Lead Engineer

ImmigrationGPT; Greater London; Hybrid; GBP 100,000 - 170,000; Full time

Benefits offered by this job

Pension, matching contributions

Private Medical Insurance

Juno Wellbeing Credits

Hybrid Working (London)

£150 Home Office Setup Budget

Night Key Membership

Birthday Leave

Learning & Development Budget

Job summary

Buttermilk Limited in London is hiring a Lead Engineer to own the Pantry platform. You will shape architecture, scale systems to handle thousands of users and partner with product and data teams to deliver AI-powered campaigns end-to-end.

You will engineer production features, ensure observability, and drive cross-functional collaboration in a hybrid London-based role.

Qualifications

• Built and scaled a production product to 10,000+ users and made architecture calls.
• Ships vertical slices quickly, without overbuilding for a month ahead.
• Experience shipping LLM features to production with structured output and cost per item.
• Authenticated data isolation between clients and GDPR-compliant design.
• Able to explain trade-offs clearly to non-engineers.

Responsibilities

• Own architecture and scaling decisions for the Pantry platform.
• Develop and ship production features with AI tooling.
• Ensure observability, monitoring and reliability in production.
• Collaborate with product, data science and engineering teams.

Skills

Production scaling

AI coding tools

LLM features

Authentication

Data isolation

SOC 2

Python

FastAPI

Terraform

Google Cloud

Tools

Python

FastAPI

Next.js

TypeScript

Google Cloud

Terraform

Cloud Run

Cloud SQL Postgres

BigQuery

Pub/Sub

Job description

# Lead EngineerButtermilk Limited, LondonApply on Buttermilk Limited's site Check my CV against this jobPosted: 5 days agoContract: permanentListed on: Direct from the employer## Can this job be sponsored?Some things to check* We could not tell the occupation from the title. Whether a job can be sponsored depends on its occupation code. Look up the occupation code (CASCOT)* Buttermilk Limited holds an A-rated Skilled Worker licence. Register of licensed sponsors, GOV.UKRead from the advert, the Home Office register and the Immigration Rules. Whether you can be sponsored also depends on your own circumstances, such as your age and visa history. This is information, not advice.## About the jobLead EngineerLondonPermanentHybrid Working - 3 days in the office, 2 days remoteWe run the campaigns ourselves, so we know exactly what the software has to do.Buttermilk is a London creator-marketing agency. Pantry is the platform our team, our creators and our clients use to run campaigns end to end. It is live with our internal team today. The demand is already here: every campaign we run is waiting on this platform.Why this is differentSearch and reporting are table stakes. The hard part is the operational core: shortlists clients actually approve, outreach that lands, creators paid on time, and AI that understands the Creator.Most creator platforms are built by people who have never run a campaign. Ours is built next to the team that runs them every day.What you'd ownThe platform that takes Pantry from alpha to what the whole agency runs on. If you want to point at a platform in production and say you built it, this is that seat.You code every day, set the architecture and work as the product partner to Matt, our Product Lead.- Build. Ship vertical slices that real users can try, quickly but built to last. Direct AI coding agents and review their output critically.- Decide. Own the architecture and scaling calls, and keep one source of truth for how the system fits together.- Run it. Own observability and alerting, and step in when production misbehaves.- Partner on product. Break epics into stories, flag dependencies early, challenge the roadmap and demo to the business.- Plan honestly. Say what one engineer can deliver by a given date, and say early when that is not enough.- Grow the team. Decide when we need more engineers, then hire and lead them.Along the way: the production basics, creator and campaign intelligence with our data science lead, and integrations for CRM, payments, outreach and invoicing, on a path to SOC 2.The team you'd join- Product Lead- Full Stack Engineer- Data Science Lead- The campaign team: our daily users, at the next desk.How we workDecisions are written down and shipped, not held in meetings. We build agent-first and test-driven, in small pull requests, with everything in code, infrastructure included.What we're looking forWe are hiring at lead level, to build and to stay. There is no senior engineer above you.- You have built and scaled a production product to 10,000+ users, and made its architecture calls- You ship in vertical slices, fast but without building things that fall over a month later- You use AI coding tools every day, can refactor a largely agent-written codebase, and read what the agents produce- You have shipped LLM features to production, not just prototypes: structured output, validation, batch versus live calls, cost per item and evaluation- You have built for external users: authentication, data isolation between clients, payments and GDPR- You build rapport quickly with non-engineers and explain trade-offs plainly- You like being in the office with the people who use what you buildStrong plus: multimodal AI (video, image, audio); Python and FastAPI; Google Cloud, Terraform and CI/CD; ingestion from third-party APIs; email deliverability; SOC 2; creator-economy or agency experience.Transferable experience counts. If your architecture and scaling experience carries over, the exact stack matters less.You probably won't enjoy this if- You want detailed specs before you start- You would rather design systems than build and run them- You want a specialist for every layer- You trust AI-written code without reading itStackPython services (FastAPI, SQLModel) and a Next.js/TypeScript app on Google Cloud: Cloud Run, Cloud SQL Postgres, BigQuery and Pub/Sub, all in Terraform and deployed from GitHub Actions. It's early enough that you will shape it.What We Offer- Pension, matching contributions- Private Medical Insurance- Juno Wellbeing Credits- Hybrid Working (London)- £150 Home Office Setup Budget- Night Key Membership- Birthday Leave- Learning & Development Budget