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To install the TypeScript definitions for Bun’s built-in APIs, install @types/bun. 
bun add -d @types/bun # dev dependency
At this point, you should be able to reference the Bun global in your TypeScript files without seeing errors in your editor. 
console.log(Bun.version);

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Suggested compilerOptions

Bun supports things like top-level await, JSX, and extensioned .ts imports, which TypeScript doesn’t allow by default. Below is a set of recommended compilerOptions for a Bun project, so you can use these features without seeing compiler warnings from TypeScript. 
{
	"compilerOptions": {
		// Environment setup & latest features
		"lib": ["ESNext"],
		"target": "ESNext",
		"module": "Preserve",
		"moduleDetection": "force",
		"jsx": "react-jsx",
		"allowJs": true,

		// Bundler mode
		"moduleResolution": "bundler",
		"allowImportingTsExtensions": true,
		"verbatimModuleSyntax": true,
		"noEmit": true,

		// Best practices
		"strict": true,
		"skipLibCheck": true,
		"noFallthroughCasesInSwitch": true,
		"noUncheckedIndexedAccess": true,
		"noImplicitOverride": true,

		// Some stricter flags (disabled by default)
		"noUnusedLocals": false,
		"noUnusedParameters": false,
		"noPropertyAccessFromIndexSignature": false,
	},
}
If you run bun init in a new directory, this tsconfig.json will be generated for you. (The stricter flags are disabled by default.) 
bun init