About StackOne: StackOne is the AI Integration Gateway for SaaS products and AI Agents. Backed by GV and Workday Ventures ($24M raised), we help builders of SaaS platforms and AI Agents orchestrate hundreds of scalable, accurate, and enterprise-grade integrations. Our platform combines 25,000 pre-mapped actions on 200 connectors, an AI-powered integration development toolkit, plus security by design: a real-time architecture, managed authentication and permissions, and end-to-end observability. Join us on our fast trajectory to build the future of agentic integrations. With an AI-native integration toolkit that delivers real-time execution, managed authentication, granular permissions, and full observability, all built with safety at its core, we’re now doubling down on AI R&D & creating our own lab to push the boundaries of tool calling for agents: training specialized LLMs designed to outperform general-purpose models in what matters most: precision, reliability, and safety in agentic execution. About the role You'll help build a world where users of any agents can integrate with the tool of their choice in one click thanks to StackOne. We are looking for a Software Engineer with a strong background in AI production-grade applications with professional experience working with LLMs (eg: GPT, Anthropic and others). In this role, you will deliver AI features and products end-to-end and work with the wider AI team of StackOne (comprising of AI researchers and other AI engineers). You will report directly to the CTO. Responsibilities Act as a full-stack engineer : design, build, and ship features across frontend, backend, and infrastructure. Leverage AI models to accelerate development, while maintaining best-in-class reliability, testing, and code quality. Build and maintain inference pipelines, embeddings, retrieval, and orchestration systems. Integrate tool-calling and MCP (Model Context Protocol) patterns into product features. Ship and maintain open-source or internal TypeScript/Python packages. Work with AWS and/or Cloudflare to deliver scalable, secure, low-latency systems. Collaborate with product and design to deliver features end-to-end. What we're looking for Proven experience as a full-stack engineer. Expertise in TypeScript and/or Python. Strong background in building on AWS and/or GCP and/or Cloudflare. Experience building and shipping TypeScript/Python packages. Familiarity with tool-calling, agent frameworks, and MCP. Track record of shipping production systems with high code quality and reliability. Curiosity to push the boundaries of what AI-powered development can deliver. Past experience with Generative AI/LLMs and related technologies/frameworks Desire to work in a fast-paced startup, taking ownership of projects e2e and bias towards shipping. (Preferred): Experience working on/publishing CLIs & SDKs Benefits Meaningful share options (EMI) - share in the company's success as we grow 25 days holiday 1 additional day per year of tenure Private health insurance - including dental & optical £15/day lunch budget when working from our London office, up to £120/month £1,000 for your home office set up £500/year top-up Annual team offsite to sunny spots (last ones were in Spain and Portugal ☀️) Join one of Europe’s fastest-growing startups Work with a veteran team of ex-employees of Google, Microsoft, Oracle, Coinbase, JP Morgan and more Health, fitness and gift card discounts Cycle2Work and Electric Cars scheme Hybrid working friendly - typically 2 days/week in our London office. We’re open to discussing flexible arrangements—please share any preferences in your application Ready to help us change the game for SaaS integrations? Get in touch and let's chat! We believe diversity drives innovation. We encourage individuals from all backgrounds to apply. As an equal-opportunity employer, we celebrate diversity and are committed to creating an inclusive environment for all employees.