Bun is a fast, incrementally adoptable all-in-one JavaScript, TypeScript & JSX toolkit. Use individual tools like bun test or bun install in Node.js projects, or adopt the complete stack with a fast JavaScript runtime, bundler, test runner, and package manager built in. Bun aims for 100% Node.js compatibility.
Bun, #2025/12 bought by Anthropic for Claudecode, is a toolkit for js, typescript, jsx. you can use parts of it within node.js. Aims for full compatibility with node.js. Aims for means it doesn't I suppose