Lead Product Reliability Engineer in London

Location: London

Employment Type: Full time

Location Type: Hybrid

Department: Engineering

Compensation: £120K – £170K • £120K – £170K Equity

THE BASICS

This role pays up to £170k/year DOE + equity. Reporting to: Founding Engineer, Josh Harrison. Location: Chancery Lane, London — Mon–Thu in office, Fri WFH.

WHAT ARE WE BUILDING

Fyxer is an AI Email and Meeting Assistant that eliminates admin burden for professionals in client-facing roles. Think sales, consultants, recruiters. We understand your inbox, draft replies in your own voice, and take crisp meeting notes. We're a pure-play applied AI company, not a SaaS product with AI bolted on. We use fine-tuned open-source models, tool use, and retrieval-augmented generation. Users send 53% of the email drafts we generate. Since launching in March 2024, we've grown from $0 to $30M+ ARR. We raised a $10M Series A and a $30M Series B in under 18 months. Our backers include Marc Benioff (Salesforce), Harry Stebbings (20VC), David Singleton (ex-CTO of Stripe), and Madrona (first investors in Amazon and Snowflake).

THE ROLE

We're hiring a Lead Product Reliability Engineer to sit within our platform team, a small, high-ownership group responsible for the infrastructure and services that keep Fyxer running as we scale, including taking ownership for billing, integrations with third-party apps, uptime and incident response. This isn't a ticket-execution role. You'll own the reliability standard for the whole company: what good infrastructure looks like, what it takes to ship safely, and how incidents get resolved and don’t repeat. You'll work across the full stack, from cloud architecture to database migrations, using deep technical knowledge and sound judgement to keep a fast-moving product on solid ground.

Some examples of what the team has achieved in the past months to get a taste:

• Migrated our billing structure in Stripe from a subscription model to usage-based billing, from technical specification through to implementation, with zero downtime.
• Redesigned the entire webhook architecture behind our Outlook integration to completely eliminate rate limiting, changing a core part of the product without any downtime.

WHAT YOU'LL OWN

• Plan and execute infrastructure migrations, the kind where the wrong call takes the product down.
• Be the last line of defence when things break: diagnose it, fix it, and make sure it doesn't happen again.
• Use quantitative data (error logs, cloud metrics) and qualitative data (support tickets, user reports) to identify the highest-leverage reliability improvements.
• Build and maintain the scripts, workflows, and cloud architecture that the product runs on. This is a full-stack engineering role, not just configuration of tools. You'll ship code.
• Work closely with product engineers to review new features before they ship, ensuring they meet the reliability bar before they reach production.
• Own the reliability standard across your product area, so new features and onboardings don’t break what's already working.

WHAT WE'RE LOOKING FOR

The work in this role is what we call crunchy. Feature engineering is creative, there's rarely one right answer. Product reliability engineering is different: there is a right answer, and you need to find it fast, with deep knowledge of how systems behave under pressure.

• Solid TypeScript. Expert level. If you don't have this, you shouldn't apply. You need to be fluent enough to diagnose and fix a production incident fast. In an outage, someone who can't read the code can't help solving the issue.
• Serious cloud experience. Google Cloud or equivalent, at depth. Deployments, scripts, GitHub workflows, operational tasks. The kind of engineer who knows not just how to use a cloud platform but how to architect around its constraints.
• Deep database knowledge. Not just querying, but designing. Understanding the database design options available and how to find the most effective solution, then justifying that against any questions. That’s the kind of problem we solve.
• Production ownership. When something breaks, you’re the one who fixes it. We need someone who’s been in that seat before and knows how to stay calm, move fast, and make sure it doesn't happen again.
• Fullstack capability. You’ll be designing and building features alongside our product engineers, ensuring you support the development of new features from a reliability perspective.
• Genuine obsession with learning. Everyone says this. We mean it differently. The best person for this role goes home and thinks about the problem. They build tools to understand their own gaps. We look for a deep, self-driven obsession with learning and technical craft, and people who get uncomfortable when they stop growing.

WE'RE DELIBERATE ABOUT HIRING

A small team of exceptional people, working hard on a problem they care about, will always beat a larger, less focused team. That intensity means this isn't a normal role, but it also means you'll move faster than anywhere else. Josh Harrison joined as our founding engineer and now leads the platform team you’d be joining. He didn’t come for a well-defined role. He came because the problem was real, the team was exceptional, and the work was genuinely hard. That’s still true. The people who thrive here are the ones who find that combination energising rather than daunting.

Compensation Range: £120K - £170K