Change record status: 
Project: 
Introduced in branch: 
8.9.x
Introduced in version: 
8.9.0
Description: 

PHP 8 will be released in November 2020. Drupal 8 and Drupal 9.0 are not compatible with PHP 8.

Drupal 9.1 has been tested against PHP 8 release candidates and the core codebase will be compatible. It is possible that some of Drupal 9.1's dependencies will not be fully compatible when PHP 8 is launched. This release note will be updated with information as the situation evolves.

#3109885: [meta] Ensure compatibility of Drupal 9 with PHP 8.0 (as it evolves) contains a list of all changes made to Drupal core to make it compatible with PHP 8. Notable issues for contrib include:

Impacts: 
Site builders, administrators, editors
Module developers
Themers
Distribution developers
Updates Done (doc team, etc.)
Online documentation: 
Not done
Theming guide: 
Not done
Module developer documentation: 
Not done
Examples project: 
Not done
Coder Review: 
Not done
Coder Upgrade: 
Not done
Other: 
Other updates done