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TypeScript 7 Migration at Scale: The Parity Ladder for Moving Many Teams to the Native Compiler
The compiler swap is the easy part. The hard part is the months when your editor, linter and CI run different TypeScripts.
TypeScript 7 makes type checking roughly ten times faster.
For one repo, that is a dependency bump. For an org with fifty repos and a shared lint config, it starts a period where two compilers decide what “valid” means, and they don’t always agree.
This article is about that period. If you own frontend tooling for more than a handful of teams, a TypeScript 7 migration is a platform migration, and I’d plan it the way you’d plan a runtime upgrade: with an inventory, a shadow phase, a parity gate, and an exit date for the old version.
The decision in one paragraph
Most teams will treat TypeScript 7 as a version bump that each team does when it gets around to it. I think that is the wrong unit of work. For the next few months, many repos will run two TypeScripts at once: the native 7.x tsc in CI, and a 6.x compiler behind anything that imports typescript as a library. Your code will mostly be fine. The real risk in that setup is drift: the editor, the linter and CI…
