TypeScript 6 is Released

https://devblogs.microsoft.com/typescript/announcing-typescript-6-0/

Why This Matters

TypeScript 6.0, released March 23, 2026, is the final release built on the JavaScript codebase. After this, the compiler moves to Go with TypeScript 7.0 (codenamed "Corsa"). This is a deliberate bridge release -- it introduces aggressive breaking changes and deprecations now so the ecosystem can prepare before 7.0 removes them entirely.

The Big Picture

TypeScript 6.0 is a cleanup release. The native Go-based TypeScript 7.0 is "extremely close to completion" and expected within months. The 7.0 benchmarks are dramatic:

Project	TS 5.x/6.x	Native 7.0	Speedup
VS Code (1.5M lines)	77.8s	7.5s	10.4x
Playwright (356K lines)	11.1s	1.1s	10.1x
TypeORM (270K lines)	17.5s	1.3s	13.5x

Editor loading for VS Code drops from 9.6 seconds to ~1.2 seconds. Memory usage roughly halves.

Key Breaking Changes

New defaults that will surprise you:

strict: true (was false)
module: esnext (was commonjs)
target: es2025 (floating to current-year ES version)
types: [] (was auto-enumerated from node_modules/@types -- this alone can improve build times 20-50%)

Removed or deprecated:

target: es5 -- deprecated; ES2015 is now the minimum
--moduleResolution node -- must migrate to nodenext or bundler
--moduleResolution classic -- removed entirely
--module amd/umd/systemjs/none -- removed
--outFile -- removed; use external bundlers
esModuleInterop: false -- can no longer be disabled
--baseUrl as module resolution root -- deprecated

Escape hatch: "ignoreDeprecations": "6.0" in tsconfig suppresses deprecation errors, but provides no path forward for 7.0.

New Features

Temporal API types now included in built-in type libraries
es2025 target with RegExp.escape support
Subpath imports with #/ prefix (Node.js #/* patterns)
--stableTypeOrdering flag for validating code against 7.0's parallel type-checker behavior
DOM iteration types consolidated into base lib.dom

Our Experience

We attempted upgrading to TypeScript 6 as part of our Astro 6 site dependency upgrade on 2026-03-30. We had to revert -- the Astro toolchain (tsconfck, @astrojs/check, svelte2tsx) all still require TypeScript 5.x via peer dependencies. This is typical for early weeks after a major TS release. We'll revisit once the ecosystem catches up.

What To Watch

TypeScript 7.0 (native Go port) release timeline
Astro and Svelte tooling support for TS 6
Whether the types: [] default causes widespread CI breakage across the ecosystem
Preview builds of 7.0 available via @typescript/native-preview npm package