Let’s look into the improvements and the new features that come with upgrading to Angular 4. According to the semvar specification, major upgrades come with API changes that may be incompatible with legacy versions of the API. These API changes can be a large source of concern for developers worried about deprecated features causing their app to stop working as expected. Thankfully, another huge strategy change with Angular 4 from 2 was a much more predictable & reliable upgrade experience for developers.