How did we get to Drupal 9?

Drupal 9 does not represent a great milestone in the traditional sense. It does, but not one comparable in scale to the release of Drupal 8.0 when the entire world cheered and the stock markets rallied. Rather, Drupal 9 represents proof that some decisions were made wisely when the time came to change the release approach Drupal was accustomed to.

Before Drupal 8, every few years a major version of Drupal was released. And with these releases came the joy of getting all the new features and leaving the old behind. But what also came was the pain of upgrading to these new releases. No more, said Drupal 8, which has been steadily introducing new features and functionality with each minor release until now. To the point that we have reached the end of the Drupal 8 release cycle and have gone into Drupal 9 in almost the same way as we've been going from one minor release to another, say, from 8.5 to 8.6. But then what is the difference?

In semantic...