The planned release date for PHP 8.0 is December 3rd.
8.0.0-RC1 is planned for September 17th.

Contao 4.9, 4.10 and 4.11 will be compatible with PHP 8.0.
Contao 4.4 will not be compatible.

ToDos (to be extended):

• Agree on ^7.2 || ^8.0 vs. >=7.2 (see sebastianbergmann/phpunit@fa50b89 for example). Result: ^7.2 || ^8.0
• Check all dependencies and add incompatible ones to this list.

Our packages:

• ausi/slug-generator add compatibility and release new version Support PHP 8.0 ausi/slug-generator#23
• toflar/psr6-symfony-http-cache-store add compatibility and release new version Version 2.4 Toflar/psr6-symfony-http-cache-store#36
• terminal42/escargot add compatibility and release new version Preparing version 1.0.0 terminal42/escargot#18
• terminal42/service-annotation-bundle add compatibility and release new version PHP 8 Compatibility terminal42/service-annotation-bundle#5
• ‌contao/image add compatibility and release new version Support PHP version 8.0 image#74
• contao/imagine-svg (is already compatible)
• contao/manager-plugin add compatibility and release new version Allow PHP 8 manager-plugin#36
• contao/maintenance-bundle-deprecated add compatibility and release new version Add compatibility with PHP 8 maintenance-bundle-deprecated#1
• contao/mobile-page-layout-bundle add compatibility and release new version Allow PHP 8 mobile-page-layout-bundle#5
• contao/tcpdf-bundle add compatibility and release new version Add compatibility with PHP 8.0 tcpdf-bundle#1
• contao/easy-coding-standard add compatibility and release new version PHP 8 Compatibility easy-coding-standard#6
• contao/phpstan add compatibility and release new version Add compatibility with PHP 8 phpstan#20
• contao/test-case add compatibility and release new version PHP 8 Compatibility test-case#9
• contao/monorepo-tools add compatibility (no release necessary) Add compatility with PHP 8.0 monorepo-tools#6
• contao/managed-edition add compatibility and release new version PHP 8 Compatibility managed-edition#56
• contao/deployer-edition add compatibility (no longer maintained)
• contao/contao and all subpackages (probably the final step) bugfixes PR: Add compatibility with PHP 8 #2535
• contao-components/installer PHP 8.0 compatibility contao-components/installer#6

Third party:

• phpunit/php-token-stream We need to update to version ^4.0 Update dependecies for PHP 8.0 compatibility #2281
• spomky-labs/otphp We need to update to ^10.0 Update dependecies for PHP 8.0 compatibility #2281
• imagine/imagine Fix compatibility with PHP 8.0 php-imagine/Imagine#740
• bacon/bacon-qr-code Add PHP 8.0 compatiblilty Bacon/BaconQrCode#74
• beberlei/assert PHP 8.0 compatibility beberlei/assert#301
• doctrine/dbal
• doctrine/doctrine-cache-bundle We need to get rid of this bundle because it is abandoned and doesn’t support PHP 8. Backport the doctrine-cache-bundle changes #2534
• doctrine/migrations Allow PHP 8 in 2.x doctrine/migrations#980
• doctrine/orm PHP8 Support doctrine/orm#8303
• doctrine/reflection PHP 8 compatibility doctrine/reflection#49
• dragonmantank/cron-expression Add compatibility with PHP 8.0 dragonmantank/cron-expression#92
• friendsofsymfony/http-cache PHP 8.0 compatibility FriendsOfSymfony/FOSHttpCache#487
• friendsofsymfony/http-cache-bundle (depends on one line above)
• knplabs/knp-menu-bundle Add php8.0 to composer.json KnpLabs/KnpMenuBundle#430
• knplabs/knp-time-bundle Add compatibility for PHP 8.0 KnpLabs/KnpTimeBundle#147
• lcobucci/jwt Require latest PHP version lcobucci/jwt#324 We need to update to version ^4.0 Upgrade scheb/2fa to version 5 (PHP 8 compatibility) #2617
• nyholm/psr7 Allow the package to be installed on PHP8 Nyholm/psr7#151
• ocramius/proxy-manager Allow PHP 8 Ocramius/ProxyManager#628 (and zendframework/zend-code and zendframework/zend-eventmanager)
• php-http/message PHP 8.0 Support php-http/message#129
• symfony-cmf/routing Allow installing on PHP 8 symfony-cmf/Routing#255
• symfony-cmf/routing-bundle PHP 8.0 compatibility symfony-cmf/routing-bundle#456
• ua-parser/uap-php PHP 8.0 compatibility ua-parser/uap-php#66