Senior Product Engineer - 200742

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

Benefits offered by this job

Equity

Hybrid work

London-based role

Ownership of engineering direction

Job summary

Harnham in London is seeking a Product Software Engineer to take ownership of developing and scaling an AI-powered platform in an early-stage startup environment.

You will build LLM-enabled features for enterprise customers, design backend services and APIs, own RAG workflows, monitor quality, and align the roadmap with product leadership and clients.

The role offers meaningful equity, hybrid London work, and the chance to influence engineering culture from day one.

Qualifications

• Strong experience as a Product Software Engineer.
• Proven track record building and shipping an LLM-based product from 0 to 1.
• Experience owning architecture, product decisions, and implementation.
• Strong backend engineering experience with API-first products.
• Hands-on experience with RAG and production AI systems.

Responsibilities

• Building LLM-enabled products and features used by enterprise customers.
• Designing and developing backend services, APIs, and platform capabilities.
• Owning RAG workflows and AI application architecture.
• Managing evaluation frameworks, testing, monitoring, and quality standards.
• Optimising LLM performance, scalability, and cost efficiency.
• Working closely with product leadership and customers to shape the roadmap.
• Establishing engineering best practices across development and deployment.

Skills

Product software engineer

LLM-based product

Backend engineering

API-first

RAG

Cost optimisation

Autonomy

Stakeholder management

Node.js

TypeScript

React

Education

Computer Science background

Tools

Node.js

TypeScript

React

Job description

London (Hybrid) | Up to £140,000 + Equity

Looking to make a genuine impact at an early-stage AI startup? This is an opportunity to join a well-funded business as one of its first engineering hires, taking ownership of a product already being tested by major enterprise customers.

The Company

This AI startup is building a behavioural intelligence platform that helps financial services organisations better understand customer behaviour and decision-making. Backed by significant early-stage investment, they are working with large enterprise clients and moving from proof-of-concept projects towards commercial deployment. With a small, highly capable team, they are focused on building scalable AI products with real-world impact.

The Role

You will take ownership of product development, helping to build and scale an AI-powered platform from an early stage.

Responsibilities include:

• Building LLM-enabled products and features used by enterprise customers
• Designing and developing backend services, APIs, and platform capabilities
• Owning RAG workflows and AI application architecture
• Managing evaluation frameworks, testing, monitoring, and quality standards
• Optimising LLM performance, scalability, and cost efficiency
• Working closely with product leadership and customers to shape the roadmap
• Establishing engineering best practices across development and deployment

Your Skills & Experience

• Strong experience as a Product Software Engineer
• Proven track record building and shipping an LLM-based product from 0 to 1
• Experience owning architecture, product decisions, and implementation
• Strong backend engineering experience with API-first products
• Hands-on experience with RAG and production AI systems
• Understanding of token usage, model evaluation, and cost optimisation
• Ability to operate autonomously in a startup environment
• Strong communication and stakeholder management skills
• Experience with Node.js, TypeScript, and React
• Computer Science background
• Experience within AI startups, technology companies, or financial services

What They Offer

• Salary up to £140,000
• Meaningful equity package
• Hybrid working in London
• Significant ownership and autonomy
• Opportunity to shape the engineering culture and technical direction
• Direct exposure to founders and business leadership