TypeScript 6.0 RC Marks the Final JavaScript-Based Release as Microsoft Prepares Go-Powered Rewrite
Microsoft ships the final JavaScript-based TypeScript release, overhauling defaults and deprecating legacy options ahead of a Go-powered compiler rewrite in version 7.0.
Microsoft published the TypeScript 6.0 Release Candidate on March 6, a milestone the team calls unique in the language’s history. “TypeScript 6.0 is a unique release in that we intend for it to be the last release based on the current JavaScript codebase,” wrote Daniel Rosenwasser, TypeScript’s principal product manager, in the announcement.
The RC arrives as TypeScript sits at the peak of its influence. GitHub’s latest Octoverse data show that TypeScript overtook both Python and JavaScript to become the platform’s most-used language in August 2025, adding more than one million contributors in a single year.
Stricter defaults, fewer legacy options
The headline changes in 6.0 are not new language features but a broad tightening of the compiler’s default behavior. Strict mode is now enabled by default, the module system defaults to esnext rather than commonjs, and the compilation target moves to es2025. The types field defaults to an empty array, which means projects must explicitly declare their type dependencies instead of automatically pulling in every installed @types package.
Several long-deprecated options are formally removed. ES5 as a compilation target is gone, along with AMD, UMD, and SystemJS module formats. The baseUrl configuration option, --outFile bundling, and the legacy --moduleResolution node setting are all deprecated. Projects that still depend on these can set "ignoreDeprecations": "6.0" as a temporary escape hatch, but that flag will not carry forward into TypeScript 7.0.
New capabilities
Alongside the deprecations, 6.0 adds ES2025 support including the RegExp.escape() method, Temporal API types, and new Map and WeakMap upsert methods (getOrInsert() and getOrInsertComputed()). The compiler now supports Node.js subpath imports starting with #/, aligning with bundler conventions, and permits the previously-forbidden combination of --moduleResolution bundler with --module commonjs to ease migration paths.
A new --stableTypeOrdering flag lets developers opt into TypeScript 7.0’s deterministic type ordering ahead of the migration, though the team warns it can add up to 25 percent overhead to type-checking time.
The Go rewrite on the horizon
The strategic rationale behind 6.0’s aggressive cleanup is TypeScript 7.0, a ground-up rewrite of the compiler in Go. The new codebase will take advantage of native code speed and shared-memory multi-threading to address compilation bottlenecks that have grown acute in large monorepo environments where build times can stretch into minutes.
Microsoft has already shipped native preview builds under the @typescript/native-preview npm package and a companion VS Code extension. TypeScript 6.0 is designed as the bridge: by removing legacy surface area now, the team narrows the behavioral gap between the JavaScript and Go implementations and gives the ecosystem time to adapt before 7.0 lands.
Migration path
The team recommends that projects begin migration immediately. An experimental ts5to6 codemod is available to automate common configuration changes. The most impactful adjustments for most teams will be explicitly setting the types array, replacing baseUrl with fully-qualified paths entries, and moving from --moduleResolution node to nodenext or bundler. Microsoft says projects that properly configure the types array can expect 20 to 50 percent build time improvements even before the native compiler arrives.