Senior Backend Product Engineer

ZipRecruiter; London; On-site; GBP 120,000 - 170,000; Full time

Job summary

A leading AI startup in the UK is seeking a Senior Backend Product Engineer to join their London team. This role involves designing backend systems to optimize productivity tools for professionals, ensuring seamless integration with external APIs. Ideal candidates will have substantial experience in backend development, a strong grasp of TypeScript, and a passion for AI technologies.

Benefits

Equity

Private healthcare

Work in-person with an elite founding team

Huge ownership and autonomy

Qualifications

• 5+ years experience as backend engineer in a startup or high-growth environment.
• Expert-level fluency in TypeScript.
• Experience with scalable systems in the cloud.

Responsibilities

• Design and scale backend infrastructure for millions of user actions.
• Own integrations with APIs and collaborate on product direction.
• Drive performance and reliability across cloud services.

Skills

TypeScript

Google Cloud Platform

SQL

CI/CD

AI

Tools

GitHub Actions

BigQuery

Job description

Job Description

We are thrilled to be partnering exclusively with Fyxer AI - the fastest growing AI start-up in the UK - to recruit talented Senior Backend Product Engineers for their London team.

What Are They Building?

Great people are working on overdrive to do a great job but are held back because their inbox is failing them. Fyxer AI is building an AI productivity tool that eliminates admin for client-facing professionals: consultants, recruiters, real estate agents anyone drowning in emails, scheduling, and follow-ups. Fyxer AI drafts emails in your voice, takes crisp meeting notes, and auto-manages your inbox.

How’s It Going?

Since launching in May 2024, they've grown from $0 to $10M+ ARR with thousands of paying users. In Feb 2025, they raised a $10M Series A backed by top-tier investors including Marc Benioff (Salesforce) and 20VC.

They spent Q4 2024 at HF0 in San Francisco, the top AI startup accelerator, learning from legends like the CEO of Instacart and the Head of Applied Research at OpenAI.

They are now entering hypergrowth and building the engineering team that will scale them to $50M+ in revenue.

What They Value

Small teams. Big ownership. High talent density.

They don’t hire for headcount. They hire people who ship, who care, and who think from first principles.

At Fyxer, "Product Engineer" means you’re not just writing backend endpoints you’re building products. You’ll look at usage data, talk to customers, and design elegant solutions with real impact.

What You’ll Be Doing

You’ll work closely with Matt (CTO) and the engineering team to scale and evolve their backend systems as they grow to tens of thousands of users.

Expect to own high-leverage features across everything from core architecture to AI workflows to observability.

Some things you’ll work on:

• Design and scale backend infrastructure to handle millions of user actions per day
• Build real-time processing pipelines for email, calendar, and Zoom data
• Own integrations with external APIs (Google, Microsoft, OpenAI)
• Collaborate on product direction, usage insights, and user experience
• Drive performance, reliability, and observability across our cloud functions and services
• Make key decisions around architecture, data modelling, and tooling

Ideal Candidate

• 5+ years experience working as a backend engineer in a startup or high-growth environment
• Expert-level fluency in TypeScript, including server-side development
• Solid experience with Google Cloud Platform or similar (e.g. AWS, Azure)
• Built scalable systems using Cloud Functions, PubSub, Firestore, Cloud Storage, etc
• Confident writing SQL (BigQuery or equivalent) and building data flows that scale
• Comfortable owning infrastructure and CI/CD (we use GitHub Actions + GCP)
• Product mindset you care about what you're building and why it matters
• Experience with AI or high interest in AI-powered productivity tools would be ideal
• Intensity, urgency, and high standards for your work

Our Tech Stack

• TypeScript across the stack
• React frontend, but the product is backend-heavy
• Google Cloud Platform: Cloud Functions, Firestore, Cloud Storage, PubSub
• BigQuery, Looker, Sentry, Google Cloud Logging
• CI/CD via GitHub Actions

What You’ll Get

• £120K-£170K + equity
• Huge ownership and autonomy from day one
• Private healthcare
• Work in-person with an elite founding team (Oxford, HF0, backed by world-class investors)
• A chance to build category-defining tech that people actually use
• Early-stage speed with the scale and traction of a growth company

***This role is based in Chancery Lane, London 4 days-per week. We are looking for candidates who value in-person collaboration.***