Backend Software Engineer

• Location:
  
  UK, remote with occasional travel

In the words of one of our senior clients recently…

"Market Research has changed more in the past 3 years, than in the previous 40"

System1 is The Creative Effectiveness Platform. Our target customers are the world's largest advertisers. We predict and improve marketing effectiveness. Our advertising and idea tests measure emotion to give our customers the most accurate predictions of the business impact of creativity.

To learn more about us, please visit System1 Group | Create with Confidence

We are looking for a talented and ambitious Backend Software Engineer to join the empowered product team building System1's next-generation AI platform. You will help shape how the world's largest brands predict and improve the effectiveness of their advertising, building the Python services, APIs and integrations that power the platform. You will work as a first-class member of the product team alongside your Product Manager, Product Designer and Team Lead to discover and deliver outcomes that matter to our customers and our business.

This is a rare opportunity to help build a new platform from the ground up, engineer in a genuinely AI-native way, and work at the speed our market demands.

• Are you energised by being a true partner in the product team, helping decide what to build, not just how to build it?

• Do you already engineer through Claude Code every day, with your own skills and subagents, and the discipline to own every line you ship?

• Are you motivated by outcomes over outputs, and by getting production systems working at scale rather than shipping features for their own sake?

Do you want to join us to excite and change the industry?

• Partner as a member of an empowered product team (Product Manager, Product Designer, Team Lead and engineers), sharing accountability for the outcomes your team commits to.

• Contribute to continuous product discovery, helping the team assess feasibility early and building quick technical prototypes to test ideas before we commit to building.

• Design, build and own Python backend services for our AI platform, from media upload through asynchronous ML processing to insight delivery.

• Work API-first and spec-driven, defining clean REST contracts that serve headless frontends, internal teams and customer integrations.

• Build MCP servers that make System1's data and capabilities available to AI agents and tools, for customers and colleagues alike.

• Engineer through Claude Code day to day, building and sharing skills, subagents and workflows that raise the speed and quality of the whole team.

• Take code into production at scale with confidence, bringing the testing, observability and reliability our enterprise customers expect.

• Contribute to our infrastructure as code and cloud environment, understanding how your services are deployed, run and scaled.

• Work alongside our data scientists to bring models into production, learning the machine learning side of the platform as you go.

• Build with enterprise security and compliance in mind, so the world's largest advertisers can trust the platform with their data.

• A missionary, not a mercenary. You care deeply about the customer problem and the outcome, not just the code.

• Outcome-driven. You measure your success by the change you create for customers and the business, not by tickets closed.

• An engineer first, with AI as a force multiplier. You use AI tools to move faster with rigour, not to skip the thinking.

• Comfortable with ambiguity and ownership. You don’t wait for a perfectly specified ticket, you frame the problem with your team and go.

• A clear communicator, able to explain technical…