScript (NestJS)
• Front-end: a modern framework (React, Vue.js or Nuxt.js)
• OOP & clean code: SOLID, design patterns, dependency injection and refactoring
• APIs & security: REST design, authentication (OAuth 2.0, SSO, JWT), WebSockets and streaming, security best practices (OWASP)
• Databases: PostgreSQL (data modelling, indexing, query optimisation, migrations) and Redis. MongoDB is a plus.
• System design: scalable, resilient architectures and their trade-offs, including caching and message queues (RabbitMQ, Kafka)
• DevOps: Docker, Git, CI/CD (GitHub Actions, GitLab CI or Azure DevOps) and monitoring. Kubernetes and Terraform are a plus.

AI engineering

• LLM integration: OpenAI, Anthropic and open-source model APIs, prompt engineering, structured outputs, streaming, and token and cost management.
• Agents & MCP: LangChain, LangGraph or equivalent, tool calling, building and connecting MCP servers, guardrails and human-in-the-loop.
• RAG: chunking, embeddings, vector stores (pgvector, Qdrant, Pinecone…), hybrid search and re-ranking.
• Quality & safety: evaluation datasets, monitoring (LangSmith, Langfuse…), prompt injection defences and data privacy (GDPR, Law 09-08).

Cloud & GPU

• Cloud: hands-on experience with Azure, AWS or GCP, including their managed AI services (Azure OpenAI, Bedrock, Vertex AI).
• GPU: working knowledge of GPU infrastructure for running open-source models (vLLM, Ollama or similar), including choosing GPU instances and weighing cost, latency and throughput.

Profile

• Engineering degree or Master's in Computer Science or a related field, with 5+ years of software development experience.
• You have built and shipped AI-powered features in production, such as agents, RAG systems or MCP integrations.
• You have already led or mentored developers, and you enjoy making others better.
• You stay calm under pressure. You've handled production incidents and know how to keep people informed while fixing them.
• You're pragmatic: you choose the simplest solution that works and can explain why.
• You communicate clearly in French and English.
• You're curious and keep up with a fast-moving AI ecosystem.

Tech stack

Python · FastAPI · Django · TypeScript · NestJS · React · Vue.js · Nuxt.js · PostgreSQL · Redis · Docker · Git · CI/CD · Azure · AWS · GCP · LangChain · LangGraph · MCP · OpenAI · Anthropic APIs · Vector DBs · vLLM · Ollama

What we offer

• A key role in a team shaping how Leyton uses AI, internally and with clients.
• Real ownership of technical and architecture decisions.
• Products used every day by Leyton's teams, so your work has visible impact.
• An environment where you learn and share, with weekly tech reviews and internal learning paths.
• A competitive package based on your experience.
• A culture built on excellence, continuous improvement and work-life balance.