Typescript has been moving fast, but they haven't broken that many things. The API and Language Server have changed obviously four times from a semver perspective, but in general the language itself has been extremely stable with great backwards compatibility, and most of the type system strictness additions are behind opt-in flags making upgrades usually as gentle as you prefer them to be (depending on your attitude to strict type checking).

(I had projects that started with TS < 1.0 and they all still parse and compile today, albeit with tons of lint warnings, particularly to use a better module system than AMD with pre-ES2015 TS imports, and all sorts of new type strictness options to turn on to make them all the more type safe.)