TypeScript 6.0 Ships Its Own Obituary

TypeScript 6.0 landed on March 23, and if you upgrade without reading the changelog, your CI will break. Not "might break" — will. The new defaults flip strict to true, target to ES2025, and moduleResolution to bundler. If your tsconfig relies on inherited defaults (most do), you're in for a morning of red squiggles.

But the defaults are just the surface. This release is really about one thing: clearing the runway for TypeScript 7.0, the Go-native rewrite that promises dramatically faster builds through parallel type checking. TypeScript 6.0 is the last version built on JavaScript, and it knows it. Every deprecation in this release is a feature that won't survive the port.

#Every default just moved

Here's what changed if you don't set these explicitly:

The types: [] change is the sneakiest. If you're not explicitly listing "types": ["node"] in your tsconfig, you'll get "Cannot find name 'process'" errors the moment you upgrade. TypeScript no longer auto-discovers @types packages from node_modules.

The rootDir change is the one that'll confuse you most. Files that compiled to dist/index.js now land at dist/src/index.js because the compiler defaults to the config file's directory instead of inferring from your source tree. Fix both immediately:

{
  "compilerOptions": {
    "types": ["node"],
    "rootDir": "./src"
  }
}

#Fourteen deprecations, one message

The list is long, but the message is simple: if it doesn't work in Go, it's gone.

The big ones:

• target: es5 — Lowest target is now ES2015. Still shipping ES5? You need a separate transpiler.

• --moduleResolution node (a.k.a. node10) — Use nodenext or bundler.

• --moduleResolution classic — Removed entirely. Nobody's used it since 2018.

• --outFile — Use a real bundler.

• --baseUrl — Inline the values into your paths entries.

• module Foo {} syntax — It's namespace Foo {}. Has been for years. This enforces it.

• Import assertions — import ... assert {} becomes import ... with {}.

You can buy time with "ignoreDeprecations": "6.0" in tsconfig. This suppresses warnings and keeps everything working. But TypeScript 7.0 hard-removes these options. No escape hatch.

#The import syntax shift

With esModuleInterop defaulting to true, the old CommonJS interop pattern changes:

// Before (esModuleInterop: false)
import * as express from "express";
import * as React from "react";

// After (now the default)
import express from "express";
import React from "react";

Both forms still compile. But the namespace import pattern will feel increasingly like dead code in new projects.

#Fix your path aliases

If you used baseUrl to set up path aliases, inline the base into each path entry:

// Before (5.x)
{
  "compilerOptions": {
    "baseUrl": "./src",
    "paths": { "@app/*": ["app/*"], "@lib/*": ["lib/*"] }
  }
}

// After (6.0+)
{
  "compilerOptions": {
    "paths": { "@app/*": ["./src/app/*"], "@lib/*": ["./src/lib/*"] }
  }
}

Or skip the manual work — ts5to6 handles this automatically:

npx ts5to6 --baseUrl   # fixes baseUrl + paths
npx ts5to6 --rootDir   # fixes rootDir inference

Handles monorepos and tsconfig inheritance chains too.

#One flag worth knowing about

--stableTypeOrdering is a new flag that forces the compiler to produce union types in a deterministic order matching TypeScript 7.0's Go-based output. Useful for diffing .d.ts files between versions during migration testing.

The catch: ~25% performance hit. Use it to validate, then remove it.

#What's actually coming

TypeScript 7.0 is reportedly close to completion. The Go rewrite enables parallel type checking and shared-memory multithreading — the kind of gains that make a 100k-line codebase feel like a 10k-line one.

The play: upgrade to 6.0 now, fix every deprecation warning, run ts5to6 on your configs, and you'll be ready when the native compiler drops. Ignore the warnings and you're looking at a forced migration later — one without ignoreDeprecations to soften the landing.