TypeScript 7 Beta (tsgo): What Broke in My Real Monorepo

Two notes on honesty. The CI number is diluted by checkout and dependency install, which tsgo cannot help with, so the job-level win is 3.4x rather than 7.7x. And the editor number changed how I work more than any other row: at 0.6 seconds in watch mode, type-checking moved out of CI and back into my inner loop. I had stopped running the checker locally because 71 seconds was long enough to context-switch away from. Now it runs on every save.

What actually broke when I switched?

Five things broke: a language-service plugin, a ts-patch transformer, api-extractor, mixed incremental caches, and ts-node. Zero type errors changed. Across 161k lines, tsgo produced the identical diagnostic set to tsc, byte for byte after sorting. The compiler kept its promise. The ecosystem around it did not.

The CSS modules language-service plugin stopped loading

I use typescript-plugin-css-modules for class-name completions in .module.css imports. The beta's language server does not load classic tsserver plugins, so the "plugins" entry in tsconfig is ignored and completions silently disappear. Workaround: I added a typed-css-modules codegen step that emits committed .d.ts files, which works under both compilers.

My ts-patch transformer was silently skipped

The Express API used a ts-patch transformer to generate route metadata at compile time. tsgo has no JavaScript transformer hook, so the build succeeded but the metadata object was missing, and the first request crashed with TypeError: Cannot read properties of undefined (reading 'routes'). Workaround: I moved the generation into a standalone codegen script that runs before the build. tsgo now checks with --noEmit and esbuild handles emit.

Compiler-API tools still need tsc installed

api-extractor and typedoc import the typescript package's JavaScript API. tsgo is a native binary with no compatible API surface, so pointing them at the preview package fails immediately with errors like TypeError: ts.createProgram is not a function. Workaround: keep typescript@6 installed as a devDependency purely for those tools. They run on tsc while every check runs on tsgo. Same answer applies to ts-morph if you use it.

Mixed .tsbuildinfo caches broke incremental --build

tsgo writes its own incremental state format. When my CI cache restored .tsbuildinfo files written by tsc, tsgo discarded them and re-checked the entire graph every run, which quietly erased most of the CI win for a week before I noticed. Workaround: set a distinct tsBuildInfoFile path per compiler, or bump your CI cache key when you switch.

ts-node drifted from the checker

Maintenance scripts ran under ts-node, which type-checks at runtime using whatever typescript package it resolves. After I removed TypeScript 6 from one workspace, those scripts crashed on startup. Workaround: I moved the scripts to tsx, which transpiles without checking. tsgo already checks everything in CI, so runtime checking was redundant anyway.

The compiler was the safest part of this migration. Everything that bit me was a tool standing next to the compiler, not the compiler itself.

How do I audit my own repo before switching?

Run a fifteen-minute audit before installing anything: inventory tsserver plugins, transformers, compiler-API tools, and runtime TypeScript execution, then diff diagnostics between both compilers. Here is the table I now run against every repo I touch:

Then roll out in this order:

1. Install the preview alongside tsc, never as a replacement: npm i -D @typescript/native-preview@beta.


2. Diff the diagnostics. Run both compilers with --noEmit and compare sorted output. Mine matched exactly.


3. Add tsgo as a parallel, non-blocking CI job and let it run for a week of real commits.


4. Flip the required gate to tsgo, and keep a nightly tsc run as a fallback gate until stable ships.


5. Switch your editor last. The language server is the least mature surface in the beta.