Lead Product Reliability Engineer

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. 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.

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:

• 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.
• Serious cloud experience. Google Cloud or equivalent, at depth. Deployments, scripts, GitHub workflows, operational tasks.
• Deep database knowledge. Not just querying, but designing.
• Production ownership. When something breaks, you’re the one who fixes it.
• Fullstack capability. You’ll be designing and building features alongside our product engineers.
• Genuine obsession with learning.

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.