Steffen Schroeder updated the TypeScript type definitions for Sinon.js in the DefinitelyTyped/DefinitelyTyped repository, focusing on compatibility with Sinon versions 20 and 21. He removed deprecated properties and methods to align the typings with recent Sinon releases, thereby reducing type noise and preventing type-related issues for downstream projects. His work centered on improving type safety and the overall developer experience for TypeScript users who rely on Sinon for testing. By leveraging his expertise in TypeScript, type definitions, and testing, Steffen ensured that the updated typings accurately reflected the evolving Sinon API and maintained consistency across the TypeScript ecosystem.