Senior AI Software Engineer

Harnham - Data & Analytics Recruitment; Greater London; Hybrid; GBP 120,000 - 140,000; Full time

Benefits offered by this job

Equity

Hybrid work in London

Job summary

Harnham is seeking a Senior AI Software Engineer in London, a hybrid role offering up to £140,000 base salary with equity. You will join as the first senior engineering hire, shaping both product and engineering culture and driving architecture for production-grade AI systems.

You will own end-to-end features, scale LLM-powered applications and set standards for testing, deployment and code quality while collaborating with leadership on roadmaps.

Qualifications

• Experience building and scaling production LLM-powered applications.
• Strong full-stack engineering background.
• 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.
• Experience within regulated industries or financial services is beneficial but not essential.

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

Full-stack engineering

React

TypeScript

Node.js

AWS

APIs

Education

Tools

PostgreSQL

AWS

REST APIs

Job description

Senior AI Software Engineer

London (Hybrid, 3 days per week)

Up to £140,000 + Equity

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
• Strong full-stack engineering background
• 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
• Hybrid working in Central London
• 25 days holiday plus additional benefit