Senior Product Engineer

Harnham - Data and Analytics Recruitment; Greater London; On-site; GBP 120,000 - 140,000; Full time

Benefits offered by this job

Equity

Hybrid working

Exposure to founders

Job summary

Harnham - Data and Analytics Recruitment in London seeks a Senior Product Engineer to own an AI-powered platform currently tested by major enterprise customers. The role offers hybrid work and a meaningful equity package.

You will build LLM-enabled features, own architecture, and collaborate with leadership to shape the product roadmap. A strong backend and API-first approach are essential in this fast-growing startup.

Qualifications

• Experience shipping an LLM-based product from 0 to 1.
• Owns architecture and product decisions.
• Strong backend with API-first design.

Responsibilities

• Build and scale an AI-powered platform for enterprise customers.
• Design and develop backend services, APIs, and platform capabilities.
• Own RAG workflows and AI application architecture.
• Manage evaluation, testing, monitoring, and quality standards.
• Optimize LLM performance, scalability, and cost efficiency.
• Collaborate with product leadership and customers on roadmap.
• Establish engineering best practices for development and deployment.

Skills

Product Software Engineer

LLM-based product

Backend engineering

Architectural ownership

Stakeholder management

Education

Computer Science background

Tools

Node.js

TypeScript

React

Job description

Senior Product Engineer

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

Desirable:

• 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