November 1, 2021
Convert a Standard Drupal 8 Site to a Composer Managed Site - Upgrade a standard Drupal 8 site, by converting it to a Composer-managed Drupal 8 site on the new Integrated Composer framework. The documentation provides a guide for converting a standard Drupal 8 site using drops-8 to the new Integrated Composer drupal9 upstream while remaining on Drupal 8.
Using Solr 8 on Drupal 9 - Pantheon Search with Solr 8 is currently in Limited Availability. Pantheon Search derives from Apache Solr 8 and gives Drupal 9 web teams a high-performance search index integrated with Integrated Composer's easy one-click updates.