Senior UI Systems Engineer - AI SaaS

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2Posted:

26.08.2025Expiry Date:

10.10.2025col-wideJob Description:

Shape the design system behind a unicorn AI-native SaaS platform, scaling globally at speed.Why This Role?Stax

is partnering with a

unicorn AI-native SaaS scale-up

that’s transforming how organisations use AI. Since 2020 they’ve:Grown rapidly to a

global teamRaised

$100M+ in Series A fundingReached

unicorn status with a $1.1B valuationNow they’re building a

London engineering hub . Join as a UK

founding engineer -

hybrid working, high impact, and the chance to shape a

category-defining platform

from day one.The OpportunityThis is a systems-level role at the intersection of design and engineering.

You’ll be at the heart of a platform that’s changing how organisations use AI for customer support and product operations.In just four years, the team has:Open-sourced client-side analytics

on DuckDB, bringing OLAP to the edgeBuilt AI-native UIs

that feel fast, intelligent, and funScaled a themeable design system

adopted across multiple products and platformsIntroduced micro-frontends

that power independent, high-velocity teams—and let customers embed their own modules directly in the productDelivered deeply configurable UIs

where layouts, components, and visualisations can be reshaped end-to-end via declarative configYour role: define the system that makes every pixel seamless, scalable, and lightning-fast.What You’ll DoEvolve the design system: tokens, theming, accessibility, visual languageBuild React + Web Component libraries for core + embedded appsAdvance tooling: Storybook, Chromatic, Figma pluginsSet standards and governance across design + engineeringDeliver performant layouts and visualisations at scaleMentor peers on accessibility and performance-first developmentTech Ecosystem You’ll ShapeWhat You Bring8+ years in large-scale web apps, 2+ in design-system architectureStrong perspective on tokens, theming, multi-brand supportMastery of React + TypeScript, with library publishing experienceAccessibility leadership (WCAG, ARIA, keyboard nav, colour contrast)Fluency in CSS methodologies and testing frameworksExcellent communication skills to align design, product, and engineeringBonus points

for OSS contributions, Figma plugins, or micro-frontend orchestrationCulture and ImpactSpeed with craftsmanship : fast feedback, continuous delivery, peer reviewsPerformance-first mindset : Core Web Vitals as product metricsInclusive and global : teams across the US, Europe, and IndiaAutonomy with accountability : design, guide, measure, iterateLondon hub : hybrid model, build the team and culture from the ground upYour design system will power products used by some of the world’s most ambitious teams. Join at a moment of hyper-growth and play a defining role in one of the most exciting SaaS platforms in the world.? Apply today or reach out directly to

Stax

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