The parallel development of the new language server and extension ensured that by late 2025 it was possible for VS Code development to shift to TypeScript 7, with TypeScript 6 used as a fallback if there were any issues. Those cases could then be reported back to the TypeScript team and used to prioritize development.
As the platform evolved, the use cases for the VS Code team changed. By early 2026 TypeScript 7 was stable and nearly feature-complete, so the team began to use it to build all of their own built-in extensions. This allowed them to rethink their toolchain, changing the bundler from webpack to the one built into esbuild, giving them another speed up. Once that process was tested and working, they could switch all development to TypeScript 7.
Having such a big project take on TypeScript 7 early reaped big rewards, as the resulting virtuous cycle allowed both VS Code and TypeScript to move forward together, fixing issues as they arose and providing valuable feedback. The results speak for themselves. Type checking the entire VS Code codebase is now 7x faster, with most extensions checked in under a second. The only exception was GitHub Copilot, which is almost as big as the editor itself, which type checked in 2.5 seconds.
