Senior AI Software / Product Engineer

Harnham; Greater London; On-site; GBP 126,000 - 154,000; Full time

Benefits offered by this job

Equity package

First senior engineering hire

Greenfield product ownership

Job summary

Harnham in London is seeking a senior individual contributor to lead the engineering of a greenfield AI platform for financial services. You will own full-stack development, guide architecture, and shape engineering culture from the ground up.

You’ll work across TypeScript, React, Node.js, PostgreSQL and AWS to ship customer-facing features, scale production LLM applications, and define guardrails, deployment, and model routing strategies in a fast-growing environment.

Qualifications

• Experience building and scaling production LLM-powered applications.
• Experience delivering secure, reliable and scalable systems.
• Comfortable working across multiple technologies and learning new stacks quickly.
• Experience with React and modern web applications.
• Product-minded approach with the ability to operate autonomously.
• Passion for building in an early-stage, high-growth environment.

Responsibilities

• Building and shipping customer-facing product features end-to-end.
• Developing and scaling production LLM applications.
• Owning RAG pipelines and AI application architecture.
• Implementing guardrails, evaluations, caching and model routing strategies.
• Working across TypeScript, React, Node.js, PostgreSQL and AWS.
• Building API-first services for enterprise customers.
• Establishing engineering best practices around testing, deployment and code quality.
• Collaborating directly with product and leadership stakeholders to influence roadmap and delivery priorities.

Skills

LLM-powered apps

Security & reliability

Polyglot development

React & web apps

Autonomous/product-minded

Growth-stage experience

Regulated industries helpful

Tools

React

Node.js

PostgreSQL

AWS

Job description

We're partnered with a fast-growing AI start-up building cutting-edge behavioural intelligence technology for the financial services sector. Backed by an exceptional leadership team and industry experts, they're developing a platform that helps organisations better understand client behaviour through advanced AI and large language models.

As their first senior individual contributor engineering hire, you'll play a critical role in shaping both the product and engineering culture from the ground up.

The Opportunity

This is a true 0-to-1 product engineering role. You'll work closely with senior leadership to build and scale a greenfield product, taking ownership across the full stack while driving the architecture and evolution of production-grade AI systems.

You’ll have significant influence over technical direction, engineering standards, product decisions and future hiring as the team grows.

What You’ll Be Doing

• Building and shipping customer-facing product features end-to-end
• Developing and scaling production LLM applications
• Owning RAG pipelines and AI application architecture
• Implementing guardrails, evaluations, caching and model routing strategies
• Working across TypeScript, React, Node.js, PostgreSQL and AWS (Open to different technology backgrounds!)
• Building API-first services for enterprise customers
• Establishing engineering best practices around testing, deployment and code quality
• Collaborating directly with product and leadership stakeholders to influence roadmap and delivery priorities

What We’re Looking For

• Experience building and scaling production LLM-powered applications
• Experience delivering secure, reliable and scalable systems
• Comfortable working across multiple technologies and learning new stacks quickly
• Experience with React and modern web applications
• Product-minded approach with the ability to operate autonomously
• Passion for building in an early-stage, high-growth environment
• Experience within regulated industries or financial services is beneficial but not essential

Why Join?

• Up to £140,000 base salary
• Meaningful equity package
• Opportunity to become the first senior engineering hire
• Direct impact on architecture, product and company direction
• Work alongside talent from leading technology and AI organisations
• Greenfield product with genuine product ownership