Microsoft Open-Sources Rayfin, an SDK/CLI to Define Full App Backends in Code and Deploy to Fabric

The New Stack·medium signal

At Build 2026 Microsoft introduced Rayfin, an open-source SDK and CLI that lets developers and coding agents define an application backend — data models, business logic, auth, and access policies — entirely in code, then deploy it to Microsoft Fabric. It's aimed at making backends agent-authorable end to end. The move pushes Microsoft's agent tooling beyond the IDE into deployable infrastructure.