The Drupal Association runs the Project Analysis job every week to help the community assess the readiness of contributed projects to upcoming major versions. Before the release of Drupal 9, I worked with Ryan Aslett at the Drupal Association to fine-tune this job and built an easy to browse data dashboard that helps to make sense of the raw results (not live anymore for Drupal 9). For Drupal 10, I worked with Björn Brala (Technical Director of Swis) to modernize the infrastructure of the job and updated the readiness dashboard to be even more detailed and functional.
Running deprecation checking tools on all contributed projects allowed us to inform Palantir.net's funding prioritisation for Drupal Rector automation, help focus contribution events, such as the most recent porting days in November and even to build the Project Update Bot. It was also used by Acquia's DIT team to contribute significantly to porting many of the high profile projects our customers are using.
Now that we have the historic data, we can also compare how contributed projects did when Drupal 9 was released and how ready is the ecosystem for Drupal 10 now. At the time of the Drupal 10 beta release, in his Driesnote at DrupalCon Prague, project lead Dries Buytaert said there were three times as many projects ready (in development versions) as there were for Drupal 9 at the comparable time.
Comparing the two timelines, Drupal 9 contributed project's readiness trajectory is catching up to Drupal 10's, but the new version is still well ahead of Drupal 9 at release with 26% more projects being ready (at least in development versions) compared to Drupal 9. This is how the comparison looks like with a moving average drawn for both:
While this makes Drupal 10 the easiest major version to upgrade to in a decade, it is not all about the stats of course. You are welcome to dive right into the readiness data for Drupal 10 projects. I posted in April about the goodies on our dashboard new to the Drupal 10 edition.
I also maintain the Upgrade Status project which provides you with a site-tailored readiness assessment about the hosting environment as well as about every single Drupal extension used.