The Solid Design System started as a visionary initiative and has now become an indispensable part of Union Investment's digital strategy. As an integral part of the design system team, we have been responsible for design-side engineering, stakeholder management, consumer support, and enablement for over four years. As an enterprise-wide delivery platform and AI enabler, the Solid Design System provides a shared foundation for multiple brands, product teams, and AI agents. Through multi-theming, the Solid Design System serves not only Union Investment but also partner banks such as Volksbanken and Sparda-Bank. Colors, icons, and assets switch via themes while components and code remain the same—ensuring every customer journey is seamless. At the same time, Solid provides the infrastructure for agentic workflows. A dedicated MCP server, Code Connect, and machine-readable descriptions, guidelines, and tokens give AI agents the necessary context. They design in Figma, build prototypes, and write code using real Solid components rather than inventing their own—on-brand, accessible, and production-ready.