Lead Agent Engineer (Langchain) in London

At Focused, we move quickly to deliver quality software that achieves client outcomes and meets their customer’s needs. We strategically partner with our clients to leverage our expertise in design and software, while our clients bring their own domain expertise. We work with a variety of clients from different industries, collaborating as we get new products to market, modernising legacy systems, or helping teams learn the skills they need to be successful.

Our values:

• Listen first: We are experts in product practices but lifelong learners in the domain of our customers. We research, collaborate, and understand.
• Learn why: We ask questions and talk to users to understand problem spaces, objectives, and goals, which allows us to deeply invest and drive towards the outcomes of our clients.
• Love your craft: We love diving into a variety of domains and solving problems. We take pride in delivering value, in communicating progress, and guiding our clients to success.

At Focused, our Engineers are both practitioners and experts in their craft. This role would play a crucial role in shaping and implementing engineering best practices and ensuring the successful delivery of complex software projects. With clients, we develop trust and influence - we are unintimidated and unintimidating. With colleagues, we set the standard for how we deliver success for clients.

What would you be doing?

• Build AI-enabled applications leveraging LangChain and LLMs to deliver meaningful, production-ready outcomes for clients.
• Deep expertise in LangChain, LangGraph and LangSmith.
• Lead teams through end-to-end delivery across the stack, from backend services to modern web UIs.
• Pair program daily with teammates and clients to share knowledge, improve code quality, and grow together.
• Practice TDD and continuous refactoring to ensure code is reliable, maintainable, and understandable.
• Guide architecture decisions to support scalability, observability, and performance.
• Collaborate closely with designers, product managers, and stakeholders to continuously deliver valuable software.
• Coach developers on the team through pairing, mentoring, and modelling healthy engineering culture.
• Influence technical direction beyond the team, working across client orgs and Focused’s internal practices to share lessons, shape approaches, and raise the collective bar.
• Stay curious through experimenting with new patterns in the GenAI space, share what works (and what doesn’t), and help evolve how we build AI-powered software.

We are excited about you, because you:

• You’re a hands‑on, full stack engineer with a strong track record of delivering software in collaborative, agile environments.
• You’ve worked with LangChain (or similar agentic frameworks), and understand how to architect AI-native systems responsibly and effectively.
• You have experience leading engineering teams and feel confident mentoring and supporting other developers.
• You believe that code quality matters, and that TDD and pairing help build better systems and stronger teams.
• You’ve worked across multiple languages or frameworks (e.g., Python, Node, Java, React, Next.js) and are pragmatic about tool selection.
• You’re excited about what’s happening in the AI space but stay focused on delivering value.
• You have experience navigating complex organisations, building bridges across functions, and helping teams adopt modern development practices.
• You’re as comfortable in the code as you are in a client meeting and can translate technical risks and wins into language anyone can understand.
• You love to share what you’re learning and make the team around you better.

If you had worked at Focused over the last 3 months you may have:

• Paired with a teammate to build a document Q&A system using LangChain and OpenAI APIs.
• Helped design an architecture that integrates LLM agents into a legacy enterprise workflow.
• Refactored a flaky test suite to support continuous delivery with confidence.
• Mentored a junior dev through their first pairing and TDD session.
• Built and deployed a full stack GenAI MVP with a React frontend and FastAPI backend.
• Facilitated an architecture spike to evaluate vector database options for semantic search.
• Contributed a new section to our internal AI playbook.
• Helped write this job req.

What to know before you apply:

• This role will require working in person for up to four days per week.
• The London base salary range for this role is £90,000-£125,000.